IRC 78.2014
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SUBSTRUCTURE DESIGN CODE...
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IRC:78-2014
STANDARD SPECIFICATIONS AND CODE OF PRACTICE FOR ROAD BRIDGES SECTION
:
VII
FOUNDATIONS AND SUBSTRUCTURE (Revised Edition) (Incorporating
all
Amendments and
INDIAN
Errata Published upto December, 2013)
ROADS CONGRESS 2014
Digitized by the Internet Archiive in
2014
https://archive.org/details/govlawircy201478
IRC:78-2014
STANDARD SPECIFICATIONS AND CODE OF PRACTICE FOR ROAD BRIDGES
SECTION
:
VII
FOUNDATIONS AND SUBSTRUCTURE (Revised Edition) (Incorporating
all
Amendments and Errata Published upto December,
2013)
Published by
INDIAN ROADS CONGRESS Kama Koti Marg, R.K. Puram, New Delhi- 10022 1
Price ? 700/-
(Plus packing
&
postage)
IRC:78-2014 1980 (as
First
Published
July,
First
Revision
December, 1983 (Incorporating Part 1,2
and 3
Part-I)
September, 1988
Reprinted
October, 1994
Reprinted
September, 1998
Reprinted
September, 2000
Second Revision
December, 2000 April,
:
and Amendment
to Parti)
Reprinted
Reprinted
II
2002
Reprinted
August, 2004 (Incorporates the Amendments)
Reprinted
August, 2005
Reprinted
August, 2007 (Incorporates the
Amendments
dated 30.11.2006)
Revised Edition
January, 2014 (Incorporating
:
all
Amendments and
Published upto December, 2013)
(All
Rights Reserved.
No
Part of this publication shall be reproduced,
translated or transmitted in
any form or by any means without the
permission of the Indian Roads Congress)
Printed
at:
Aravali Printers
&
Publishers Pvt.
(1000 Copies)
ii
Ltd.,
Errata
IRC:78-2014
CONTENTS Page No.
Clause No. Personnel of Bridges Specifications and Standards Committee
vii
Background
i
700
Scope
3
701
Terminology
3
i
o
701.1
Abutment
o
701.2
Afflux
o o
701.3
Balancer
A
701.4
Bearing Capacity
A
701.5
Bearing Stress
A
701.6
Cofferdam
5
701.7
Foundation
5
701.8
Pier
5
701.9
Piles
5
701.10
Retaining Wall
6
701
Substructure
7
Well Foundation
7
11
701.12
702
Notations
703
Discharge and Depth of Scour
704
705
706
7 for
Foundation Design
703.1
Design Discharge of Foundation
703.2
Mean Depth
703.3
Maximum Depth
of
Scour of
9
9 10
Scour
for
Design of Foundations
Sub-surface Exploration
11
12
704.1
Objectives
12
704.2
Zone
13
704.3
Methods
of Influence
13
of Exploration
Depth of Foundation
13
705.1
General
13
705.2
Open Foundations
14
705.3
Well Foundations
14
705.4
Pile
15
Foundations
Loads, Forces, Stability and Stresses 706.1
Loads, Forces and their Combinations
iii
15 15
IRC:78-2014
707
708
709
706.2
Horizontal Forces at Bearing Level
16
706.3
Base Pressure
17
19
Open Foundations 707.1
General
19
707.2
Design
19
707.3
Open Foundations
707.4
Construction
at
Sloped Bed
21
Profile
22 23
Well Foundations 708.1
General
23
708.2
Well Steining
23
708.3
Design Considerations
25
708.4
Stability of
708.5
Tilts
708.6
Cutting
708.7
Well Curb
28
708.8
Bottom Plug
29
708.9
Filling
708.10
Plug over
708.11
Well
708.12
Floating Caissons'
708.13
Sinking of Wells
708. 1 4
Pneumatic Sinking of Wells
30
708. 1 5
Sinking of Wells by Resorting to Blasting
31
Pile
and
26
Well Foundations
27
Shifts
28
Edge
29
the Well
29
Filling
Cap
29 30
30
'
Foundation
31
709.1
General
709.2
Requirement and Steps
709.3
Geotechnical Capacity of Pile
36
709.4
Structural Design of Piles
40
709.5
Design of
709.6
31
Pile
for
Design and
Installation
Cap
34
40
Important Consideration, Inspection/Precautions for Different
Types
41
of Piles
iv
IRC:78-2014 44
Substructure 710.1
General
44
710.2
Piers
45
710.3
Wall Piers
46
710.4
Abutments
46
710.5
Abutment Pier
47
710.6
Dirt Walls,
710.7
Retaining Walls
710.8
Pier
710.9
Cantilever
710.10
Pedestals below Bearing
Wing Walls and Return Walls
49
and Abutment Caps
Cap
48
of Abutment
49 and Pier
51
51
Appendixes Factor for Bed Material Consisting of Clay
53
1.
Guidelines for Calculating
2.
Guidelines for Sub-surface Exploration
54
3.
Procedure
67
4.
Precautions to be taken during Sinking of Wells
71
5.
Capacity of Pile Based on Pile Soil Interaction
76
6.
Filling
7.
Part-1-Pile
Silt
for Stability Calculation
Behind Abutments, Wing and Return Walls
Load Capacity by Dynamic Test Using Wave Equation
Part-2-Standard Test Method for
Low
Strain Pile Integrity Testing
V
82
84 93
IRC:78-2014
PERSONNEL OF THE BRIDGES SPECIFICATIONS AND STANDARDS COMMITTEE (As on 6.1.2014)
1.
2.
3.
Kandasamy,
Director General (RD)
C.
&
Spl. Secy, to
Govt, of India, Ministry of Road
New
(Convenor
Transport and Highways, Transport Bhavan,
Patankar, V.L.
Addl. Director General, Ministry of Road Transport and Highways
(Co-Convenor)
Transport Bhavan,
Pathak, A.P.
Chief Engineer (B) S&R, (Ministry of RoadTransport
(Member-Secretary )
Transport Bhavan,
New
New
Delhi
Delhi
&
Highways,
Delhi
Members
CPWD
4.
Agrawal, K.N.
DG(W),
5.
Alimchandani, C.R.
Chairman
Ghaziabad
(Retd.)
& Managing
Director,
STUP Consultants
(P) Ltd.,
Mumbai
MORTH, New
6.
Arora, H.C.
Chief Engineer (Retd.)
7.
Bagish, Dr. B.P.
C-2/2013, Vasant Kunj,Opp. D.P.S.New Delhi
8.
Bandyopadhyay,
Dr.
9.
Bandyopadhyay,
Dr. T.K.
10.
Banerjee, A.K.
Chief Engineer (Retd.)
MORTH, New
Delhi
11.
Banerjee,T.B.
Chief Engineer (Retd.)
MORTH, New
Delhi
12.
Basa,
13.
Bhasin,
14.
Bhowmick, Alok
Ashok P.C.
N.
New
Director, Stup Consultants (P) Ltd.
Joint Director General (Retd.)
ADG
(B), (Retd.),
Managing
MOST, New
Director, Bridge
&
Delhi
INSDAG, Kolkata
&
Director (Tech.) B. Engineers
Delhi
Builders Ltd.,
Bhubaneswar
Delhi Structural Engg. Consultants (P) Ltd.,
Noida
Mumbai
15.
Bongirwar, PL.
Advisor, L&T,
16.
Dhodapkar, A.N.
Chief Engineer (Retd.)
17.
GhoshalA
Director and Vice President,
18.
Joglekar,S.G.
Vice President,
19.
Kand,, C.V.
Chief Engineer (Retd.), MP,
20.
Koshi,
21.
Kumar, Ashok
Chief Enginee (Retd.),
22.
Kumar, Prafulla
DG
23.
Kumar, Vijay
E-in-Chief (Retd.) UP,
Ninan
DG(RD)
(RD)
MORTH, New
STUP Consultants
STUP Consultants
& Addl.Secy.,
(Retd)
(P) Ltd.
PWD MOST,
New
(Retd.)
PWD,
New
(P)
Mumbai
,
Bhopal
MORTH, New
& AS, MORT&H
vii
Delhi
Delhi
Delhi Delhi
Ltd.
Kolkata
IRC:78-2014 24.
Manjure,
25.
Mukherjee, M.K.
Chief Engineer (Retd.)
26.
Nagpal, A.K.
Prof.
27.
Narain, A.D.
DG
28.
Ninan, R:S.
Chief Engineer (Retd.)
29.
Pandey, R.K.
Chief Engineer (Planning),
30.
Parameswaran,
Concrete Co.
Director, Freyssinet Prestressed
P.Y.
IIT,
(RD)
New
MOST, New
Mumbai
Delhi
Delhi
& AS, MORT&H
New
(Retd.)
MORTH New
Delhi Delhi
MORTH, New
New
Dr.
Chief Scientist (BAS), CRRI,
S.
Vice President (Corporate Affairs).
Delhi
Delhi
Lakshmy 31.
Raizada, Pratap
32.
Rao,
33.
Roy, Dr. B.C.
Dr.
M.V.B.
Senior Consultant, Ms.
Gammon
SNC LAVALIN
India Ltd.
Mumbai
Infrastructure Pvt. Ltd.
Senior Executive Director, M/s. Consulting Engg. Services India (Pvt.) Ltd.
Gurgaon
Executive Director Construma Consultancy (P) Ltd.
34.
Saha,
35.
Sharan, G.
DG(RD) & Spl.Secy
36.
Sharma,
Chief Engineer (Retd.)
37.
Sinha, N.K.
38.
Subbarao,
Dr. G.P.
R.S.
DG(RD)&SS, Chairman
Dr.
(Retd.)
Mumbai
39.
Tandon, Mahesh
Managing
40.
Thandavan,
Chief Engineer (Retd.)
41.
Velayutham,,
V.
DG
42.
Viswanathan,
T.
7046, Sector
43.
The Executive Director
Director,
(RD) SS (Retd.) B,
Dellhi
MORTH New
Delhi
MORT&H New
Delhi
,
& Managing
Harshavardhan
K.B.
MORTH, New
(Retd.)
Director,
Construma Consultancy
Tandon Consultants
MORH, New
MORTH, New
Pocket 10
,
Mumbai
(P) Ltd.,
New
(P) Ltd
Delhi
Delhi
Delhi
Vasant Kunj ,New Delhi
RDSO, Lucknow
(B&S)
The Director and Head,
44.
(Civil
Bureau of Indian Standards,
New
Delhi
Engg.),
r;
Corresponding Members
1.
Raina, Dr. V.K.
Consultant (W.B.)
2.
Singh, R.B.
Director, Projects Consulting India (P) Ltd.
Ex-off'icio 1
.
Kandasamy, C.
2.
Prasad, Vishnu
Delhi
Members
Director General (RD) India,
New
MoRT&H
&
Special Secretary to Govt, of
and President, IRC,
New
Delhi
Secretary General, Indian Roads Congress,
Shankar viii
New
Delhi
IRC:78-2014
FOUNDATIONS AND SUBSTRUCTURE
BACKGROUND The "Standard
Specifications
and Code
Foundations and Substructure was
first
Features of Design. Later first revision Part
II
of this
the
and Amendments
1,2
and 3
Road Bridges" Section VII July 1980 as Part - General
of Practice for
published
in
was published
to Part
I
I
in
December, 1983 incorporating
as Unified Code. The second revision
code was undertaken by the Foundation and Structure Committee (B-4) and
initial
draft
was
finalized
Sarma Subsequently, .
by the Committee under the Convenorship of Shri R.H.
the draft
was reconsidered and discussed
in
various meetings
by the reconstituted Foundation, Substructure and Protective Works Committee (B-4)
under Convenorship of Shri S.A Reddi. The
as approved by Convenor
final draft
Committee was subsequently approved by the Executive Committee held on 30.8.2000.
It
was
later
approved by the Council
Kolkata on 4.11.2000 for publishing the revised IRC
in its
in
meeting
160th meeting held at
Code Section
Since then numerous amendments and errata were published to
development
in its
BSS
VII:
this
IRC: 78:2000.
Code based on
design and construction technology.
The current Revised
Edition of IRC:78 includes
all
the
amendments and
errata
published from time to time upto December, 2013.
The Revised
Edition of IRC:78 "Standard Specifications
Bridges" Section VII till
date
all
of Practice for
amendments and
Road
Errata published
was approved by Foundations and Substructure Foundation Substructure
Protective 1
- Foundation incorporating
and Code
Works and Masonry Structures Committee
6.1 0.201 3.
The Revised
Edition of IRC:78
and Standards Committee
in its
(B-3)
in
its
meeting held on
was approved by the Bridges Specifications
meeting held on 06.01 .2014 and Executive Committee
held on 09.01.2014 for publishing.
The composition
of the B-3
Committee
is
given below:
Bongirwar, P.L
Convenor
Joglekar, S.G.
Co-Convenor
Kanhere, D.K.
Member-Secretary
1
IRC:78-2014
Members Bagish, BP.
Chonkar, Ravindra
Dhiman, R.K.
Deshmukh,
Elavarson R,
Ganpule,
Dr. V.V.
Dr. V.T.
(expired on 15.03.2013)
Gandhi, Prof. S.R
Jaigopal, R.K.
Kothyari, Prof. U.C. (expired on 30.12.2012)
Karandikar, D.V.
Kand,
Dr.
C.V
Mhaiskar, Dr.S.Y.
Marwah, M.P.
Nashikkar, Jayant
Nayak,
Ray, S.
Dr. N.V.
Saha, Smt. S.DNigade,.
Subbarao,
Saha,
Singh, M.N.
Dr. G.P.
Singh, Rajeev
Velyutham,
Dr. H.
V.
Corresponding Members Basa, Ashok
Dey, Prof. S.
Heggade, V.N.
Mazumder,Prof. S.K.
Paul, Dipankar
Pitchumani, Dr. N.
Sarma, R.H.
Tarapore, Dr. Z.S.
Viswanathan,
t.
Ex-Officio
Members
C.Kandasamy
(Road Development) & Special Secretary, MoRT&H and President, IRC
Vishnu Shankar Prasad
Secretary General, IRC
Director General
2
IRC:78-2014
SCOPE
700
This code deals with the design and construction of foundations and substructure
road bridges. The provisions of
code are meant to serve as a guide to both the design and construction engineers, but mere compliance with the provisions stipulated herein will not relieve them in any way of their responsibility for the stability and soundness of the structure designed and erected. for
701 The
this
TERMINOLOGY
following definitions shall be applicable for the purpose of this code.
Abutment
701.1
The end support
of the
approaches behind
Box
701.1.1
When
fully
deck (superstructure) of a bridge, which also retains
earth,
fill
of
or partly.
type abutment
and return
wall
the return walls on two sides are integrated with abutment and a back wall parallel to
abutment
is
provided at the end of returns with or without additional internal wall along or
across length,
701.1.2
this structure is called
box type abutment and return
end
wall, or
block.
Non-load bearing abutment
Abutment, which supports the end span of less than 5 m. 701.1.3
Non-spill through
An abutment 701.1.4
structure
Spill
abutment
where the
soil is
not allowed to
spill
through.
through abutment
An abutment where
soil is
allowed to
spill
through gaps, along the length of abutment, such
column structure where columns are placed below deck beams and gap
as,
free to
spill
earth. (Spilling of earth should not
be permitted above a
level of
in
500
between
is
mm below
the bottom of bearings).
701.2
The
Afflux
rise in the flood level of the river
immediately on the upstream of a bridge as a result of
obstruction to natural flow caused by the construction of the bridge and
3
its
approaches.
IRC:78-2014 Balancer
701.3
A bridge/culvert like structure of the
embankment
provided on
to other side, for
embankment to
allow flow of water from one side
purpose of avoiding heading up of water on one side
or for avoiding blocking the entry to the other side.
Bearing Capacity
701.4
The supporting power
expressed as bearing stress
of soil/rock
is
referred to as
it
bearing
capacity.
Allowable bearing pressure
701.4.1
It
the
is
maximum
gross pressure intensity at which neither the
accounting for appropriate factor of safety) nor there permissible
is
which
is
expected
to
be detrimental
shear, (after
excessive settlement beyond
to the structure.
Net safe bearing capacity
701 .4.2
it
limits,
is
soil fails in
the net ultimate bearing capacity divided by a factor of safety as per Clause
706.3.1.1.1.
701 .4.3
It
is
Net ultimate bearing capacity
minimum
the
701 .4.4
net pressure intensity causing shear failure of the
Safe bearing capacity
The maximum pressure, which the is
is
the
fails in
can carry safely without
risk of
shear
failure
and
it
Ultimate gross bearing capacity
minimum gross pressure
Bearing Stress
701 .5. 1
Gross pressure
is
intensity at the
base of the foundation
which the
soil
intensity
the total pressure at the base of the foundation on
of load
at
shear.
701.5
It
soil
equal to the net safe bearing capacity plus original overburden pressure.
701 .4.5
It
soil.
and the weight
701.5.2
of the earth
Net pressure
fill.
intensity
4
soil
due
to the possible
combinations
IRC:78-2014 It
is
the difference
intensities of the
gross pressure and the original overburden pressure.
Cofferdam
701.6
A
in
structure temporary built for the purpose of excluding water or soil sufficiently to permit
construction or proceed without excessive
pumping and
to
support the surrounding
ground.
Foundation
701.7
The
part of a bridge
701.8
in
direct contact with
and transmitting load
to the
founding strata.
Pier
Intermediate supports of the deck (superstructure) of a bridge.
Abutment pier
701 .8.1
Generally use
even
if
in
multiple
span arch bridges. Abutment
one side arch span collapses
it
would be
pier
is
designed
for
These are provided
safe.
a condition that
after three or five
spans.
701.9
Piles
701.9.1
Bearing/friction piles
A
pile
driven or cast-in-situ for transmitting the weight of a structure to the founding strata
by the resistance developed at the
pile
base and by
the load mainly by the resistance developed at pile,
and
701 .9.2
if
mainly by
Bored
A pile formed with it
along
its
base,
it
surface, as a friction
is
along
its
If it
supports
referred to as an end-bearing
pile.
cast-in-situ pile
or without a casing by boring a hole
in
the ground and subsequently
filling
pile
Driven cast-in-situ pile
formed
in
the ground by driving a permanent or temporary casing, and
plain or reinforced concrete.
701.9.4
A
surface.
with plain or reinforced concrete.
701 .9.3
A
friction
its
friction
pile
Driven pile
driven into the ground by the blows of a
5
hammer by
a vibrator.
filling
if
with
IRC:78-2014 701.9.5
A
Precast pile
reinforced or prestressed concrete pile cast before driving, or installing
in
bore and
grouted.
701.9.6
A pile
installed at
701.9.7
One
Raker or batter pile an
inclination to the vertical.
Sheet pile
or a row of piles driven or formed
continuous
wall,
in
the ground adjacent to one another
each generally provided with a connecting
to resist mainly lateral forces
and
to
reduce seepage;
it
joint or interlock,
may be
in
a
designed
vertical or at
an
inclination.
701 .9.8
A
pile
Tension pile
subjected to tension/uplift
701.9.9
a load
is
applied to determine and/or confirm the load characteristics (ultimate
load/working load) of the
One
pile
and the surrounding ground.
Working pile
of the piles forming the foundation of the structure.
701.10
A wall
Retaining Wall
designed
701.10.1
A
called tension pile.
Test pile
A pile to which
701 .9.1 0
is
to resist the
pressure of earth
filling
behind.
Return wall
wall adjacent to
abutment generally
parallel to
road or flared up to increased width and
raised upto the top of road.
701.10.2
A wall
Toe wall
built at
the end of the slope of earthen
or pitching on
embankment to prevent
embankment.
6
slipping of earth and/
IRC:78-2014
Wing
701.10.3
A wall
wall
adjacent to abutment with
upto ground level or a
little
its
above
of road or parallel to the river
top upto road top level near abutment and sloping
at the other end. This is generally at
and follows
The bridge
structure,
superstructure.
earthen banks.
A type
such as, pier and abutment above the foundation and supporting the
shall include returns
It
of foundation
where a
part of the structure
and sunk through ground or water dredge
and wing walls but exclude bearings.
Well Foundation
701.12
hollow, which
is
to the prescribed
is
generally
built in
parts
depth by removing earth through
hole.
710.12.1
Tilt
of a well
inclination of the axis of the well
between the axis
701.12.2
The
45° to the alignment
Substructure
;{ t
The
profile or
down
of the well
and the
from the
vertical
expressed as the tangent of the angle
vertical.
Shift of a well
horizontal displacement of the centre of the well at
its
base
in its final
position from
its
designed position.
702 NOTATIONS For the purpose of
A
this
code, the following notations have been adopted:
Dispersed concentric area 1
A2
Loaded area
B
Width between outer faces of
group
pile
in
plan
parallel
to the
direction
of
movement
C
The allowable bearing pressure
c
Cohesion
Co
The permissible
direct
with near uniform distribution on the founding strata
compressive stress
base
D
Diameter of
pile
7
in
concrete at the bearing area of the
IRC:78-2014
Db
Discharge
d
External diameter of circular well
dm
Weighted mean diameter
dsm
Mean depth ~
Fb
Longitudinal force
F
Centrifugal force
in
cubic metre/sec, (cumecs) per metre width
scour
of
in
due
in
in
metre
mm of bed
metre below flood
materiaj level
to braking
...
,
,
cf
Fw
Deformation effects
Fh
Horizontal force
Fep
pressure Earth r
Feq
Seismic force
Fer
Erection effects
F
Frictional force at bearings f
Fjm
Impact due to floating bodies
Fs
Secondary
F
Water Current
F
Temperature effects [See Note
effects
(i)]
te
Fwp
Wave
pressure [See Note
G
Dead
load
Gb
Buoyancy
Gs
Snow
h
Minimum thickness
Kg
Co-efficient of active earth pressure
Kp
Co-efficient of passive earth pressure
K
.
sf
L
Silt
(ii)]
load of steining
in
metre
factor
Length between outer faces of
pile
group
in
plan parallel to the direction of
movement l te
Movement
of
deck over bearings, other than due
to applied force
Depth of well
/
/
s
Depth of well
in
metre, up to
MSL.
N
Standard penetration test value
Pa
Total active pressure
Pp
Total passive pressure
Q
Live load
:
8
IRC:78-2014
Rg
Dead
Rq
Live load reaction
V
Shear
w
Wind load
CL
Reduction factor
R H
Ratio of lona side to the short side of the footina
su
Undrained shear strenath
a
Undrained III W chohesion \/ w
Li
Co-efficient of friction
0
Angle of
8
Settlement of
pile
S
Settlement of
pile
load reaction
r
g
1
NOTES:
1
'w?
1
rating of elastomeric bearing
(»4
*wfl
\_.
1
1
1
I
1
V—/
1
1
internal friction
group
Temperature effects (FJ in this context is not the frictional force due of bearing but that which is caused by rib shortening, etc.
i)
The wave forces
ii)
to the
movement
be determined by suitable analysis considering drawing and on single structural members based on rational methods or case of group of piles, piers, etc., proximity effects shall also be
shall
inertia forces, etc.,
model
studies. In
considered.
703
*
DISCHARGE AND DEPTH OF SCOUR FOR FOUNDATION DESIGN
703.1
Design Discharge of Foundation
703.1.1
To provide
be designed
for
for
and adequate margin
of safety, the scour for foundation shall
a larger discharge over the design discharge determined as per IRC:5 as
given below:
Catchment area
in
km
Increase over design
Discharge 0,-3000
NOTES:
i)
For
-
percent
30
3000- 10000 10000-40000
Above
in
30-20 20-10
;
400Q0
intermediate
10 values
of
catchment
adopted.
9
area,
linear
interpolation
may be
IRC:78-2014 The minimum
ii)
vertical
clearance above the
need not be increased due
Mean Depth
703.2
to larger
HFL
already determined as per IRC:5
discharge calculated above.
of Scour
The mean scour depth below Highest Flood Level (HFL)
for natural
channels flowing over
scourable bed can be calculated theoretically from the following equation:
1 dsm = 1.34/-^) 3
\KsJ
Where
Db
=
The design discharge
for foundation
per metre width of effective
waterway.
K
=
Silt
sf
factor for a representative
sample
of
bed material obtained upto
the level of anticipated deepest scour.
The value
703.2.1
of
Db may
be determined by dividing the design discharge
foundation by lower of theoretical and actual effective linear waterway as given
703.2.2
'K
'
is
sf
in
given by the expression
1
in
for
IRC:5.
J6jd^ d m being the weighted mean diameter
millimetre.
703.2.2.1
The value
of
K
sf
for various
grades of sandy bed are given below forready
reference and adoption:
dm
Type of bed material Coarse silt sand Medium sand Coarse sand Fine bajri and sand Heavy sand
Silt/fine
703.2.2.2
No
scour depth
703.2.3
bend
is
0.081 to 0.158
0.5 to 0.7
0.223 to 0.505
0.85 to 1.25
0.725
1.5
0.988
1.75
1.29 to 2.00
2.0 to 2.42
there
of the stream
variation of type of
scour depth for bed material
and boulders (normally having weighted diameter more than 2.00
available. In
may be
If
0.35
rational formula or data for determining
consisting of gravels
and clayey bed
sf
0.04
absence
of
any data on scour
calculated following the guidelines given
is
in
any predominant concentration
of flow
immediate upstream or downstream or
bed materia! across the width 10
for
such material, the mean
in
Appendix-1.
in
any
for
part of
waterway due
any other reason,
of channel, then
mm)
like,
to
wide
mean scour depth may be
IRC:78-2014 calculated by dividing the waterway into compartments as per the concentration of flow.
703.2.4
In
case of bridge mainly adopted as balancer, the mean scour depth
be taken as (Highest Flood Level-Lowest Bed Level) divided by
'd sm
'
may
1.27.
Scour depth may be determined by actual observations wherever possible. This is particularly required for clayey and bouldery strata. Soundings, wherever possible, shall be taken in the vicinity of the site for the proposed bridge and for any structures nearby. Such soundings are best during or immediately after a flood before the scour holes have had time to be silted up. The mean scour depth may be fixed based on such observations and theoretical calculation. 703.2.5
Maximum Depth
703.3
of
Scour for Design of Foundation
The maximum depth of scour below the Highest Flood Level (HFL) for the design and abutments having individual foundations without any floor protection may be
703.3.1 of piers
considered as follows.
703 .3.7.7
Flood without seismic combination i)
For piers
-
2.0
dsm
ii)
For abutments
-
a)
.27
1
bed b) 2.00 '
703 3 .
7
.
.
2
dsm
with approach retained or lowest
level
dsm
whichever
with scour
is
all
deeper.
around.
Flood with seismic combination
For considering load combination of flood and seismic loads (together with other appropriate
combinations given elsewhere) the
be reduced by multiplying 703.3.1.3
maximum
maximum depth
of scour given
in
Clause 703.3.1 .1 may
factor of 0.9.
For low water level (withoutflood conditions) combined with seismiccombination level of
scour below high flood
level
can be assumed as 0.8 times scour given
in
Clause 703.3.1.
NOTE
:
In
respect of viaduct/ROB having no possibility of scour, resistance of
soil
considered below depth of excavation for services construction, or 2.0
ground 703.3.2
level
whichever
is
maximum
scour depth
i)
In
a straight reach
ii)
In
a bend
m
below
greater.
For the design of floor protection works for
following values of
may be
may be 1
.27
1.50 11
raft
or
open foundations, the
adopted:
dsm
dsm
or on the basis of concentration of flow
IRC:78-2014
The
length of apron on upstream
may be
0.7 times of the
same on downstream.
Special studies should be undertaken for determining the
703.4
depth for the design of foundations
in all
situations
where abnormal
maximum
scour
conditions, such as,
the following are encountered:
a bridge being located on a bend of the river involving a curvilinear flow, or
i)
excessive shoal formation, or a bridge being located at a site where the deep channel
ii)
one
in
the river hugs to
side, or
iii)
a bridge having very thick piers inducing heavy local scours, or
iv)
where the
v)
where a bridge river
obliquity of flow in the river
is
considerable, or
is
required to be constructed across a canal, or across a
downstream
of storage works, with the possibility of the relatively
clear water inducing greater scours, or
a bridge
vi)
in
the vicinity of a
where concentration likely to affect
An
vii)
weir,
barrage or other
irrigation structures
of flow, aggradations/degradation of bed, etc. are
the behavior of the structures.
when
additional tow-lane bridge
major
NOTE:
dam,
located near to the existing bridge, on
rivers.
These studies
shall
be conducted
for the increase
discharge calculated vide Clause
703.1.1.
703.5
If
a river
is
of a flashy nature
and bed does not lend
itself
readily to the
dsm and maximum depth of scour as maximum depth shall be assessed from
scouring effect of floods, the theoretical formula for
recommended
shall not apply. In
such cases, the
actual observations.
704
SUB-SURFACE EXPLORATION
Objectives
704.1
The i)
objectives of the sub-surface exploration are:
During Preliminary Investigation Stage
As a
part of site selection process to study existing geological
information,
known data and banks,
maps and
other
previously prepared and available site investigation reports, of
nearby structures,
etc.,
which
will
help
in
if
any, surface examination about river
narrowing
12
down
bed
of sites under consideration
IRC:78-2014 for further studies for project preparation stage.
Detailed Investigation Stage
ii)
To determine the characteristics of the existing geo-materials,
bed material
in
bridge sites
such a way as
in
water courses,
etc. in
like, soil,
rock,
the zone of influence of the proposed
to establish the
design parameters which influence
the choice and design details of the various structural elements, especially the
foundation type.
During Construction Stage
iii)
To confirm the characteristics of geo-materials established
in
on which the design choices are made and
same
suit
Zone
(ii)
based
or modify to
the conditions met at specific foundation locations.
Zone
704.2
to re-confirm the
stage
of influence
of Influence
mentioned
Clause 704.1
in
(ii)
is
defined as the
full
length of the bridge
and part of approaches covering, (but not restricted to), the full flood zone for water courses, and upto depth below proposed foundation levels where influence of stresses due to foundation is likely to affect the behaviour of the structure, including settlement, subsidence under ground flow of water, etc. The width of the land strip on either side of the proposed structure should include zones in which the hydraulic characteristics of river water are likely to be changed affecting flow patterns, scour, etc. including portion of wing/return wall
Methods of Exploration
704.3
A
large variety of investigative
methods are
available.
A most
suitable
and appropriate
combination of these shall be chosen. Guidelines for choice of types of investigations,
need be established, the
properties of geo-materials that
laboratory testing are given
in
in-situ
testing,
sampling,
Appendix-2. This may be further supplemented by
specialized techniques depending on the need.
705 :
General
705.1
The foundation evaluated
DEPTH OF FOUNDATION
in
shall
be designed
to
withstand the worst combination of loads and forces
accordance with the provisions of Clause 706. The foundations
taken to such depth that they are safe against scour or protected from
it.
shall
Apart from
be
this,
the depth should also be sufficient from consideration of bearing capacity, settlement, liquefaction potential, stability
depth below
It.
In
case
and
of bridges
suitability of strata at the
founding level and sufficient
where the mean scour depth 'dsm' 13
is
calculated with
IRC:78-2014 Clause 703.2, the depth of foundation in
the
shall not
be less than those of existing structures
vicinity.
705.2
Open Foundation
705.2.1
In soil
The embedment
of foundations
shail
in soil
be based on correct assessment of anticipated
scour considering the values given under Clause 703.
may be
Foundation
taken
down
provided good bearing stratum
to a
is
comparatively shallow depth below the bed surface
available,
The minimum depth
of
open foundations
but not less than 2.0
m
below the scour
705.2.2
In
and the foundation
shall
be upto stratum having safe bearing capacity
is
bed
level or the protected
level.
rocks
For open foundations resting on rock, the depth of rock, which expert
protected against scour.
is
weathered or fissured,
the rock existing below.
shail
be excluded
Where foundations
in
in
the opinion of the geological
deciding the depth of
embedment
into
are to rest on credible rocks, caution shall be
exercised to establish the foundation level at sufficient depth, so as to ensure that they
do not get undermined, keeping for conditions stipulated
below
shall
in
view the continued erosion of the bed. After allowing
above the minimum embedment
be as follows, which
in
case of sloping rock
of the foundations into the rock
profile
can be provided by properly
benching the foundations.
Embedment depth
Type of Rock a)
For rocks of moderately strong and above classification of rock (under clause 8.2 of
UCS
of
more than 12.5
core to get the
UCS
MPA or where
it
but extrapolated
is
in
table 2 of
0.6
m
1.5
m
appendix 2) having not possible to take
SPT N
value
is
more
than 500 b)
For rock of moderately
weak and below
in
table 2 of classifi-
cation of rock (under clause 8.2 of appendix 2) having
UCS
<
1
2.5
MPA but
> 2.5
to take core to get the
more than 100 but
MPA or where
UCS
less than
705.3
Wei! Foundations
705.3.1
In soil
it
is
but extrapolated
500
14
not possible
SPT N
value
is
IRC:78-2014 Well foundations shall be taken
maximum depth 705.3.2
As
In
of scour
to
a depth which
below the design scour
will
provide a
level specified in
minimum
zone,
all
shall
be taken by
the
all
around the periphery on sound rock
likely
methods
to
in
each case
mentioned above
make
a
(i.e.,
sump
(shear key) of 300
Diameter of sump
minimum
.5m
1
rock and projected 1.5
mm
in
m
embedment. The extent
may be
above. These
mm
hard rock or 600
Six dowel bars of 25
.
shall
ensure overall and long-term safety of the structure.
to
chiseling/blasting.
size of
and
be decided by the Engineer-in-charge keeping
shall
1
.5 to
2
pneumatic
of sinking including
be evenly
devoid of fissures, cavities, weathered
extent of erosion, etc.) by providing adequate
and embedment factors
the
Clause 703.3.
sinking (where considered necessary), dewatering, etc. to foundation level
seated
rd
grip of 1/3
rocks
as possible, the wells
far
down
m
in
It
of seating
in
is
view the
advisable
soft rock inside the well
by
less than inner dredge-hole subject to a
mm dia deformed
may be anchored
in
may be anchored
bars
minimum 65
1
.5
m
in
mm dia boreholes and
grouted with 1:172 cement mortar.
Foundations
705.4
Pile
705.4.1
In soil,
minimum 705.4.2
the
minimum depth
length required for developing
In
of foundations full fixity
below the point of
as calculated by any
rocks, the pile should be taken
down
fixity
should be the
rational formula.
to rock strata
devoid of any
likely
extension of erosion and properly socketed as required by the design.
706 LOADS, FORCES, STABILITY 706.1
AND STRESSES
Loads, Forces and their Combinations
The loads and forces may be evaluated as per IRC:6 and the purpose of this code will be as follows:
706.1.1 for
Combination
Combination
G + (Qor GJ + Fwc + F + F
I):
f
II): i)
+
b
+
G+ F
cf
+
F, ep
W+ F
wp
or wp
or ii)
Combination
iii)
+F +Fwp :
G
+ Fwc + Gb + Fep +
15
Fer
+ Ff +
their
(WorFe q)
combinations
IRC.78-2014
The permissible increase
706.1.2
stresses
in
the various
in
members
be 33V 3
will
percent for the combination of wind (W) and 50 percent for the combination with seismic (Fe for
J
The permissible increase
or (FJ.
all
allowable base pressure should be 25 percent
in
combinations except combination
secondary effects (FJ deformation effects
i)
(f
d)
then permissible increase
combination with
i)
bearing pressure
will
However, when temperature effects (FJ, are also to be considered for any members in in
stresses
Horizontal Forces at Bearing Level
706.2.1
Simply supported spans
706.2.1.1
For
supported
simply
type)
various
members and
on
span with
supports,
stiff
longitudinal direction shall
fixed
be as given below
and
forces
horizontal
Fixed Bearing
at
free
the
bearings bearing
(other level
:
Free Bearing
Non-Seismic Combinations Greater of the two values given below
:
F h -fj(R+RJ
i)
Seismic Combinations F,
where
Fh
- Applied horizontal force
R R
- Reaction at the free end due to dead load - Reaction at the free end due to
live
load
q
p
allowable
be 15 percent.
706.2
Elastomeric
in
- Co-efficient of
assumed
to
friction at
have the allowable values:
)
For steel
i)
For concrete
ii)
For sliding bearings: a)
the movable bearing which shall be
roller
bearings
roller
bearings
Steel on cast iron or steel on steel
16
0.03 0.05
0.4
in
than the
!RC:78-2014 Grey cast
b)
on grey cast
iron
iron
0.3
:
(Mechanites) c)
Concrete over concrete
d)
Telflon
on stainless
0.5
:
steel
0.03 and 0.05
:
(whichever 706.2.1.2
In
case of simply supported small spans upto 10
provided, horizontal force
-Jj~
706.2. 1.3
in
orjj(Rg) whichever
resting
=
Shear
=
Movement
r
/ te
706.2.2
and where no bearings are
is
greater sitting
on
identical eiectrometric bearings at
on unyielding supports. +
Force of each end =
V
governing)
the longitudinal direction at the bearing level shall be
For a simply supported span
each end and
m
is
K4
rating of the eiectrometric bearings
of
deck above bearing, other than due
Simply supported and continuous span on
flexible
to applied forces
supports
The distribution of applied longitudinal horizontal force (e.g., braking, seismic, wind, etc.) depends solely on shear rating of the supports and may be estimated in proportion to the ratio of individual shear rating of a support to the sum of the shear ratings of all the supports. Shear rating of a support is the horizontal force required to move the top of the 706.2.2.1
support through a unit distance taking into account horizontal deformation of the bridge, flexing of the support
and
rotation of the foundation.
706.3
Base Pressure
706.3.1
The allowable bearing pressure and the settlement
different loads
and
testing.
and stresses may be determined on the basis
Though the help
of relevant Indian Standard
taken, the allowable bearing pressure
may be
pressure at the base without deducting the
soil
For open foundations and well foundation resting on taken as 2.5 for
17
may be
displaced can be computed.
706.3.
may be
of Practice
calculated as gross so that the gross
Factor of safety
pressure on ultimate bearing capacity
under
of sub-soil exploration
Code
706. 3.1.1
1. 1. 1
characteristics
soil,
soil.
the allowable bearing
IRC:78-2014 706.3.
1.
1.2
For open foundations and well foundation resting on rock, the allowable bearing
pressure on rock
may be decided upon
not only on the strength of parent rock but also on
overall characteristics particularly deficiencies, like, joints,
zones,
absence
etc. In
to
shall
in
is
to
be further
restricted to not
Clause 706.1.1. For Factor of safety
of the parent rock
may be
taken
in
over 3
case of
pile
MPa
for load
combination
(i)
foundation the clause 709.3.2
be referred
The intermediate geo-materia! as
weathered
8 unless otherwise indicated on the basis of local experience. The allowable bearing
pressure, thus, obtained
given
faults,
such details or analysis of overall characteristics, the value of
based on unconfined compressive strength
factor of safety
as 6
of
bedding planes,
like
disintegrated weathered or very soft rock
may be treated
soil.
706.3.2
Allowable settlement/differential settlement
706.3.2.1
The calculated
settlement between the foundations of simply
differential
supported spans shall not exceed
1
in
400
of the distance
between the two foundations from
the consideration of tolerable riding quality unless provision has
been made
for rectification
of this settlement.
706.3.2.2 to
be fixed
for
to differential settlement, the tolerable limit
has
each case separately.
Permissible tension at the base of foundation
706.3.3
706.3.3.
case of structures sensitive
In
1
706.3.3.2
No
In
tension shall be permitted under any combination of loads on
case of rock
if
tension
is
found
the base area should be reduced to a size
to
be developed
where no tension
at the
will
soils.
base of foundation,
occur and base pressure
The maximum pressure on such reduced area should not exceed allowable bearing pressure. Such reduced area shall not be less than 67 percent of the total area is
recalculated.
for load
combination including seismic, or impact of barge, and 80 percent for other load
combinations.
706. 3. 4
Factor of safety for stability
Factors of safety against overturning and sliding are given below. These are mainly relevant
18
IRC:78-2014 for
open foundations:
values
With Seismic
Seismic Case
Case
i)
Against overturning
2
1.5
ii)
Against sliding
1.5
1.25
iii)
Against deep-seated failure
1.25
1.15
Frictional co-efficient
Founding
Without
soil
in
may be
between concrete and
soil/rock will
be Tan 0,
0
being angle of
friction.
foundation of bridge being generally properly consolidated, following
adopted:
and concrete
Friction co-efficient
between
Friction co-efficient
between rock and concrete
soil
0.5 0.8 for
good rock and 0.7
for fissured rock
706.3.5
Pile foundations
The allowable
load, the allowable settlement/differential settlement
determine the
same
for pile
foundations are given
707
in
and the procedures
to
Clause 709.
OPEN FOUNDATIONS
707.1
Genera!
707.1.1
Provision of the Clause under 707 shall apply for design of isolated footings
and, where applicable, to combined footings, and
707.1.2
Open foundations may be
stratum which
is
inerodible or
provided where the foundations can be
where the extent
foundations are to be reliably protected by walls or/and launching aprons as
rafts.
may be
of scour of the
means
bed
is
reliably
laid in
a
known. The
of suitably designed aprons, cut-off
necessary.
707.2
Design
707.2.1
The thickness
707.2.2
Bending moments
707.2.2.1
For solid wall type substructure with one-way reinforced footing, the bending
of the footings shall not
moments can be determined as one-way
be less than 300 mm.
slab for the unit width subjected to worst
combination of loads and forces.
For two-way
footing,
bending moment at any section of the footing
shall
determined by passing a
vertical
plane through the footing and computing the
moment
707.2.2.2
of the forces acting over the entire
area of footings one side of the
19
vertical plane.
be
The
IRC:78-2014 section of bending shall be at the face of the solid column.
critical
707.2.2.3
In
circular footings or polygonal footings, the
case of
bending moments
may be determined in accordance with any rational method. Methods Timoshenko and Rowe for Plate Analysis are acceptable.
the footing
For combined footings supporting two or more columns, the
707.2.2.4
bending moments along the axis of the columns shall be Further, for determination of critical sections for walls,
any
method
The shear
707.2.3 is
rational
of analysis
'd' is
'd'
given by
sections for
at the face of the columns/walls.
bending moments between the column/
be adopted.
strength of the footing
the vertical section at a distance
critical
in
may be checked
at the critical section
which
from the face of the wall for one-way action where
the effective depth of the section at the face of the wall.
For two-way action for slab or footing, the
707.2.3.1
perpendicular to plan of slab and so located that
approach closer than
half the effective
perimeter
its
section
critical is
should be
minimum, but need not
depth from the perimeter of concentrated load or
reaction area.
To ensure proper load
707.2.4
width of footing equal to 1:3
is
transfer, a limiting value of ratio of
specified.
effective at the critical section shall
this, for
be the minimum depth
between the extreme edge of the footing all
Based on
at the
depth to length/
sloped footings the depth
end plus
to the critical section for
1/3
rd
of the distance
design of the footing for
purposes.
The
707.2.5
critical
section for checking development length of reinforcement bars
should be taken to be the vertical
section as given
planes where abrupt changes
707.2.6
Tensile
reii
in
in
Clause 707.2.3 and also
all
other
section occur.
iforcei lent i
The tensile reinforcement shall provide a moment of resistance at least equal bending moment on the section calculated in accordance with Clause 707.2.2.
707.2.6. to the
same
1
707.2.6.2
The
resisiting section
a)
tensile reinforcement shall
as below:
In
one-way reinforced
calculated for b)
be distributed across the corresponding
in
footing,
critical unit
reinforcement shall be
width as mentioned
two-way reinforced square
direction shall
the
in
Clause 707.2.2.1.
footing, the reinforcement extending in
be distributed uniformly across the
20
same as
full
each
section of the footing.
!RC:78-2014 c)
two-way reinforced rectangular
in
footing, the reinforcement in the long
be distributed uniformly across the
direction shall
For reinforcement
full
width of the footing.
the short direction, a central band equal to the short
in
marked along the length
side of the footing shall be
portion of the reinforcement determined
of the footing
and
accordance with the equation
in
given below shall be uniformly distributed across the central band:
Reinforcement Total
Reinforcement
Where
/3
= the
in
ratio of
The remainder
band
centra!
in
2 '
short direction
the long side to the short side of the footing
of the reinforcement shall be uniformly distributed
in
the
outer portions of the footing. d)
In
the case of a circular shaped footing, the reinforcement shall be provided
on the basis of the
moments
in
critical
values of radial and circumferential bending
the form of radial and circumferential steel. Alternatively,
equivalent orthogonal grid can be provided.
The area
707.2.7
of tension reinforcement should as per IRC: 112,
Clause number
16.5.1.1
707.2.8
metre
in
faces of the footing shall be provided with a minimum steel of 250
All
each
direction for
more than 300 mm. This that face,
if
707.2.9 pier or
all
grades of reinforcement. Spacing of these bars
steel
may be
mm
shall not
2 /
be
considered to be acting as tensile reinforcement on
required from the design considerations.
In
column
case of shall
piain concrete, brick or stone
masonry
be taken as dispersed through the footing
at
footings, the load from the
an angle not exceeding 45°
to vertical.
707.3
Open Foundations
707.3.1
Open
slope
is
foundations
at
may
Sloped Bed rest
Profile
on sloped bed
profile
provided the
stability of
the
ensured. The footings shall be located on a horizontal base.
707.3.2
For the foundations adjacent to each other, the pressure coming from the
foundations
laid
on the higher
level
should be duly considered on the foundations at the
lower level due to the dispersions of the pressure from the foundation at the higher
The distance between the two foundations to
minimize
this effect taking into
at different levels
account the nature of 21
soil.
may be decided
in
level.
such a way
IRC:78-2014 707.4
Construction
707.4. 1
The
protective
works
shall
be completed before the floods so that the foundation
does not get undermined.
Excavation on open foundations shall be done after taking necessary safety
707.4.2
precautions for which guidance
Where
707.4.3 to
blasting
is
may be
taken from IS 3764.
required to be
endanger adjoining foundations or other
controlled blasting, providing suitable
done
structures,
mat cover
excavation
for
in
and
rock,
is
likely
necessary precautions, such as,
to prevent flying of debris, etc. shall
be
taken to prevent any damage.
Condition for laying of foundations
7 07 .4 .4
707.4.4.
1
of dewatering by levelling
pumping or depression
course of 100
707.4.4.2 the situation
method
Normally, the open foundations should be laid dry and every available
If
it
is
of water by well point, etc.
mm thickness in M
may be
resorted
such that the percolation
foundation concrete
may be
laid
A
10 (1:3:6) shall be provided below foundation.
determined before-hand that the foundations connot be
is
to.
is
laid
dry or
too heavy for keeping the foundation dry, the
under water only by tremie pipe.
In
case of flowing water
or artesian springs, the flow shall be stopped or reduced as far as possible at the time of placing of concrete.
No pumping
of
water shall be permitted from the time of placing of
concrete upto 24 hours after placement.
707.4.5 All spaces excavated and not occupied by abutments, pier or other permanent works shall be refilled with earth upto the surface of the surrounding ground, with sufficient allowance for settlement. All backfill shall be thoroughly compacted and in general, its top surface shall be neatly graded.
707.4.6
In
case of excavation
with concrete of
707.4.6.1
If
M
the depth of
above may be
707.4.6.2
around the footing
rock, the trenches
be
shall
filled-up
15 grade upto top of the rock.
above the foundation portion
in
level, filled
fill
required
is
then concrete
more than
1.5
may be filled
m
in
soft rock or 0.6
upto this level by
M
m
in
hard rock
15 concrete and
by concrete or by boulders grouted with cement.
For design of foundation on rock
in river
22
bridges, the design loads
and forces
IRC:78-2014 shall
be considered upto the bottom of
footing.
The
load of
need not be considered
filling
in
stability calculations
708
WELL FOUNDATIONS
General
708.1
deep water cannels shall comprise of properly dimensioned caissons preferably having a single dredge hole. While selecting the shape, size and type of well, the size of abutment and pier to be accommodated, need for effecting streamline flow, the possibility of the use of pneumatic sinking, the anticipated depth of foundation and the nature of data to be penetrated should be kept in view. The minimum dimensions of dredge-hole shall not be less than 3 m. In case there is deep standing water, properly designed floating caissons may be used as per Clause 708.12. Foundations supporting the superstructure located
708.1.1
However,
in
tidal rivers,
the
number
708.1.2 in-charge
case of larger bridges across
rivers in
channels with inland waterway
traffic
of intermediate foundations shall be
If
in
wide flood plains prone
and bridges reduced as
coastal/marine locations,
in
far
as practicable.
the external diameter of single circular well exceeds 12
may
to scour, delta/
m
then Engineer-
take recourse to any of the following: Stress
a)
in
steining shall be evaluated using 3-Dimensional Finite
Method (3D FEM) or any other Stiffening by
b)
suitable analytical method.
compartments may be done
Design of such stiffened wells
Element
for the single circular well.
shall call for
supplemental design and
construction specifications,
Twin D-shaped well
c)
The considered when 708.1.3
may be adopted
conditions arising out of sand blow, circular well
is
if
anticipated,
should be duly
analysed using 3D FEM/suitable analytical method or
stiffened circular wells are used.
708.1.4
Bottom plug of well should be suitably designed
force acting on
it
to resist
maximum upward
during construction following plugging as well as during
life
span of the
structure.
708.2
Well Steining
708.2.1
Thickness of the steining should be such so that
well without excessive kentledge
and without
23
getting
damaged
it
is
possible to sink the
during sinking or during
IRC:78-2014 excessive
rectifying the
tilts
and
shifts.
The
steining should also
be able
earth pressure developed during sand blow or other conditions,
like,
to resist differential
sudden drop.
Stresses at various levels of the steining should be within permissible conditions for loads that
Use
may be
all
transferred to the well.
of cellular steining with
well steining shall not
under
limits
two or more shells or use of composite material 12
for wells upto
be permitted
m
in
diameter.
Steining thickness 708.2.3.1
The minimum thickness
of the well steining shall not
mm
be less than 500
and
satisfy the following relationship:
h
KdVT
=
minimum thickness
m
h
=
d
= external diameter of circular well of twin
D wells
(for floating
bed
in
smaller dimension
= depth of wells
/
of steining
in
in
dumb
plan
in
bell
shaped
'
in
case of
metres
LWL whichever
metre below top of well cap or
caisson 7
well or
may- be taken as depth
of well
in
is
more
metres below
level).
K - a constant Value of
708.2.3.2
K shall
follows:
K = 0.03 K = 0.05 K = 0.039
cement concrete brick masonry
i)
Well
in
ii)
Well
in
iii)
Twin
D wells
The minimum
be as
steining thickness
may be
varied from
above
in
following
conditions:
Strata
a)
Very
b)
Hard clay
c)
Boulder strata or well resting on
soft clay strata
strata
Variation from
f
be
Recommended
minimum
variation upto
Reduced
10%
Increased
10%
Increased
10%
rock involving blasting
24
SRC:78-2014 However, following aspects may also be considered depending on the
708.2.3.3
Very soft clay strata: Main
a)
criteria for
to prevent the well penetrating
so reduced, the steining
shall
by
its
reduction
own
in
weight.
strata:
steining thickness
When
be adequately reinforced,
the thickness
is is
to get sufficient
strength.
Hard clay
b)
in
Depending on the previous experience, the increase steining thickness may be more than 10 percent. strata:
Bouldery strata or well resting on rock involving blasting: higher
c)
grade of concrete, higher reinforcement, use of portions, etc., may be adopted.
The recommended values given
708.2.3.4
based on
local
708.2.3.5
If
experience and specialised
in
Clause 708.2.3.2 can be further varied
accordance with decision of Engineer-in-charge.
methods
then the steining thickness
in
steel plates in the lower
of sinking,
may be
such
down method,
as, jack
are adopted
adjusted according to design and construction
requirements.
Any
708.2.3.6
variation from
dimensions as proposed
in
Clause 708.2.3.1 should be
decided before framing the proposal.
When
708.2.3.7
the depth of well below well cap
is
equal to or more than 30 m, the
thickness of the steining of the well calculated as per Clause 708.2.3
above scour
a slope of
level in
1
may be reduced
horizontal to 3 vertical such, that the reduced thickness of
the steining should not be less than required as per Clause 708.2.3 for the depth of well
upto scour level with the reduced diameter.
The reduction
in
thickness shall be done
the outer surface of the well
in
The diameter
of
inner dredge hole shall be kept uniform.
The minimum steining
steel
and the concrete grade
below scour
in
the slope portion shall be
for the
level.
Minimum development length of all the vertical steel bars minimum section as shown in the Appendix-3 (Fig. 1). The stress
same as
shall
be provided beyond the
the reduced section of steining shall also be checked.
in
708.3
Design Considerations
708.3.1
The
external diameter of the brick
25
masonry wells
shall not
exceed 6 m. Brick
IRC:78-2014 masonry wells
for
m
shall not
be permitted.
For brick masonry wells, brick not less than Grade-A having strength not less than
708.3.2
7MPa- conforming
to IS
1077
be used
shall
cement mortar not leaner than
in
1:3.
For plain concrete wells, vertical reinforcements (whether mild steel or deformed
708.3.3 bars)
depth greater than 20
the steining shall not be less than 0.12 percent of gross sectional area of the actual
in
The
thickness provided. This shall be equally distributed on both faces of the steining.
vertical
reinforcements shall be tied up with hoop steel not less than 0.04 percent of the volume per
as shown
unit length of the steining,
in
the
Appendix-3
(Fig. 2).
case where the well steining is designed as a reinforced concrete element, it shall be considered as a column section subjected to combined axial load and bending. However, the amount of vertical reinforcement provided in the steining shall not be less than 0.2 percent (for either mild steel or deformed bars) of the actual gross sectional area 708.3.4
In
of the steining.
On
minimum
the inner face, a
be provided. The transverse reinforcement
column but
with the provisions for a
in
no case
in
of 0.06 percent (of gross area) steel shall
the steining shall be provided shall
in
accordance
be less than 0.04 percent of the volume
per unit length of the steining.
The
horizontal annular section of well steining shall also
be checked
for ovalisation
moments
by any rational method taking account of side earth pressures evaluated as per Clause 708.4.
The
708.3.5
vertical
bond rods
of the cross-sectional area 1
50
mm x
1
and
50 mm. These rods
of the steining
and
shall
be
unit length of the steining.
in
brick
be encased
shall
shall
masonry
into
cement concrete
15 mix of size
The hoop
steel shall
mm wide and
in
be provided
the middle
volume per
in
a concrete band at spacing of 4
is
less.
The
horizontal
RCC
bands
mm high, reinforced with bars of diameter not less 10 mm placed at the corners and tied with 6 mm diameter stirrups at 300 mm centres, as
shall not
shown
in
708.3.6 tensile in
M
steel not less than 0.04 percent of the
times of the thickness of the steining or 3 metres, whichever
than
of
be equally distributed along the circumference
up with hoop
tied
steining shall not be less than 0.1 percent
be less than 300
the Appendix-3 (Fig.
The stresses
in
50
3).
well steining shall
and compressive stresses are
the area of reinforcement or
708.4
Stability of Well
708.4.1
The
stability
1
in
likely to
be checked
at
such
critical
sections where
be maximum and also where there
is
change
the concrete mix.
Foundations
and design
of well foundations shall be
26
done under the most critical
IRC:78-2014 combination of loads and forces as per Clause 706. The pressure on foundations shall satisfy the provisions of Clause 706.
Side earth resistance
708.4.2
The side earth resistance may be calculated as per guidelines given Appendix-3. The use of provisions IRC:45 may be used for pier well foundations 708.4.2.1
cohesionless
on
rock.
If
in
soil.
The
708.4.2.2
in
side earth resistance shall be ignored
rock strata
is
in
case of well foundations resting
such that the allowable bearing pressure
the side earth resistance
may be
taken
into
708.4.3
Earth pressure on abutments
708.4.3.1
If
is
less than
1
then
IVIPa,
account.
the abutments are designed to retain earth and not spilling
in front,
the
foundations of such abutments shall be designed to withstand the earth pressure and horizontal forces for the condition of scour depth
and 2 d sm with scour
all
around.
case of scour
In
However, where earth
708.4.3.2 front, relief
due
in
all
front of 1.27 d
around,
live
sm
load
may
from the approaches
spilling
to the spilling earth in front
may be
with approach retained
is
not
be considered.
reliably protected in
considered from bottom of well cap
downwards. 708.4.4 708.4.4. is
Construction stage Stability of the well shall also
1
no superstructure and the well
current and/or
full
is
be checked
subjected to design scour,
design earth pressure as
in
During the construction of wells
708.4.4.2 or has not
been plugged, the wells are
current upto
scour. This
full
may
for the construction
when
there
pressure due to water
the case of abutment wells.
when
likely to
result in
full
stage
tilting,
it
has not reached the founding
be subjected sliding
and
to
full
shifting.
level
pressure due to water
As a
part of the safety
during construction, this should be considered and safety of well must be ensured by suitable methods,
708.5
Tilts
708.5.1
As
However, a which
will
tilt
where
and
far
of
1
required.
Shifts
as possible, the wells in
80 and a
cause most severe
shift of
1
50
effect shall
shall
be sunk plumb without any
tilts
and
shifts.
mm due to translation (both additive) in a direction be considered
27
in
the design of well foundations.
IRC:78-2014 708.5.2
If
the actual
have to be resorted
and
tiits
shifts
exceed the above
to bring the weli within that limit.
If it
is
limits,
then the remedial measures
not possible then
its
effect
on bearing
pressure, steining stress and other structural elements shall be examined, and controlled
if
span length. The Engineer-in-charge may like to specify the maximum tilts and shifts upto which the well may be accepted subject to the bearing pressure and steining stress being within limits, by changing the span length if needed, necessary and feasible, by resorting
and beyond which the Cutting
708.6
weli will
change
to
in
be rejected irrespective of the
result of
any modification.
Edge
be strong enough and not less than 40 kg/m to facilitate sinking of the well through the types of strata expected to be encountered without suffering any damage. It shall be properly anchored to the well curb. For sinking through 708.6.1
The
rock, cutting
edge should be
708.6.2
When edge
cutting
of the outer
of the middle
stems
to
more compartments
stems of such wells
prevent rocking, as shown
Well Curb
708.7.1
The
is
shall
suitably designed.
there are two or
708 J
well
edge
mild steel cutting
well curb should
be such that
it
shall in
the
in
a well, the lover end of the
be kept about 300
Appendix-3
will offer
the
mm
above
that
(Fig. 2).
minimum
resistance while the
being sunk but should be strong enough to be able to transmit superimposed loads
from the steining to the bottom plug.
The shape and the
708.7.2 2)
may be
(Fig. 2)
dimension of the curb as given
outline
taken for guidance. The internal angle of the curb
should be kept at about 30° to 37° and
may be
'as'
in
Appendix-3
as shown
in
(Fig,
Appendix-3
increased or decreased based on
past experience and geotechnica! data.
The
708.7.3
well curb shall invariably
than
M
shall
be suitably arranged
and
in
be
in
reinforced concrete of mix not leaner
25 with minimum reinforcement of 72 kg/cum excluding bond rods. The to
prevent spreading and
splitting of
In
case blasting
is
anticipated, the inner faces of the well curb shall
protected with steel plates of thickness not less than 10 If
it
dia
mild
upto the top of the well
to
6
mm
for that
increased height.
In
any case,
more than 3 metres unless there
this extra height of the
a specific requirement.
The
such a case should be provided with additional hoop reinforcement of 10
mm
steel should in
mm
be
desired to increase the steel lining above the well curb then the thickness
is
can be reduced
curb
the curb during sinking
service.
708.7.4
curb.
steel
not be
steel
height of 3
m
or deformed
bars at
into the well steining
150
mm
above the 28
is
centres which shall also extend curb. Additional reinforcement
upto a
above
this
iRC:78-2014 height upto two times the thickness of steining should be provided to avoid cracking arising out of
sudden change
708.8
Bottom Plug
708.8.1
The bottom plug
lower than 300
bottom plug,
shall
it
be ensured that
3
fill-up all cavities.
still
wells
and the top
1
50
shall
shown
shall
be kept not
the
Appendix-3
in
edge. Before concerting the
inside faces
have been cleaned thoroughly.
bottom plug
shall
its
in
level of the cutting
have a minimum cement content
mm to permit easy flow of concrete through termie to be
laid in
one continuous operation
it
shall
colcrete, e.g., concrete
ail
any dewatering
is
if
is
till
dredge hole
is
used, the grout mix shall not be
be ensured by suitable means, such
that the grout filis-up
708. 8.4
as, controlling the rate of
interstices upto the top of the plug.
required
it
shall
be carried out
after 7
days have elapsed
bottom plugging.
708.9 708.9.1 with
in al!
to curtailment of plate.
For under water concreting, the concrete shall be placed by tremie
case grouted
in
leaner than 1:2 and
after
due
water condition and the cement content of mix be increased by 10 percent.
708.8.3
pumping
of about
Concrete
to required height.
under
be below the
shall
330 kg/m and a slump
filled
be provided
shall
The concrete mix used
708.8.2
place
the effective section
the centre above the top of the curb as
in
A suitable sump
(Fig. 2).
of
mm
in
Filling
The
the Well
of the well,
filling
if
considered necessary, above the bottom plug shall be done
sand or excavated material free from organic matter.
708.10
Plug over
708.10.1
A 300
708.11
Weil
708.11.1 the active
Filling
mm thick plug of M
15 cement concrete shall be provided over the
filling.
Cap
The bottom of well cap shall be laid as low as possible but above the LWL in channel. Where the bed level is higher than LWL the bottom of well cap may be
suitably raised.
708.11.2
As many
longitudinal bars
anchored
into the well cap.
708.11.3
The design
of the well
cap
as possible coming from the well steining
shall
be based on; any accepted
considering the worst combination of loads and forces as per Clause 706.
29
rational
shall
be
method,
IRC:78-2014 708.12
Floating Caissons
708.12.1
Floating caissons
They should have
at least 1.5
considered necessary,
very soft strata,
708.12.2
of steel, reinforced concrete or
metres free board above the water
any suitable
level
material.
and increased,
if
is
a possibility of caissons sinking suddenly owing to
likely to result
from lowering of caissons, effect of waves, sinking
in
reasons, such as, scour in
may be
case there
etc.
Well caissons should be checked for
stability
against overturning and
capsizing while being towed, and during sinking, due to the action of water current,
wave
pressure, wind, etc.
708.12.3
The
proper shear transfer at the interface
708.13
be considered as part of foundation unless
floating caisson shall not is
ensured.
Sinking of Weils
The
be sunk true and vertical. Sinking should not be started till the steining has been cured for at least 48 hours. A complete record of sinking operating including tilt and shifts, kentledge, dewatering, blasting, etc. done during sinking shall be maintained. 708.13.1
well shall as far as possible
may be
For safe sinking of wells, necessary guidance in
taken from the precautions as given
Appendix-4,
708.14
Pneumatic Sinking of Wells
708.14.1
Where sub-surface data
necessary
to
indicate the
need
for
pneumatic sinking,
decide the method and location of pneumatic equipment and
its
it
will
be
supporting
adapter.
708.14.2
In
case
if
concrete steining
restricting the tension in
concrete which
For the circular wells, the tension
in
provided,
is
will
steining
it
shall
be rendered
air tight
by
not exceed 3/8 th of the modulus of rupture.
may be
evaluated by assuming
it
to
be a
thick
walled cylinder.
708.14.3 against the
708.14.4
The uplift
steining shall
force and,
Compressed
shall
Air".
It
at different sections for
of the
pneumatic equipment, safety of personnel
comply with the provisions of is
any possible rupture
necessary, shall be adequately strengthened.
The design requirements
and the structure in
if
be checked
IS
4138 "Safety Code
desirable that the height of the working
chamber
caissons should not be less than 3 metres to provide sufficient head room
30
in
for
Working
a pneumatic
when
the cutting
IRC:78-2014
embedded a short distance below the excavated level and in particular to allow blowing down. The limiting depth for pneumatic sinking should be such that the depth
edge for
is
below normal water
of water
sinking
is
proposed should not exceed 30
level upto
which pneumatic
.
Sinking of Wells by Resorting to Blasting
708.1 5 Blasting for
proposed foundation
level to the
may be employed
with prior approval of competent authority to help sinking of well
breaking obstacles, such as, boulders or for levelling the rock layer for square seating of
wells. Blasting
may be
resorted to only
when
other methods are found ineffective.
FOUNDATION
709 PILE 709.1
General
709.1.1
Piles transmit the load of a structure to
competent sub-surface
by the
strata
resistance developed from bearing at the toe or skin friction along the surface or both. piles
may be
709.1.2
required to carry
The construction
uplift
and
The
loads besides direct vertical load.
lateral
of pile foundation requires a careful choice of piling
system
depending upon subsoil conditions and load characteristics of structures. The permissible limits of total
and
differential settlement,
unsupported length of
pile
under scour and any
other special requirements of project are also equally important criteria for adoption.
709.1.3
Design and construction
be taken from
IS
2911 subject
:
For design and construction of piles guidance
to limitations/stipulations given in this code.
may
Appendix-5
gives the design formulae and their applicability.
709.1.4
For piles
streams,
in
creeks,
rivers,
etc.,
the following criteria
may be
followed:
i)
Scour conditions are properly established.
ii)
Permanent level. In
strata.
be provided
a)
soft soil or soil having
The minimum thickness
in
in
cases given below. The
While constructing the
pile
maximum
be 6
for the
full
depth of
mm
minimum thickness
liner shall
scour
aggressive material,
be used
of liner should
land, steel liners of
which following situations
sandy
at least upto
steel liner of sufficient strength shall
For bridges located
to
be provided
case of marine clay or
permanent such
steel liner should
of 6
be provided up
to
mm
shall
depth up
prevail.
foundation through very soft clay (N < 3) ,very loose
strata (N < 8), bouldery formation
31
and artesian conditions, wherein the
IRC:78-2014 wails of boreholes cannot be stabilized by bentoniie circulation.
Where sewage leakage
b)
common phenomenon
is
as well as sites with
aggressive soil/water environment
709.1 .5
Spacing of piles and tolerances
709.1.5.1
Spacing of piles
Where
a)
pier
is
supported on multiple
solid pile cap, the
connected by frame structure or by
piles,
spacing of piles should be considered
of the ground, their behavior
in
relation to the nature
in
groups and the execution convenience. The
spacing should be chosen with regard to the resulting heave or compaction and
should be wide enough to enable the desired number of piles to be installed to the correct penetration without
damage
to
any adjacent construction or
to
the piles themselves.
For land bridges, pier may be supported on single large to
accommodate
to location of piers pile in
as weil as having strength as required by the design. The
such case. Alternatively, to pier
having diameter sufficiently
construction tolerances of pile installation with reference
should be designed to cater for the
connected
pile
pile shaft
cap which
is
maximum
eccentricity of vertical ioad
can be continued
designed
to
to act
accommodate
as a pier and get
the eccentricities due
to construction tolerances.
The
size of a
cap carrying the load from the structure
effective length of a
The spacing
ground beam,
of piles
will
friction piies,
heads, or the size and
influence type, size and spacing of piles.
be determined by many aspects mentioned above. The working
rules which are generally,
For
may
to the pile
though not always, suitable, are as follows:
the spacing centre should not be less than the perimeter of the pile or
for circular pile, three
times the diameter. The spacing of piles deriving their resistance
mainly from end bearing
may be reduced
but the distance between the surfaces of the
shafts of adjacent piies should be not less than the least width of the piles. 709. 1.5.2
Permissible tolerances for piles shall he as under: i)
For vertical piles 75
mm
at piling platform level
and
tilt
not exceeding
150; ii)
709.1.6
For raker piles tolerance of
The maximum rake
to
in
be permitted
bored
i)
1
in
6 for
ii)
1
in
6 for driven cast-in-situ
all
1
25.
in piie
piles;
piies;
32
and
shall not
exceed the
following:
1
in
IRC:78-2014 1
iii)
in
4
for
The minimum diameter
709.1.7
beyond the water zone and
709.1 .8
The
in
estimated from the
superimposed loads,
load,
piles.
for bridges
it
for river/marine bridges.
maximum
and pile capacity
at pile
cap
level,
settlement expected at two foundations for the dead
load and scour effect.
live
For bridges
on land, the diameter may be reduced upto 750 mm.
between two successive foundations taken
clayey soils shall be accounted
of preliminary design,
m
be 1.0
shall
Settlement, differential settlement
Differential settlement
may be
Precast driven
absence
for. In
The increase
in
settlement with time
of detailed calculations, for the
purpose
can be taken as not more than the maximum settlement of any of
the two foundations.
The
differential
settlement shall be limited depending upon the following functional and
structural considerations:
a)
Functionally, acceptable differential settlement piers shall not
as specified b)
be greater than
in
1
in
400
of the
between two neighboring
span
to
ensure
riding comfort,
Clause 706.3.2.1.
The allowable settlement
of a single pile considered for estimating the pile
capacity shall be arrived from correlation of the settlement of pile group to that of single pile, as per c)
It
is
Clause 709.3.4.
further provided that the working load capacity of pile
based on the
sub-clause b) shall not exceed 40 percent of the load corresponding to the settlement of 10 percent of pile diameter ultimate load capacity
709.1
is
water cement
ratio,
slump
shall
safety factor of 2.5 on
ensured).
For both Precast and cast-in-situ
.9
(i.e.
piles,
the values regarding grade of concrete,
be as follows:
Concrete Cast-in-situ by
Precast Concrete
Tremie Grade Min.
of concrete
cement contents
Max. W.C.
ratio
Slump (mm)
NOTE
:
i)
M
35
M35
400 kg/m 3
400 kg/m 3
0.4
0.4
150-200
50-75
For improving resistance to penetration of harmful elements from
33
soil
use of mineral
IRC78-2014 admixtures (flyash,
fume,
silica
standards) and as per IRC:112 ii)
is
GGBS
conforming to respective B!S/lnternational
recommended.
marine conditions and areas exposed
In
to action of harmful chemicals, protection
of pile caps with suitable coating such as bituminous based, coal-tar epoxy based
coating
may be
not be used
in
considered. High alumina cements,
709.2
Requirement and Steps
709.2.1
The
initial
for
not
is
and
and load
testing:
final
i)
recommended.
Design and
design of an individual
load test or by re-confirmation of actual
required,
quick setting cement) shall
marine conditions. Also when both chlorides and sulphates are present,
use of sulphate-resistant cement
initial
(i.e.
confirmation of
pile,
soil
Installation
capacity by either
its
parameters, modification of design,
adoption should pass through following steps of investigations, design
Comprehensive and detailed sub-surface
investigation
determine the design parameters of end bearing capacity,
and ii)
if
lateral
Design of
capacity of pile
and
surrounding the
soil
pile
group based on
for
piles
to
friction
capacity
for specified
bearing
pile.
i)
above
strata.
iii)
Initial
Initial
load testing: load test on pile of same diameter as design pile for direct confirmation
of design.
The
initial
load test
is
a part of the design process confirming the expected
properties of bearing strata iv)
709.2.2
Steps
The steps
ii)
and
for
iii)
and the
pile capacity.
should be repeated for different types of strata met at
design and confirmation by tests are given below:
parameters assumed
i)
Sub-soil exploration to reconfirm
ii)
Provide for the required design capacity of
number and diameter iii)
site.
of piles
in
soil
pile
in
the design.
group based on tentative
a group.
The allowable total/differential settlement of single
pile
should be based on
the considerations as per Clauses 709.1 .8 and 709.3.4. Capacity of single pile is to
be based on
static
This step along with step iv)
Structural design of piles.
v)
Initial
ii)
load test as mentioned
formula considering ground characteristics.
may be
in
34
iterative.
Clause 709.2.1
iii)
is
for axial load capacity,
IRC:78-2014 including uplift capacity,
the design
pile.
The
required,
if
testing shall
on
trial
same diameter as procedure laid down in
piles of the
be done as per the
IS:2911, Part-IV. This load test shall be conducted for not less than
times the design load. The deriving strength from test
can be performed
for the
vi)
If
the
socketed
initial
end bearing
capacity, another
two load tests
minimum
The number
of
if it
of the three shall
initial
tests shall
For abutment, piles
it
is
is
shall
on
friction,
and
desired to take benefit of the higher
be carried out
to confirm the earlier
be considered as
initial
load test value.
be determined by the Engineer-in-charge
taking into consideration the bore log
and abutment. The
piles without relying
load
piles in rock.
calculated by static formula, and
709.2.3
The maintained
friction.
load test gives a capacity greater than 25 percent of the capacity
initial
value and
load test shall be cyclic load test for piles
end bearing and side for
27 2
and
soil profile.
important to consider overall stability of the structure
should also be designed to sustain surcharge effect of
embankment.
709.2.4
Routine load test
i)
Routine load test should be done at locations of alternate foundations of bridges to reconfirm or modify the allowable loads. Vertical and horizontal load tests should be properly designed to cover particular pile group. lateral load test
may be conducted on two
of routine load tests shall not of piles.
be used
The minimum number
for
of tests to
adjacent
upward
piles.
The
However, results
revision of design capacity
be conducted
is
as given below
for
confirming pile capacity.
Total
number
of Piles for the Bridge
Minimum No.
of Test Piles
Upto 50
2
Upto150
3
Beyond 150
2 percent of
rounded
NOTE:
The number
of tests
may be
to
total
next
judiciously increased
piles
(fractional
number
higher integer number).
depending upon the
variability of
foundations strata.
ii)
Permissible Over Load
While conducting routine test on one of the
35
pile
belonging to a
pile
group, if
IRC:78-2014 the pile
is
found to be deficient (based on the settlement
times the design load) an overload upto
may be
0 percent of the reduced capacity
allowed.
For a quick assessment of
iii)
1
criteria at 1.5
conducted
piie capacity, high-strain
dynamic
strain
dynamic
be used
tests shall not
revision of design capacity of pile. Detailed guidelines are at
These methods can be
1.
To have a
iv)
defects
good idea about the
like
voids,
Appendix-7 Part
Resistance
pile
Appendix-5 should be
for load
combination
For purpose of these Clauses the following definitions
b)
Granular
soil (clay soil
c)
or plastic
silt
will
m
integrity
are
tests
references are at
I
of
Clause 706.1.1,
criteria
as per Clause 709.1 .8.
apply.
S u < 0.25 MPa);
with
(sand, gravel or non-plastic
< 50 blows/0.3
and construction
followed. For calculating capacity of pile group,
Clauses 709.3.3 and 709.3.4 and the allowable settlement
Cohesive
Appendix-7
loads
For calculating designed capacity of
a)
upward
2.
709.3.1
refer
pile
etc.,
guidelines and
Detailed
Geotechnical Capacity of Pile
of
quality of concrete
discontinuities,
709.3
to vertical
for
followed.
fairly
extensively conducted.
recommendation
may be
after establishing co-relations using the results of load tests.
However, results of the Part
tests
silt
with
N (average
within layer)
(50 blows/30 cms);
Intermediate Geomaterial Cohesive: e.g. clay shales or mudstones with 0.25
Cohesion
less: e.g. granular
tills,
MPa
(2.5 tsf) <
granular residual soils
Su <
N>50
2.5
MPa.
blows/0.3
m
(50 blows/30 cm); d)
Rock: Cohesive, Cemented Geomaterial with Su > 2.5MPa (25
qu> 709.3.2
computed on the basis
of
MPa.
factor of safety
on ultimate
axial capacity
formula shall be 2.5 for load combination
piles in rock, factor of safety shall
I
of
as stipulated
in
Clause 706.1 .1
for piles in soil.
For
be 3 on end bearing component and 6 on socket
side resistance component, for load combination limits
or
Factor of Safety
The minimum static
5.0
tsf)
Appendix-5.
36
I
of clause 706.1.1 subject to further
IRC:78-2014 Capacity of piles/group action
709.3.3
The
axial capacity of a
group of
the capacity of individual piles multiplied by the
Factor
i)
may be
be determined by a factor
piles should
taken as
1
in
number
of
minimum 3 times diameter
For
ii)
pile
groups
in
clays, the
pile
be applied
to
of piles of the group.
case of purely end bearing
spacing of 2.0 times the diameter of
to
and
piles having
minimum
having spacing
for frictional piles
of pile.
group capacity
shall
be lesser of the
following:
a)
Sum
b)
The capacity of the group based on block failure concept, where the ultimate
of the capacities of the individual piles
in
the group.
load carrying capacity of the block enclosing the piles
in
estimated.
Settlement of pile group
709. 3. 4
of a pile
The capacity of a pile group is aiso governed by settlement criterion. Settlement group may be computed on the basis of following recommendations or by any other
rational
method.
709.3.4.
1
709. 3. 4. 2
Settlement of pile group
The settlement
of a pile
group
method
of installation of piles.
may be
used.
The settlement
is
one
third of the pile length
sands
Methods given of
shape and size
affected by the
group of
the load carried by the pile group at
in
is
piles in
upwards from the
Settlement of pile group
The settlement
of pile
group
in
Peck Approach which assumes soil
The
2 (vertical)
:
in
method
raft
that
located
toe for friction piles. For end bearing piles raft
placed at the toe of the
pile
group.
clays shall be evaluated using Terzaghi and
homogeneous
that the load carried by the pile
is
group
is
third of the pile length
assumed
to
spread
transferred to the
upwards from the
into soil at
a slope of
(horizontal).
The settlement
for equivalent footing shall
be evaluated
(Part-ll).
709. 3.4.4
rational
and
clays
load under the equivalent footing 1
any other
sands can be calculated by assuming
pile
through an equivalent footing located at one
pile toe.
(Part-ll) of
transferred to the soil through an equivalent
the settlement can be calculated by assuming the
709. 3. 4. 3
8009
IS
in
of group, length, spacing
Settlement of pile group
in
rock
37
in
accordance with
IS
8009
IRC:78-2014 Settlement of piles founded value of
modulus
in-situ
709.3.5.
The
1
may be computed as
rock
of rock
Resistance
709.3.5
in
per IS 8009 (Part
considering the
II)
mass.
to lateral
loads
ultimate lateral resistance of a group of vertical piles
passive pressure acting on the enclosed area of the calculated over an equivalent wall of depth equal to
taken as the
Such passive pressure may be
piles.
6D and
may be
width equal to L + 2B.
where
D
=
Diameter of
L =
Length between outer faces of direction of
B=
lateral
resistance of individual piles.
modulus
combination percent of
I
For single
pile
on ultimate
The safe
pile
piles,
point of
709.3.6
in
of lateral
depends on the
as well as the structural
modulus as recommended
lateral load resistance in load
is
not required.
confirmation of capacity of group by load testing
is
not required.
head condition
fixity
may be performed
for piles
directly, or
method given
Piles
in
accordance with IS:291 1 Testing
in
.
having free standing shaft above scour level upto the
pile
may be
pile
in
it
will
above
be necessary is
to drive
free to deflect.
The
calculated from deflection
a larger diameter deflection at scour
measured
at higher
acts as structural cantilever from the point of
can be taken from the analysis performed
Uplift
1
soil
sum
other load combinations
the horizontal load test
may be measured
simplified
used
resistance of individual pile
same. For safe
diameter. Checking of deflections
pile
for free
709.3.6.
resistance shali be 2.5.
lateral load
to calculate the
(ground) level assuming that the
The
plan parallel to the direction
resistance of pile-group must not exceed the
casing upto scour level so that the test
like,
lateral
cap. For conduction test at scour level,
level
in
of Clause 706.1.1, the deflection at scour level shall not be greater than 1.0
For a group of vertical
be
group
Appropriate rational method of analysis using
may be used
by IS:2911
shall
pile
of horizontal sub-grade reaction of the foundation material
rigidity of pile.
plan perpendicular to
in
movement.
factor of safety
The safe
709.3.5.2
group
pile
movement.
Width between outer faces of of
The minimum
pile
for the
fixity.
design or calculated by
IS:2911.
load carrying capacity
may be required to
resist uplift forces of
foundations subjected to large overturning
underpasses subjected
permanent or temporary nature when
moments
to hydrostatic uplift pressure.
38
or as anchorages
in
structures,
IRC:78-2014
The
709.3.6.2
ultimate
uplift
may be
capacity
calculated with the expression of shaft
and applying a
resistance/skin friction only, of the static formulae for compression loads
reduction factor of 0.70 on the same.
from 0.3
m
case of
In
rock, the socket length shall
depth to actual depth of socket. The weight of the
as acting against
also be taken
pile shall
out test shall be conducted for verification of
uplift. Pull
be measured
uplift
capacity.
Factor of (2.5/0.7) = 3.5 on the ultimate strength shall be used. 709.3.6.3
The
uplift
-
the
-
the
capacity of pile group
is
lesser of the two following values:
sum of the uplift resistance of the individual piles in the group, and sum of shear resistance mobilised on the surface perimeter of
group plus the effective weight of the
soil
and the
piles
enclosed
the
in this
surface perimeter. 709.3.6.4
Piles should
be checked
with other co-existent forces,
709.3.6.5
adequacy against
for structural
uplift
forces together
any.
if
The minimum factor of safety on
ultimate
uplift
load calculated on the aforesaid
basis shall be 2.5. Piles subjected to
709.3.7
When
a
soil
stratum through which
compresses due load
is
downward drag
to
its
own
generated along the
may be assessed on i)
pile shaft
has penetrated
into
an underlying hard stratum
weight, or remoulding, or surface load etc., additional vertical
such stratum. Such additional load coming on
pile shaft in
the following basis:
In
the case of pile deriving
of
downward drag
its
capacity mainly from
may be
force
compressible
case of
of
downward drag
force
may be
piles,
compressible
than the number of piles forces, the iv)
same
This reduction
in
considered as 0.5 times undrained pile shaft
embedded
in
the drag forces shall also be calculated considering
the surface area of the block in
embedded
soil.
For a group of
embedded
pile shaft
capacity mainly from end bearing, the value
pile deriving its
shear strength multiplied by the surface area of
iii)
the value
soil.
In
compressible
friction,
taken as 0.2 to 0.3 times undrained
shear strength multiplied by the surface area of
ii)
pile
in
shall
in
(i.e.,
perimeter of the group times depth)
In
the event of this value being higher
soil.
the group times the individual
be cosidered
capacity of
pile is in
39
in
the design.
the ultimate capacity
downward drag
IRC:78-2014 709.4
Structural Design of Piles
709.4.1
A pile
from structure to
which
it
as a structural
to soil.
may be
The
member
pile shall
subjected
to,
shall
have
sufficient strength to transmit the load
also be designed to withstand temporary stresses,
if
any,
such as, handling and driving stresses. The permissible
stresses should be as per IRC:112.
The
test pile shall
709.4.2
The
be separately designed
piles
may be designed
their structural capacity
potential liquefaction level,
in
if
piles
on land,
if
is
due
to
upto scour level and upto for.
shaft can be calculated as described
in pile
the pile group
may be considered as having fixed head force may be distributed equally in all piles 709.4.4
pile
applicable, should be duly accounted
moments
the load effects and
all
self load of pile or lateral load
on the portion of free
etc.
For the horizontal loads the
Clause 709.3.5.2. For
taking into consideration
examined as a column. The
earthquake, water current force,
709.4.3
to carry test load safely to the foundation.
provided with
rigid
cap, then the piles
in
appropriate direction for this purpose. Horizontal
in
a group with a
rigid pile
cap.
Reinforcements for cast-in-situ piles
The reinforcements
in pile
should be provided complying with the requirements of IRC:112,
as per the design requirements. The area of longitudinal reinforcement shall not be less than 0.4 percent nor greater than 2.5 percent of the actual area of cross-section
in all
cast-
The clear spacing between vertical bars shall not be less than 100 mm. Grouping of not more than two bars together can be made for achieving the same. Lateral reinforcement shall be provided in the form of spirals with minimum 8 mm diameter steel, spacing not more than 150 mm. For inner layer of reinforcement, separate links tying them to each other and to outer layers shall be provided. in-situ
concrete
709.4.5
piles.
For pre-cast driven
of IRC: 11 2, for resisting stresses
piles,
due
the reinforcement should comply with the provision
to lifting, stacking
transmitted from the superstructure and bending longitudinal reinforcement shall not
due
to
and
transport,
any
any secondary
uplift
effects.
or bending
The area
of
be less than the following percentages of the cross-
sectional area of the piles: a)
For piles with a length less than 30 times the least width
b)
For piles with a length 30 to 40 times the least width
c)
For piles with a length greater than 40 times the least width -2 percent.
709.5
Design of
Pile
709.5.1
The
caps
pile
- 1
- 1
.5
.25 percent;
percent; and
Cap shall
be of reinforced concrete of size fixed taking
40
into
IRC:78-2014 consideration the allowable tolerance as shall
cap
in
A minimum
Clause 709.1.5.2.
be provided beyond the outer faces of the outer-most
is in
piles in the group.
minimum 80
contact with earth at the bottom, a levelling course of
cement concrete
709.5.2
be
pile shall
709.5.3
shall
top of the pile shall project 50
fully
anchored
mm
into the pile
cap and reinforcements of
cap.
in pile
Marine conditions or
in
quick setting cement shall not be used
Such a
pile
by using
areas exposed
to the action of harmful
cap can be considered as
rigid.
&
tie'
method. which
at
cap designed by
'strut
All
it
&
The
pile
in pile
no longer required.
tie'
cement
cap should be 1.5 times the diameter of
reinforcement
is
chemicals, i.e.
marine constructions.
of pile
beyond the point pile
in
The minimum thickness 'strut
the pile
mm thick plain
the pile cap shall be protected with a suitable anti-corrosive paint. High alumina
709.5.4
If
mm
150
be provided.
The
In
offset of
cap may be designed as cap It
have
shall
full
pile.
thick slab or,
anchorage capacity
should be specially ascertained for
method. Where large diameter bars are used as main
reinforcement, the corners of pile caps have large local cover due to large radius of bending of
main bars. Such corners
709.5.5
Casting of
functionally
it
is
shall
pile
be protected by
cap should be
at
locally placing small
level
higher than water level unless
required to be below water level at which time sufficient precautions
should be taken to dewater, the forms to allow concreting
709.6
diameter bars.
I
dry conditions.
Important Consideration, Inspection/Precautions for Different Types of Piles
709.6.1
Driven cast-in-situ piles
709.6.1.1
Except otherwise stated
(Part 1/Section
709.6.1.2
in this
code, guidance
is
to
be obtained from
IS
2911
I).
The
pile
shoes which may be
either of cast iron conical type or of mild steel
flat
type should have double reams for proper seating of the removable casing tube inside the
space between the reams.
709.6. 1.3 is
Before
commencement of pouring
no ingress of water
in
it
should be ensured that there
the casing tube from the bottom. Further adequate control during
withdrawal of the casing tube inside the casing tube at
of concrete,
all
is
essential so as to maintain sufficient
stages of withdrawal.
41
head of concrete
IRC:78-2014 Concrete
709.6.7.4
designed top
level of pile,
final set
or after 3 days.
709.6.2
Bored
709.6.2.
1
sufficiently
which
is
The
be cast upto a minimum height of 600
piles shall
in
which
shall
be stripped
off to
obtain
sound concrete
above the
either before
cast-in-situ piles
mud, such
drilling
as, bentonite
above the surrounding ground water
suspension level to
being penetrated throughout the boring process
709.6.2.2
mm
The bores must be washed by
shall
be maintained
ensure the
until
stability of
at a level
the strata
the pile has been concreted.
fresh bentonite solution flushing to ensure
clean bottom at two stages prior to concreting and after placing reinforcement. 709. 6. 2. 3
Concreting of piles
Concreting shall be done by tremie method.
In
tremie method the following requirements are
particularly applicable.
a)
When be
concreting
is
carried out for a pile, a temporary casing should
installed to sufficient depth,
drop from the sides of the hole
temporary casing
under
drilling
is
so that fragments of ground cannot into the
concrete as
not required except near the top
it
is
placed.
when
The
concreting
mud.
b)
The hopper and tremie should be a
c)
Tremie diameter of minimum 200
leak proof system.
mm
shall
be used with 20
mm
diameter
down aggregate. d)
The
first
charge of concrete should be placed with a
down the tube ahead
of
it
sliding plug
pushed
or with a steel plate of adequate charge to prevent
mixing of concrete and water. However, the plug should not be
the
left in
concrete as a lump. e)
The tremie pipe should always penetrate
well into the concrete with
adequate margin of safety against accidental withdrawal of the tremie should be always f)
The
pile
full
being entrapped within the
All
The
of concrete.
should be concreted wholly by tremie and the method of deposition
should not be changed part
g)
pipe.
an
way up
the
pile, to
prevent the laitance from
pile.
tremie tubes should be scrupulously cleaned after use.
42
IRC:78-2014 h)
As tremie method need
i)
to
of concreting
is
not under water concreting, these
is
no
add 10 percent extra cement.
Normally concreting of the piles should be uninterrupted.
In
the exceptional
case of interruption of concreting; but which can be resumed within 2 hours, the tremie shall not be taken out of the concrete. Instead
be raised and lowered
or
1
shall
it
from time to time to prevent the concrete
slowly,
form setting. Concreting should be resumed by introducing a concrete with a slump of about 200
mm
for
richer
little
easy displacement of the
partly set concrete. If
the concreting cannot be
placed, the pile so cast j)
resumed before
may be
set of concrete already
rejected or accepted with modifications.
In
case of withdrawal of tremie out of the concrete, either accidentally or
to
remove a choke
following
in
the tremie, the tremie
manner to prevent impregnation
top of the concrete already deposited k)
final
The tremie
penetration
little
introduced
mm
shall
should be
pushed in its
filled in
to the old
scum
lying
in
When
vermiculite plug/surface retarders should be
the tremie which
will
is
mm to
175
push the plug forward and
steps making fresh concrete tremie
on the
concrete with very
of the tremie displacing the laitance/scum.
further
way.
A
of laitance or
the
in
the bore.
be gently lowered on initially.
reintroduced
the tremie. Fresh concrete of slump between 150
in
emerge out
in
may be
The tremie
will
will
be
sweep away laitance/scum
may
buried by about 60 to 100 cm, concreting
be resumed. I)
The
'L'
bends
in
the reinforcements at the bottom of the piles should not be
provided to avoid the formation of soft toe.
Removal of concrete above
709. 6. 2. 4
It
is
desirable that the concrete above cut-off level
The concrete may be removed manually removal of concrete helps level
in
is
removed before the concrete
or by specially
preventing the
damages
made
of the
is
bailer or other device.
good concrete below the
set.
Such
cut-off
which results from chipping by percussion method.
The removal on the
(-)
rammer In
cut-off level
of concrete
side.
On
can be within ± 25
mm from the specified
cut-off level preferably
removal of the such concrete, the concrete should be compacted with
with spikes or
case the concrete
it
shall
is
not
be vibrated.
removed before
setting, a
groove
shall
perimeter by rotary equipment before chipping by percussion method.
43
be made on outer
IRC:78-2014 Driven precast concrete piles
709.6.3
709.6.3.
1
Except otherwise stated
code, guidance
in this
is
to
be obtained from
IS 2911
(Part I/Section 3).
709.6.3.2
design requirement
may be
is
known
cast to avoid lengthening of piles as far as possible.
and approved
may be used
concrete at top of original
to permit concreting
only after the method of splicing
pile shall
be cut down
is
between the
in
to sufficient length to avoid spelling
tested
bars.
During installation of
piles,
the
final
General
710.1.1
In
case of
100 blows.
last
plain concrete substructure, surface reinforcement at the rate of
2
2.5 kg/m shall be provided shall not
set or penetration of piles per blow of
SUBSTRUCTURE
710 710.1
by heat
neighboring reinforcement shall be such as
should be checked taking an average of
such bars
unavoidable, the
be joined by welding or by mechanical couplers. The
of welding. Location of mechanical couplers
hammer
When
earlier.
longitudinal reinforcement shall
709.6.3.3
length of pile as per
with reasonable degree of accuracy. Extra length of pile
splicing for lengthening of steel
The
may be adopted when
This type of piles for bridges
in
each
direction,
exceed 200 mm.
In
i.e.,
both horizontally and
case of substructure
in
vertically.
Spacing of
severe environment (as per
Clause14.3.1 of 112 or as per clause 302.6 table 5 of IRC:21) the surface reinforcement
can be dispensed
with,
be so proportioned 710.1
.2
to
if
specifically allowed but the
keep the stresses only up
to
dimension of the substructure should
90 percent of the allowable stress.
For the design of substructure below the level of the top of bed block, the
live
load impact shall be modified by the factors given below:
i)
For calculating the pressure at the bottom surface of the pier/abutment cap
ii)
For calculating pressure on the top 3
0.5
m
substructure below pier/abutment cap
44
of
Decreasing uniformly from 0.5 to zero
IRC:78-2014 For calculating the pressure on the portion
iii)
of the substructure, at
more than 3
m
Zero
below
the pier/abutment cap.
Structures designed to retain
710.1.3
pressure calculated
in
accordance with any
earthfill
shall
rational theory.
be proportioned
No
structure shall, however, be
designed to withstand a horizontal pressure less than that exerted by a
kg/m
3 ,
in
addition to the live load surcharge,
The
71 0.1 .4 in
Appendix-6
backfill
Piers
710.2.1
Piers
weighing 480
any.
behind the wing and return walls shall conform to the specifications
in
stream and channel should be located
clearance requirements and give a
in
fluid
with provision for proper drainage.
710.2
piers should
if
to withstand
be placed
other locations,
like,
minimum
to
meet navigational
interference to flood flow.
parallel with the direction of
stream current
In
general,
at flood stage. Piers
viaducts or land spans should be according to the requirement
of the obstacles to cross over.
Where necessary,
710.2.2
waters as given
in
adopted
Pier for
be provided
at both
ends with
suitably
shaped cut
IRC:6. However, cut and ease water where provided shall extend upto
affluxed H.F.L. or higher,
710.2.3
piers shall
if
may be
masonry
stresses as provided
necessary, from consideration of local conditions, in
piers. in
like,
waves,
PSC, RCC, PCC or masonry. Only solid section should be The design of masonry piers should be based on permissible
IRC:40.
71 0.2.4
The thickness
710.2.5
The multi-column
of the walls of hollow concrete piers should not be less than
mm
thickness.
Unbraced
multiple
performance of similar structures of
such bracing, when adopted,
710.2.6
in
column
piers
may be
shall
minimum
allowed depending upon the
similar conditions of river.
However, type and spacing
be predetermined.
Piers shall be designed to withstand the load and forces transferred from
the superstructure and the load and forces on the pier self-weight. In general, pier
710.2.7
300 mm.
piers of bridges across rivers carrying floating debris, trees
or timber should be braced throughout the height of the piers by diaphragm wall of
200
etc.
In
case of
may be
solid,
pier consisting of
itself,
apart from the effect of
its
hollow or framed structures.
two or more columns, the horizontal forces
at
the bearing be distributed on columns as required by appropriate analysis.
71 0.2.8
If
the piers consist of either multiple piles or trestle columns spaced closer
45
IRC:78-2014 than three times the width of piles/columns across the direction of flow, the group shall 1
be treated as a
solid pier of the
.25 for working out pressure
IRC:6.
If
due
to
same
overall width
and the value
water current according
to relevant
K taken as
of
Clause 213.7 of
such piles/columns are braced then the group should be considered a
solid pier
irrespective of the spacing of the columns.
Hollow piers
710.2.9
shall
be provided with suitably located weep-holes of 100
mm
diameter for enabling free flow of water to equalise the water levels on inside and outside; of flood/tide water.
The
considering rate of
rise/fall
expected
water-head/wave pressure and
differential
calculations, a
minimum
The
71 0.2.1 0
difference of 1.5
m
in
silt
pressure.
reinforcement of the walls of hollow circular
lateral
In
be checked
absence
for
of detailed
water levels on two sides shall be assumed.
than 0.3 percent of the sectional area of the walls of the distributed
pier walls should
pier.
RCC
pier shall not
be less
This lateral reinforcement shall be
60 percent on outer face and 40 percent on inner face.
710.3
Wall Piers
710.3.1
When
be checked as a
The
710.3.2
the length of solid pier
is
more than
four times
its
thickness,
it
shall also
wall.
reinforced wall should have
minimum
vertical reinforcement
equal to 0.3
percent of sectional area.
For eccentric axial load, the wall should be designed for axial load with
710.3.3
moment. The moments and the horizontal forces should be account the dispersal by any rational method.
The
710.3.4 vertical
vertical
reinforcement
is
distributed taking into
reinforcement need not be enclosed by closed stirrups, where not required for compression. However, horizontal reinforcement
should not be less than 0.25 percent of the gross area and open links (or S-loops) with hook placed around the vertical bar should be placed at the rate of 4 links
When
710.3.5
walls are fixed with superstructure, the design
in
one running metre.
moment and
axial load
should be worked out by elastic analysis of the whole structure.
710.4
Abutments
710.4.1
The abutments
dimensioned
carry superstructure from
in
addition to load
one
side.
It
should be designed/
from the approach embankment.
The abutments should be designed
710.4.2 condition
to retain earth
will
to withstand earth
pressure
and forces transferred from superstructure.
46
In
in
normal
addition,
any
IRC:78-2014 load acting on the abutment
710.4.3
case of
In
spill
including self-weight,
itself,
to
is
be considered.
through type abutment, the active pressure calculated on the
width of the column shall be increased by 50 percent where two columns have been provided
and by 100 percent where more than two columns have been provided. 710.4.4
abutments and abutment columns
All
surcharge equivalent to 1.2 not be increased as
m
height of earth
Clause 710.4.3
in
for
The
fill.
shall
be designed
for a
effective width of the
surcharge effect when
spill
load
live
columns need
through abutment
is
adopted.
Abutment should also be designed
710.4.5
for
water current forces during 'scour
all
round' condition.
The abutment may be
710.4.6
abutment may be either through type. For
spill
of plain or reinforced concrete or of masonry.
The
box type or
spill
solid type, buttressed type, counterfort type,
out as for piers. Counterfort type abutment
be and the slab 710.4.7
may be designed as
Fully earth
retaining
may be
treated as
T
submerged
unit
weight of
The weight
710.4.8 the weight
710.4.9
may be In
front of the
soil
of earth
considered
case of
abutment
spill
is
if
carried
may
or L type as the case
continuous over counterforts.
abutments should be designed considering submerged/
saturated unit weight of earth as appropriate during H.F.L. or L.W.L. condition. the
may be
through abutment, column type or wall type, analysis
where considered
filling
shall not
material on heel
the bed
is
case of footings,
be less than 1000 kg/m 3
may be
considered.
In
.
case of
toe,
protected.
through type abutment,
well protected by
In
means
it
should be ensured that the slope
of suitably
in
designed stone pitching and
launching aprons.
710.4.10
In
wall should not
than 250
710.4.11
case of abutments having counterfort, the minimum thickness of the be less than 200
front
mm and the thickness of the counterfort should not be less
mm.
In
case
of
box type abutments, weep holes
shall
be provided similar
to
hollow piers as per Clause 710.2.9.
710.5
Abutment
710.5.1
Abutment
Pier
piers
may have
to
be provided
47
at locations
where there may be a
IRC:78-2014 need of increasing waterway subsequently. The design such that
of
such abutment piers
should be possible to convert them to the similar shape as piers
it
in
shall
be
the active
channel.
For multiple span arch bridges, abutment piers shall be provided after every
710.5.2 fifth
span or
closer.
It
designed
is
the pier and arches on other side
710.6
Dirt Walls,
710.6.1
Wing
for condition that will
even
if
arch on one side of
it
collapses,
remain safe.
Wing Walls and Return Walls
walls shall be of sufficient length to retain the
roadway
to the required
extent and to provide protection against erosion.
A dirt wall shall be provided to prevent the earth from approaches spilling on bearings. A screen wail of sufficient depth (extended for at least 500 mm depth into the
710.6.2 the
to
fill)
prevent slipping of the
backfill in
case the abutment
is
of the
spill
through type, shall
be provided.
counterfort type.
710.6.4 of
may be of solid type. The return walls may be of solid The material used may be plain or reinforced concrete or masonry.
The wing
710.6.3
walls
Dirt wall/ballast wall
and screen
wall shall
or
be provided with minimum thickness
200 mm.
The wing
710.6.5
walls should be designed primarily to withstand the earth pressure
in
addition to self-weight.
The top
710.6.6
by
at least
top.
100
A drainage
mm
of the wing/return walls shall be carried to
prevent any
arrangement
abutment specified 710.6.7
The
710.6.8
In
in
at right
embankment
from being blown or washed away by
for return wall/wing wall
cantilever returns
may be
rain
over
its
provided similar to that for the
where adopted should not be more than 4 metres
long.
case of open foundations, wing and return walls should be provided with
Wing
river bridges,
of
Appendix-6.
separate foundations with a
710.6.9
soil
above the top
walls
joint at their junction with the
may be
abutment.
any suitable angle
laid at
these are normally splayed
in
plan at 45°.
The
to the
abutment.
return walls
In
may be
case of provided
angles to the abutment. Return walls shall be designed to withstand a live-load
surcharge equivalent to
1
.2
m
height of
earthfill.
48
IRC:78-2014
The box type return wall at right angles at both ends of the abutments connected type diaphragm may be adopted where found suitable. However, in such cases, no
710.6.10
by wall
reduction
the earth pressure for the design of the abutment should be considered.
in
The
top of diaphragm should slope inwards to the centre of carriageway for facilitating proper rolling of
the
embankment behind
the abutment.
on independent foundations can be suitably
Solid type of wing/return walls
710.6.11
stepped up towards the approaches depending upon the pattern of scour, conditions and
its
710.6.12
case of wing walls or return
In
profile,
local
ground
safe bearing capacity, etc. walls, the foundation shall
be taken adequately
into the firm soil.
710.7
Retaining Walls
710.7.1
The minimum thickness
710.7.2
The
any
live
of reinforced concrete retaining wall shall be
retaining walls shall
be designed
load surcharge and other loads acting on
with the general principles specified for abutments. shall
be of
solid type.
Reinforced concrete walls
pressure including
to withstand earth it,
including self-weight,
Stone masonry and
may be
200 mm.
in
accordance
plain concrete walls
of solid, counterfort, buttressed or
cellular type.
The vertical stems of cantilever walls shall be designed as cantilevers fixed at the base. The vertical or face walls of counterfort type and buttressed type shall be designed as continuous slabs supported by counterforts or buttresses. The face walls shall be securely anchored to the supporting counterforts or buttresses by means of adequate 710.7.3
reinforcements.
710.7.4
Counterforts shall be designed as
designed as rectangular beams. counterforts, there shall
In
T-beams
or L-beams. Buttresses shall be
connection with the main tension reinforcement of
be a system of horizontal and
vertical bars or stirrups to
anchor the
face walls and base slab to the counterfort. These stirrups shall be anchored as near to the outside faces of the face walls and as near to the bottom of the base slab as practicable.
and Abutment Caps
710.8
Pier
710.8. 1
The width
of the
abutment and
pier
caps
shall
i)
the bearings leaving an offset of 150
ii)
The
iii)
The space
be
mm
sufficient to
accommodate
:
beyond them,
ballast wall. for jacks to
lift
the superstructure for repair/replacement of
bearings, etc.
49
IRC:78-2014
The equipment for prestressing operations where necessary, over and above space for end block in cast in-situ cases.
iv)
v)
The drainage arrangement
vi)
Seismic arrestor,
vii)
To accommodate inspection ladders
The thickness
710.8.2
not be less than
250
of
for the
water on the cap.
provided
if
cap over the hollow
pier or
column type
of
abutment should
mm but in case of solid plain or reinforced concrete pier and abutment,
the thickness can be reduced to 200
mm.
Pier/Abutment caps should be suitably designed and reinforced to take care
710.8.3
of concentrated point loads dispersing
in
pier/abutment.
Caps
cantilevering out from the
supports or resting on two or more columns shall be designed to cater for the superstructure on jacks for repair/replacement of bearings.
The
lifting
of
locations of jacks shall be
predetermined and permanently marked on the caps.
710.8.4
In
case bearings are placed centrally over the columns and the width of
bearings/pedestals
located within half the depth of cap from any external face of the
is
columns, the load from bearings
will
be considered
columns and the cap beam need not be designed
to
have been
directly transferred to
for flexure.
The thickness of the cap over masonry piers or abutment than 500 mm. The minimum width at the top of such piers and abutments 710.8.5
shall not
of slab
be less
and girder
bridges just below the caps shall be as given below:
Span Top
in
metres
width
of
3 pier
supported spans
in
carrying
simply
m
12m
24m
0.50
1.0
1.2
1.6
piers
0.40
0.75
1.0
1.3
Exceptthe portion under bearings, the top surface of caps should have suitable
710.8.6 in
6
m
Top width of abutment and of carrying continuous spans in m
slope
m
order to allow drainage of water.
710.8.7
Reinforcement
square-root formula stated with a total steel shall
minimum
of
1
in in
Pier
and Abutment Caps where the bearing
Clause 307.1 of IRC:21, the pier caps
shall
percent steel, assuming a cap thickness of 225
be distributed equally and provided both at top and bottom
The reinforcement
in
in
satisfied the
be reinforced
mm. The
total
two directions.
the direction of the length of the pier shall extend from end to end
50
IRC:78-2014 of the pier piers
one
cap while the reinforcement
cap and be 20
at
mm
in
the form of stirrups.
from top and the other
consisting of 8
mm
bars at 100
mm
angles shall extend for the
at right In
addition,
100
at
centres
mm
full
width of the
two layers of mesh reinforcement
from top of pedestal or pier cap each
both directions shall be provided directly
in
under the bearings.
71 0.9
Cantilever
710.9.1
When
support
is
Cap
of Abutment
and
Pier
the distance between the load/centre line of bearing from the face of the
equal to or less than the depth of the cap (measured at the support) the cap shall
be designed as a corbel.
The equivalent square area may be worked out
710.9.2
the face of support for calculating bending
710.9.3
In
measurement
case of wall of distance for
of reinforcement should
be
nearest supporting face of
Where a
710.9.4
pier
in
determine
moments.
and the
pier
cap cantilevering out
all
around, the
purpose of the design as bracket and the direction of provision parallel to the line joining the centre of load/bearing with the
Pier.
part of the bearing lies directly over the pier, calculation of such
reinforcement should be restricted only for the portion which
Moreover,
for circular pier to
such cases the area of closed horizontal
is
stirrups
outside the face of the
may be
limited to
pier.
25 percent
of the area of primary reinforcement.
710.10
Pedestals below Bearing
710.10.1
The pedestals should be so proportioned
the edges of bearings
710.10.2
is
The height
that a clear offset of
of the pedestal should
require use of pedestals of
diaphragm
50
mm beyond
available.
be between 150
the depths of superstructures from two adjacent spans on a
or the
1
more height below one
of superstructure shall
500 mm. For pedestals whose height is
be modified
less than
its
mm
and 500 mm. Where
common
of the spans, the
pier differ
shape
of pier
and cap
to restrict the height of pedestals to
width, the requirement of the longitudinal
reinforcement as specified for short column need not be insisted upon.
710.10.3
The allowable bearing pressure
with near uniform distribution on the loaded
51
IRC:78-2014 area of a footing or base under a bearing or coiumn shall be given by the following equation.
C
=
/
A
.
_
i
C xv A 0
C
>
0
where
Co
=
the permissible direct compressive stress
in
concrete at the
bearing area of the base
A
=
dispersed concentric area which
is
geometrically similar to the
1
A 2 and also the largest area that can be contained in of A (maximum width of dispersion beyond the loaded
loaded area the plane
1
area face shall be limited to twice the height)
A2
-
loaded area and the projection of the bases or footing beyond the face of the bearing or column supported on
150 710.10.4 at
100
The two
mm
layers of
mm from top of pedestal
directions, shall
be provided
in
any
directly
shall not
be less than
direction.
mesh reinforcement or pier
it
-
one
at
20
cap each consisting of 8
under the bearings. *****
52
mm from top and the other mm bars at 100 mm in both
IRC:78-2014
Appendix-1 (Clause 703.2.2.2)
GUIDELINES FOR CALCULATING SILT FACTOR FOR BED MATERIAL CONSISTING OF CLAY any formula 'KJ may be determined as per Clause 703.2.2 and may be adopted based on site information and behaviour history of any existing structure. The In
absence
of
clayey bed having weighted diameter normally less than
scour than sand though indicates
more
scour. In
mean depth absence
rational formula or
the site of the proposed bridge; the following theoretical calculation
i)
In
case of
having
soil
offers
of scour as per the formula given
any accepted
of
0.04mm
0
more resistance in
Clause 703.2
any data of scour
at
may be adopted:
0.2
soil)
kg/cm 2
'KsfI calculated as follows:
K
=
sf
F(1 +
Vcj
where c
in
kg/cm 2
where
F
ii)
= 1.50 for
0>
= 1.75 for
0>5°
= 2.00
0<
for
10° and < 15°
and < 10°
5°
Soils having 0 >15°
2N/mm and 2
silt
will
factor
will
be treated as sandy
soil
even
if
c
is
more than
be as per provisions of Clause 703.2.2.
53
!RC:78-2014
Appendix-2 (Clause 704.3)
GUIDELINES FOR SUB-SURFACE EXPLORATION
GENERAL
1
The
objective of sub-surface exploration
for the foundation of bridges.
is
determine the
to
The sub-surface
stages, namely preliminary and detailed.
It
exploration for bridges
may
the
suitability of is
soil
or rock,
carried out
in
two
require additional/confirmatory exploration
during construction stage.
Guidance may be taken from the IS
i)
1892
-
Code
of Practice for Site Investigation for Foundations
Test on soils shall be conducted
2720
-
may be
guidance regarding investigation and collection of data.
utilised for
ii)
following:
Methods
conducted as
far
in
of Test for Soils.
accordance with relevant part of
The
tests
as possible at simulated
IS
on undisturbed samples be
field
conditions to get realistic
values. iii)
IS 1498-Classification
and
Identification of Soils for general engineering
purposes. For preliminary and detailed sub-surface investigation, only rotary
drills shall
casing shall also be, invariably provided with diameters not less than 150 rock,
if
any. However, use of percussion or
wash
mm
be used. The
upto the level of
boring equipment shall be permitted only to
penetrate through bouldery or gravelly strata for progressing the boring but not for collection of samples. While conducting detailed borings, the resistance to the rate of penetration, core loss, etc. shall
and data sheet"
be carefully recorded and presented
to evaluate the different
sandstone, clay from shale,
speed in
of drilling,
"Borelog chart
types of strata and distinguish specially sand from
etc.
For preliminary and detailed sub-surface investigation, only double tube diamond
method
shall
drilling shall
be used.
In soft
information,
and weak rocks such
tuffs, soft
shales
etc., triple
drilling
tube diamond
be used.
2 2.1
i.e.,
Preliminary
previous
PRELIMINARY INVESTIGATION
investigation site
reports,
shall
include
geological
54
the
maps,
of
existing
geological
and
surface
geological
study etc.,
IRC:78-2014 examination. These
and also
to locate the
most desirable
number
the
of sites under consideration
location for detailed sub-surface investigation.
DETAILED INVESTIGATION
3
Based on data obtained
3=1
down
help to narrow
will
after preliminary investigations,
the type of structure with span arrangement and the location the
programme
the bridge
and type
site,
of foundations,
of detailed investigations, etc. shall be tentatively decided. Thereafter
the scope of detailed investigation including the extent of exploration, holes, type of tests,
number
of tests, etc. shall
be decided
in
number
of bore
close liaison with the design
engineer and the exploration team, so that adequate data considered necessary detailed design
end a distance last
and execution are obtained.
The
3.2
for
exploration shall cover the entire length of the bridge and also at either of
zone
main foundation
to
of influence,
assess the
i.e.,
about twice the depth below bed of the
approach embankment on the end
effect of the
foundations. Generally, the sub-surface investigations should extend to a depth below the anticipated foundation level equal to about
where such
foundation. However,
one and a
investigations
end
in
half times the width of the
any unsuitable or questionable
foundation material, the exploration shall be extended to a sufficient depth into firm
and stable
soils or to rock.
Additional
3.2.1
drill
holes:
Where
indicate appreciable variation specially
necessary strata.
to resort to additional
in
local
in
The scope
made
available by detailed exploration
case of foundations resting on
in
rock,
it
will
be
holes to establish a complete profile of the underlying
Location and depth of additional
the extent of variation
3.3
drill
the data
holes
drill
geology and
in
will
have
to
be decided depending upon
consultation with design engineer.
of the detailed sub-surface exploration shall
para 3.1 and 3.2. However, as a general guide
it
shall
be fixed as mentioned
be comprehensive enough
to
enable the designer to estimate or determine the following:
i)
engineering properties of the soil/rock;
ii)
location
and extent of weak layers and
cavities,
if
any,
below hard founding
strata; iii)
the sub-surface geological condition, such as, type of rock, structure of rock,
i.e.,
folds, faults, fissures, shears, fractures, joints,
subsidence due
to mining or
55
presence of
cavities;
dykes and
IRC:78-2014 iv)
ground water
v)
artesian conditions,
level;
water
if
any;
contact with the foundation;
vi)
quality of
vii)
depth and extent of scour;
viii)
suitable foundation level;
ix)
safe bearing capacity of foundation stratum;
x)
probable settlement and probable
xi)
likely
sinking or driving effort;
xii)
likely
construction
in
differential
settlement of the foundations;
and
difficulties.
CONSTRUCTION STAGE EXPLORATION
4
Such exploration may become necessary investigation stage or
when a change
during construction.
such
In
situations,
to verify the actually
in it
met
strata vis-a-vis detailed
the sub-soil strata/rock profile
may be
is
encountered
essential to resort to further explorations
to establish the correct data, for further decisions.
5 The
METHOD OF TAKING SOIL SAMPLES
size of the bores shall be predetermined so that undisturbed
various types of tests are obtained.
and
IS 2132.
The
6
on
samples
soil
groups keeping
method
of taking
samples
shall
be as given
in
for the
IS1892
be conducted as per relevant part of IS 2720.
shall
DETAILS OF EXPLORATION FOR FOUNDATIONS RESTING ON SOIL (ERODIBLE STRATA)
The type and extent
6.1
in
of
exploration
shall
be divided
into
the
following
view the different requirements of foundation design and the
likely
of data collection:
i)
Foundations requiring shallow depth of exploration;
ii)
Foundations requiring large depth of exploration; and
iii)
Fills
behind abutments and protective works.
Foundations Requiring Shallow Depth of Exploration (Open Foundation)
6.2
These
tests
The method
samples as required
shall
cover cases where the depth of exploration
samples from shallow
pits or
conduct direct
cover generally the foundation
soil for
is
not large
and
it
is
possible to take
tests, like, plate load tests, etc. This will also
approach embankments, protective works,
56
etc.
IRC:78-2014
The primary requirements are
6.2.1
stability
and settlement,
which shearing
for
strength characteristics, load settlement characteristics, etc. need determination.
Tests shall
6.2.2
may be
be conducted on undisturbed representative samples, which
obtained from open
Test on Soils)
of plate load test (IS
1
888-Method
A
few exploratory bore holes or soundings
shall
made
be
safeguard against presence of weak strata underlying the foundation. This shall extend
to a
depth of about
NOTE:
1
V 2 times the proposed width of foundation.
For better interpretation, in-situ tests, like, plate
The
6.2.3
cohesionless
tests to be
soils.
it
will
to correlate the laboratory results with the
load tests, penetration test results.
conducted
These are
be desirable
for properties of soil are different for
indicated below. While selecting the tests
cohesive and
and
interpreting
the results, limitations of applicability of chosen tests shall be taken into account. suitable
and appropriate combination of these
needed
for
I)
most
be chosen, depending on the properties
Cohesionless Soil Laboratory Tests Classification tests, index tests, density determination, etc.
i)
ii)
b)
NOTE:
shall
A
design and constructional aspects.
a)
Shear Strengths by
Load
Test, (as per IS 1888).
i)
Plate
ii)
Standard Penetration Tests (as per IS 2131)
iii)
Dynamic Cone Pentration
iv)
Static
Where
Cone
2720 Part
Test, (as per IS
Penetration Test, (as per IS
dewatering
Cohesive a)
triaxial/direct shear, .etc.
Field Tests
(as per IS II)
Load
of
considered desirable for ascertaining the safe bearing pressure and
is
settlement characteristics. to
The use
pits.
is
expected,
permeability
4968 Part or Part I
4968 Part tests
III).
may
be
XVII).
Soil
Laboratory Tests i)
Classification tests, index tests, density determination etc.
ii)
Shear strengths by
iii)
Unconfined compression test
iv)
Consolidation test (IS 2720 Part V)
triaxial/direct shear, etc.
57
(IS
2720 Part X)
II).
conducted
IRC:78-2014 b)
Field Tests
Load
Test, (as per IS: 1888).
i)
Plate
ii)
Vane Shear
iii)
Static
iv)
Standard Penetration Test, (as per IS:21 31
v)
Dynamic Cone Penetration
Cone
Where dewatering
NOTE:
Test, (as per IS:4434).
Penetration Test, (as per IS:4968 Part
Test, (as per IS:4968 Part
expected,
is
III).
permeability
tests
I
or Part
II).
may be conducted
(as per IS:2720 Part XVII). S
Foundations Requiring Large Depth of Exploration
3
6.3.1 In this
group are covered cases of deep wells,
pile
foundations,
boring equipment, special techniques of sampling, in-situ testing, etc. addition to the problems of soil
the
soil
soils,
and foundation
interaction
where the use
etc.,
become
of
essential. In
an important consideration can be
data required from construction considerations. Often
in
the case of cohesionless
made
undisturbed samples cannot be taken and recourse has to be
to in-situ
field tests.
Boring and sampling tends to cause remoulding of sensitive clays. Also for fissured
sample may not truly represent the in-situ properties, due to disturbance and stress changes caused by boring and sampling activity. In such cases,
or layered clays, the
in-situ tests shall
be performed.
The sub-surface
6.3.2
exploration can be divided into three zones:
between bed
i)
level
and upto anticipated maximum scour depth (below
H.F.L.)
maximum scour depth
ii)
from the
iii)
from foundation
Sampling and testing
6.3.3
case and hence are required soil
level to
water
shall
to foundations.
be tested
for
to
to the foundation level,
and
about 1V2 times the width of foundation below
(in-situ
and laboratory) requirement
will
vary
in
it.
each
be assessed and decided from case-to-case. The sub-
chemical properties to evaluate the hazard of deterioration
Where dewatering
is
expected
to
be required, permeability characteristics
should be determined. For the different zones categorised
6.3.4
sampling, testing, etc. are given at
every
1
to
1
V 2 metre or
at
in
change
Table
in
para 6.3.2., the data required, method of
Samples
1.
of strata.
58
of soils
in all
cases
shall
be collected
IRC:78-2014
Table Zones Bed
1
Sub-Soil Data Required for Deep Foundations Data/Characteristics Required
level to anticipated
Soil Classification
Sampling
ii)
Particles size distribution
Disturbed samples
iii)
Permeability,
i)
maximum scour depth
Sampling and Testing
dewatering
may be Laboratory Tests -
where
collected.
Classification Tests, including particle size distribution.
expected.
is
-
In-situ Tests :Permeability tests.
Maximum
anticipated
Sampling
for Laboratory Tests Undisturbed samples shall be collected for these tests. As an exception, for (i) and (ii), disturbed samples may
Soil Classification.
i)
scour level to the
ii)
Particles size distribution
foundation level
iii)
Moisture content, density,
be permitted.
void ratio.
Shear
iv)
Laboratory Tests
-
strength. a) Classification Tests including particle size
v) Compressibility.
distribution.
Permeability where
vi)
dewatering vii)
is
expected.
Chemical analysis of ground water elements
b) Moisture content, density, void ratio
(for
soil
c)
Shear strength
-
Triaxial tests to
be done on
undisturbed samples. Unconfined
and
compression tests
aggressive
to
be done on undisturbed
and/or remoulded samples ).
d) Consolidation tests.
Tests for Cohesioniess soilsDynamic Cone Penetration Test.
In-situ a) b)
Standard Penetration Test.
c)
Down
hole/Cross hole seismic surveys.
d) Permeability tests.
In-situ Tests for
Cohesive Soils
a)
Dynamic Cone Penetration
b)
Static
Cone
-
Test.
Penetration Test
-
cone and skin
resistance
Foundation 1
.5
level to
about
times of the width of
foundation and below
it.
i)
iii)
Field
Permeability tests.
e)
Down
Same
Soil Classification
ii)
Vane Shear
c)
d)
Test.
hole/Cross hole seismic surveys.
as above
Shear Strength Compressibility
Notes: 1
)
2)
Laboratory tests to be conducted according to the relevant parts of IS 2720,
Use
of sophisticated
equipment
like,
pressure meter
may be made,
if
suitable co-relations for interpretation of data collected are
available.
ASTM
3)
Down
4)
Seismic Methods and/or Electrical Resistivity Method can be used
hole/Cross hole seismic surveys shall be as per
4428/D 4428
M
for soil/rock profiling.
Down
hole/Cross hole seismic surveys
could be used for establishing elastic moduli and rock profiling at greater depths. 5)
Down
hole/Cross hole seismic surveys are useful
of bores taken
methods
shall
in
for long
bridges
(i.e.
of the order of
1
km and above) and
for
reducing the number
the portions that are permanently under water. For these applications, geotechnical profiles obtained by seismic
be calibrated/confirmed with actual
profiles
taken by bores at intermediate locations.
59
IRC:78-2014 6.4
Materials
Fill
Representative disturbed samples shall be collected from the borrowpit areas. Laboratory tests shall
be conducted
and
particle size
)
classification
i)
moisture content
ii)
density vs. moisture content relationship
v)
shearing strength permeability
v)
NOTE:
determining the following:
for
The shearing
strength shall be obtained for the density corresponding to the
proposed density
7
for the
fill.
DETAILS OF EXPLORATION FOR FOUNDATION
RESTING ON ROCK Basic Information Required from Explorations
7.1
Geological system;
ii)
Depth of rock and
iii)
Whether
iv)
Extent and character of weathered zone;
v)
The
vi)
Properties of rock material,
vii)
Quality
viii)
Erodibility of rock to the extent possible,
variation over the site;
its
massive rock formation;
isolated boulder or
structure of rock-including bedding planes, faults, etc.;
and quantity
Exploration
7.2 If
i)
like,
of returning
strength, geological formation, etc.; drill
water; and
where relevant
Programme
preliminary investigations have revealed presence of rock within levels
foundation
is
to rest,
it
is
information mentioned
7.2.1
essential to take up detailed investigation to collect necessary
in
The extent
the preceding para.
of exploration shall
picture of the rock profile, both
constructional difficulties
where the
in
in
be adequate enough
to give a
complete
depth and across the channel width, for assessing the
reaching the foundation levels. Keeping this
in
view,
it
shall
be
possible to decide the type of foundations, the construction method to be adopted for a particular bridge, the extent of It
is
desirable to take atleast
even seating and embedment
one
drill
into rock of the foundations.
hole per pier and abutment and one on each side
beyond abutments.
60
IRC:78-2014
The depth
7.2.2
of boring
in
rock depends primarily on local geology, erodibility of
the rock, the extent of structural loads to be transferred to foundation, etc. Normally,
pass through the upper weathered or otherwise weak zone, well
minimum depth
case of rock
at shallow
rock.
shall
The
be as per para 3.2 above.
Detailed Investigations for
7.3
In
of drilling shall
sound
into the
it
Rock
at
Surface or at Shallow Depths
depths which can be conveniently reached, test
pits or
trenches are the most dependable and valuable methods, since they permit a direct
examination of the surface, the weathered zone and presence of any discontinuities. For guidance, IS 4453
may be
referred
to. In
accordance with flat
IS
-
Code
of Practive for exploration by pits, trenches, drafts
case of
structurally disturbed rocks, in-situ tests
7292 - Code
and shafts
may be made
in
of Practice for in-situ determination of rock properties by
7317 - Code of Practice for Uni-axial Jacking Test for Deformation Modulus 7746 - Code of Practice for in-situ Shear Test on Rock.
jack, IS
and
IS
Rock
7.4
Detailed Investigation for
7.4.1
This covers cases where recourse
drilling.
An adequate
investigation
to
is
of exploration will
be
made
at the preliminary investigation
The
7.4.2
and
its
tests
on overburden
shall
in soil.
cover the whole
to
variation over the foundation area.
depend on the type and depth
may be
stage
However,
in
The
of overburden,
geophysical methods
this,
helpful.
investigation of the overburden soil layers shall
given for the foundations resting
sounding, boring and
be planned
to
the size and importance of the structure, etc. To decide
adopted
to
particular the foundation location, for obtaining
in
definite information regarding rock-depth
programme
Large Depths
programme has
area for general characteristics and
detailed
at
be done as per
details
case of foundations resting on rock,
be carried out only when necessary,
e.g.,
foundation level lower
than scour levels.
7.4.3 for Indexing
The core
and Storage
most transparent
7.4.4
shall
be stored properly of
Drill
in
Cores. Wherever
plastic tube shall
be stored
The rock cores obtained
shall
be subjected
Visual identification for a)
triple
Texture
61
-
Code
tube core barrel
directly in core
design as follows:
i)
accordance with IS:4078
in
of Practice
used, inner
box with sample.
to tests to get
necessary data
for
IRC:78-2014 Structure
c)
Composition
d)
Colour
e)
Grain size
f)
Petrography
Laboratory tests
ii)
NOTE:
b)
may be done
a)
Specific gravity
b)
Porosity
c)
Water absorption
d)
Compressive strength
Generally, shear strength tests to
be done
special case.
in
compression,
Use
7.4.5
triaxial
suffice for design purposes.
The shear
compression or
of bore hole photography
will
faults, fissures or cavities, etc. Particularly in
tube core barrel
triple
is
used
strength tests can be direct
shear
Other tests
may need
done as unconfined
test.
measuring strength and deformation characteristics
of in-situ tests for
may be made. Use
will
for
be desirable
weak and/or
to evaluate the
highly
weathered
presence of rock,
where
such as Standard Penetration Test
for drilling, in-situ tests
and/or pressure meter test shall be conducted at every
1
.5
m
interval in the influence
zone
of footing or pile.
These
in-situ tests
However drilling
A
in
zones where water loss
selections of these tests have to be
done
is
judiciously
recorded during
drilling.
and planned along with
operation.
Special Cases
7.5 7.5.
are also useful
investigation for conglomerate
1
drill
hole shall be
suitable tests
made same as
for rock.
The samples
depending upon the material. Special care
collected shall be subjected to shall
be taken
to ascertain the
credibility of the matrix.
7.5.2
The hard
investigation for iaterites
investigation shall generally be similar to that required for cohesive soils. In iaterite,
recourse
may have
to
be
made
to
62
core
drilling
as for soft rocks.
case of
IRC:78-2014
CLASSIFICATION AND CHARACTERISTICS OF ROCKS
8
Identification
8.1 in
and
classification of rock types for engineering
general, be limited to broad, basic physical condition
practice. Strength of parent rock alone
depend considerably on
is
of limited value
character, spacing
and
in
purposes may,
accordance with accepted
because
overall characteristics
distributions of discontinuities of the
rock mass, such as, the joints, bedding, faults and weathered seams. 8.2
Classification of
Rocks may be
classified
Rocks
based on
their physical condition
and Unconfined Compressive
Strength as per Table-2.
9
Presentation of Data
The Presentation
be as done as
of Data collected shall
Table
-
Rock Type
illustrated in
Sheet No
1
and 2
2 Classification of Rocks
Unconfined
Description
Compressive Strength (UCS) in
Extremely
Cannot be scratched with
Strong
specimen could be done by sledge hammer
Very Strong
Cannot be scratched with of
knife or
sharp
knife or
pick.
sharp
Breaking of >200
only.
pick.
specimens requires several hard blows
MPa
Breaking
100
to
200
of geologists'
pick.
Strong
Can be scratched with knife or pick with difficulty. Hard 50 blow of hammer required to detach hand specimen.
Moderately
Can be scratched
with knife or pick, 6
Strong
or grooves can be
made
mm
deep gouges 12.5
by hand blow of geologists'
Hand specimen can be detached by moderate
mm deep
or
Weak
on
Can be broken into pieces or chips maximum size by hard blows of the points
.5
knife or pick point.
of about 2.5
mm
of geologists' pick.
63
to
50
blow.
Can be grooved
1
100
pick.
Moderately
gouged
to
by firm pressure 5 to 12.5
IRC:78-2014
Weak
Can be grooved or gouged easily with knife or pick point. Can be break down in chips to pieces several em's in size by moderate blows of pick
point.
1
.25 to 5
Small thin pieces can be
broken by finger pressure. Very weak
Can be carved
with knife.
of pick. Pieces
25
Can be broken
easily with point
mm or more in thickness can
< 1.25
be broken
by finger pressure. Can be scratched easily by finger
nail
Note: 1)
The Unconfined Compressive Strength values are as
2)
Table-2 should not be used to infer the Unconfined Compressive Strength of rock. Actual laboratory test value of rock core should be used.
64
in British
Standard BS-5930
(CI. 44.2.6).
^
-
IRC:78-2014
RL.
(NOTE:
OF GROUND BORE 75.00 (REF. LEVEL)
SHEET No.!
FEU) TKT RESULTS
U)
D-
3
a.
n
4^
STATIC PENETRATION
RESISTANCE kg/cm
30cm
u £
2
"Bt °Ss
z
i-
o M u. LJ o
VISUAL DESCRIPTION
-J
0«"
K El
I
SKIN
POINT Q.
RESISTANCE RESISTANCE
St
huvvnor«MOMmp»«only
n
vHuW
IRC:78-2014
Appendix-3 (Clauses 708.2, 708.3 and 708.4)
PROCEDURE FOR 1
The
active
FORMULA FOR ACTIVE OR PASSIVE PRESSURE
and passive pressure
co-efficient
according to Coulomb's formula taking 'c'
Kp
(Ka &
IN
SOIL
respectively) shall be calculated
account the wall
into
may be added to the same as rd friction may be taken as 2/3 of 0
effect of
of wall
STABILITY CALCULATION
friction.
per procedure given by the angle of repose
is
For cohesive
Bell.
soils,
The value
subject to a
degrees. Both the vertical and horizontal components shall be considered
limit
in
the
of angle
of
22
2
the stability
calculations.
2 SKIN The
relief
due
to skin friction shall
in-charge. However,
FRICTION
be ignored unless
case of highly compressive
in
specifically permitted soils, skin friction,
by the Engineer-
if
any,
may cause
increased bearing pressure on the foundation and shall be dully considered.
3 The
FACTOR OF SAFETY OVER ULTIMATE PRESSURES
factor of safety
in
assessing the allowable passive resistance shall be 2
combinations without wind or seismic forces and 1.6
for load
for load
combinations with wind or
seismic forces. The manner of applying factor of safety shall be as indicated below: i)
Pier wells founded
The
factor of safety
the net ultimate
soil
in
cohesive
soils
as stipulated resistance,
viz.,
(P
passive and active pressure respectively
scour ii)
-
for
Pg where Pp and Pa are total mobilised beJow the maximum )
level.
Abutment wells In
be applied
for the type of soil shall
in
both cohesive and non-cohesive soils
the case of abutment wells, the active pressure on
maximum scour
soil
level (triangular variation of pressure) shall
above the
be separately
evaluated and considered as load combined with the other loads acting
on the abutment and no factor of safety shall be taken for the above components of active pressure. Effects of surcharge due to live load should be restricted only upto the abutment portion. 67
IRC:78-2014 iii)
However, the
laterai resistance of soil
below the scour
value shall be divided by the appropriate factor of safety, stated iv)
in
level at ultimate viz.,
the case of pier wells.
(p
_
pj
as
~FOS
Point of rotation
For the purpose of applying the above formulae, the point of rotation
lies at
it
may be assumed
the bottom of the well.
INNER DREDGE HOLE
OUTER SURFACE
rr
Kd
h
m
Kd1
hi
WHERE
m OUTER
d1
DIA
OF WELL
AFTER REDUCTION IN STONING THICKNESS
IS
Id
* DEPTH OF WELL UPTO MSL ^ 3 (h-h1)
k
WE
THE DEVELOPMENT LENGTHS FOR THE STEEL. BEYOND THE MINIMUM SECTION tl
Fig.
1
Sketch
for
t
t2
Reduction of Steining Thickness
68
that
IRC:78-2014
L
69
«sr
IRC:78-2014
IRC:78-2014
Appendix-4 (Clause 708.13)
PRECAUTIONS TO BE TAKEN DURING SINKING OF WELLS 1
CONSTRUCTION OF WELL CURB AND STEINSNG
Cutting
1 .1
1.2
conditions,
edge and the top
the curb atleast partially for
The
1.4
always be
built in
lifts
and the
in
one
In
soft strata
shall
lift
depend on the
be
laid after
site
sinking
the well
prone
bottom to top and
straight line from
at right angle to the plane of the curb. In
when
first
shall
truly horizontal.
stability.
steining shall be built
intermediate stages
1.5
be placed
The methods adopted for placing of the well curb and the cutting edge shall be placed on dry bed. Well steining shall be
1.3
of the well curb shall
no case,
shall
it
be
shall
plumb
built
in
is tilted.
abutment
to settlement/creep, the construction of the
wells shall be taken up after the approach
embankment
for a sufficient distance
near
the abutment has been completed.
2 2.1
A sinking
2.2
Efforts shall
2.3
Sumps made
history record
be made
SINKING
be maintained
at site.
to sink wells true to position
by dredging below cutting edge
and
in
plumb.
shall preferably not
be more
than half the internal diameter. 2.4
Boring chart shall be referred to constantly during sinking for taking adequate
care while piercing different types of strata by keeping the boring chart at the plotting the soil
to take
as obtained
for the well steining
and comparing
it
site
and
with earlier bore data
prompt decisions.
When the wells have to
each other and the clear distance is less than the diameter of the wells, they shall normally be sunk in such a manner that the difference in the levels of the sump and the cutting edge in the two wells do not exceed half the clear gap between them. 2.5
be sunk close
71
to
IRC:78-2014
When
2.6
they do not sunk.
fail in
group of wells are near each
The minimum clearance between in
level
needed
to
ensure that
the wells shall be half the external diameter.
dredging shall be carried out
the group and plugging of
During construction
2.7
is
the course of sinking and also do not cause disturbance to wells already
Simultaneous and wells
other, special care
all
the wells be
partially
done
sunk wells
in
the dredging holes of
the
all
together.
shall
be taken
to
a safe depth below
the anticipated scour levels to ensure their safety during ensuing floods.
Dredged material
2.8
shall not
Where
such load
shall
the middle to
is
loaded with Kentledge
remove excavated
of the load shall
to provide additional sinking effort,
be placed evenly on the loading platform, leaving
Where
3.2
a well
be regulated
sufficient
space
in
material.
are present or there
tilts
well.
USE OF KENTLEDGE
3 3.1
be deposited unevenly around the
in
is
a danger of well developing
such a manner as
tilt,
the position
to provide greater sinking effort
on
the higher side of the well.
SAND BLOWS
4 Dewatering
4.1
be avoided
shall
and men working inside the
well shall
IN
WELLS
sand blows are expected. Any equipment
if
be brought out of the well as soon as there are
any indications of a sand-blow.
Sand blowing
4.2
in
wells can often be minimized by keeping the level of water
inside the well higher than the water table
5 SINKING Use
5.1
of divers
OF WELLS WITH USE OF DIVERS
may be made
removal of obstructions, rock blasting, shall
shall
in
etc.
well sinking both for sinking purposes,
as also
be taken as per any acceptable safety code
regulations
5.2
and also by adding heavy kentledge.
in
like,
for inspection. All safety precautions
for sinking with divers or
any statutory
force.
Only persons trained
for the
diving
operation shall be employed.
work under expert supervision. The diving and other equipments
acceptable standard.
It
shall
be well maintained
72
for safe use.
shall
They
be of an
IRC:78-2014 Arrangement
5.3
ample supply
for
ensured through an armored to
be provided
hose
flexible
of low pressure
made.
be
shall
air
Standby compressor plant
pipe.
will
have
case of breakdown.
in
Separate high pressure connection
5.4
clean cool
Electric lights,
where provided,
be
shall
use of pneumatic tools
for
at
50
volts
(maximum). The
be
shall
raising of
the diver from the bottom of wells shall be controlled so that the decompression rate
conforms
for divers
5.5
All
to the appropriate rate
men employed
for diving
as
laid
down
purpose
in
shall
the regulation.
be
be
certified to
fit
by
for diving
an approved doctor.
6 Only
6.1
be
fired
light
charges
shall
BLASTING
be used under ordinary circumstances and should
under water well below the cutting edge so that there
is
no chance of the curb
being damaged.
There
6.2
shall
be no equipment inside the well nor
shall there
by any labour
in
the close vicinity of the well at the time of exploding the charges.
6.3
All
Blasting is
safety precautions shall
and Related
resorted
to.
Use
be taken as per
4081
IS
"Safety
whenever
Operations", to the extent applicable,
Drilling
of large charges,
may
0.7 kg. or above,
Code
for
blasting
not be allowed except
under expert direction and with permission from Engineer-in-charge. Suitable pattern of charges fired at
holes
may be arranged
with delay detonators to reduce the
may be
a time. The burden of the charge
may
6.4
limited to
1
m
number
of charges
and the spacing of
normally be kept 0.5 to 0.6 m.
If
rock blasting
is
to
be done
for seating of the well, the
damage caused by
the flying debris should be minimised by provisions of rubber mats covered over the blasting holes before blasting.
6.5
measures
After blasting, the steining shall be *shall
for
any cracks and corrective
be taken immediately.
7 7.1
examined
The pneumatic
of proper design
PNEUMATIC SINKING
sinking plant
and make, but also
and other
shall
personnel. Every part of the machinery and
allied
machinery
shall not only
be
be worked by competent and well trained
its
73
fixtures shall
be minutely examined before
IRC:78-2014 installation
and use. Appropriate spares, standbys, safety
4188
working
compressed
must be kept
in
the IS
in
and other labour laws and practices prevalent
efficient
for
in
and expeditious sinking
air
at site. Safety
code
working
for
the country, as specified to provide safe,
in
be followed.
shall
Inflammable materials shall not be taken
7.2
recommended
of personnel as
into air locks
and smoking
shall
be
prohibited.
Whenever gases
7.3 shall
be analysed by trained personnel and necessary precautions adopted
hazard
to
life
avoid
to
and equipment.
Where
7.4
same
are suspected to be oozing out of dredge hole, the
blasting
resorted
is
to,
shall
it
be carefully controlled and
ail
precautions
regarding blasting shall be observed. Workers shall be allowed inside after blasting only
a competent and qualified person has examined the
The weight
7.5 shall
be
of
chamber and
steining thoroughly.
pneumatic platform and that of steining and kentledge,
sufficient to resist the uplift
from
when
air inside, skin friction
being neglected
if
any,
in this
case. 7.6
If
pressure of
7.7
at
any section the
air inside, additional
If it
is
total
weight acting downwards
is
less than the uplift
kentledge shall be placed on the well.
make the well heavy enough during excavation; The men should be withdrawn and the air pressure begin to move with a small reduction in air pressure.
possible to
Down" may be used. The well should then
Down" should only be used where the ground is such that will not heave up chamber when the pressure is reduced. When the well does not move with a it
in
air
pressure, kentledge should be added. Blowing
and the drop should not exceed, 0.5
m
of
down should be
any stage. To
in
"Blowing reduced. "Blowing inside the
reduction
short stages
control sinking during blowing
down, use of packs or packagings may be made.
8 TILTS 8.1
Tilts
and
shifts
shall
AND SHIFTS OF WELLS be carefully checked and recorded regularly during
sinking operations. For the purpose of measuring the
tilts
along and perpendicular to
the axis of the bridge, level marks at regular intervals shall be painted on the surface of the steining of the well.
8.2
Whenever any
tilt
is
noticed,
adequate preventive measures,
like,
putting
eccentric Kentledge, pulling, strutting, anchoring or dredging unevenly and depositing
74
IRC:78-2014 dredge material unequally, putting obstacles below cutting edge,
after jetting etc., shall
be adopted before any further sinking. After correction, the dredged material placed unevenly shall be spread evenly.
A
8.3 sinking.
prevent
pair of wells close to
Timber
struts
may be
each other have a tendency
introduced
in
to
between the steining
come
closer while
of these wells to
tilting.
8.4
Tilts
occurring
in
a well during sinking
in
dipping
rocky strata can
be
safeguarded by suitably supporting the kerb.
9
Sand
9.1
be
level
shall
wave
action.
9.2
dimension
island
where provided
sufficiently
above the
The dimension in
SAND ISLAND
of the
shall
be protected against scour and the top
prevailing water level so that
sand island
plan of the well or caisson.
75
shall
it
is
safe against
not be less then three times the
IRC:78-2014
Appendix-5 (Clause 709.3.1)
CAPACITY OF PILE BASED ON PILE SOSL INTERACTION 1
AXIAL CAPACITY OF PILES
Axial load carrying capacity of the pile
end bearing soil
is initially
Qu
Ru +R
=
SOIL
determined by calculating resistance from along
at toe/tip or wall friction/skin friction
data, the ultimate load carrying capacity
IN
(QJ
is
pile
surface or both. Based on the
given by:
f
f
where
R R
= Ultimate base resistance
= Ultimate shaft resistance f
Ru
=
Ru,
i.e.,
may be calculating from the following: A P Nc CP
Ultimate base resistance
Ru =AP (V2
DYNy + PdNq
)
+
where
A
= Cross-sectional area of base of
D
- Pile diameter
Y
= Effective unit weight of
N & Ny N
= Bearing capacity factors based on angle of internal
- Bearing capacity factor usually taken as 9
C
= Average cohesion at
Pd
-
c
Effective pile
R
i.e.,
in
pile
cm soil at pile tip in
kg/cm 3 friction at pile tip
(from unconsolidated untrained test)
pile tip
overburden pressure at pile tip limited to 20 times diameter of
for piles
having length equal to more than 20 times diameter
Ultimate side resistance
may be
calculated from the following:
f
R=t KP tanSA dj
si
+
ocCA
s
where
K
= Coefficient of earth pressure
P
= Effective overburden pressure
dj
pile for
5
the layer
- Angle of wall
ith
friction
= Surface area of
/'
between
pile shaft in
pile
= Surface area of
cm 2
pile shaft in
76
and
/
to
soil in
n degrees.
It
may be taken
friction of soil in
the
sj
As
kg/cm 2 along the embedment of
where varies from
equal to angle of internal
A
in
cm 2
ith
layer,
where varies from /'
7
to
n
IRC:78-2014
a
- Reduction factor
c
= Average cohesion
in
kg/cm 2 throughout the embedded length of pile
(from unconsolidated untrained test)
While evaluating effective overburden pressure,
3 of soil shall
up
to
1
The
value of
initial
.8 in particular
5
and submerged weight
be considered above and below water table respectively.
The
4
total
K may
be taken as 1.5 which can be further increased
cases as specified
following value of x
in
(v).
may be adopted depending upon
N Value Bored
Consistency
Clause 709.2.2
consistency of
Driven
piies
Cast-in-situ
case-in-situ piles
Soft to very soft clay
15
0.30
0.3
Very
stiff
6
For piles
7
When
in
full
over consolidated
static penetration
A +f .A Q u =q"bp h
qb =
s
soils,
data
is
f
=
may be
evaluated.
available for the entire depth, then
Point resistance at base to be taken as average of the value over a depth
below the =
the drained capacity
s
equal to 3 times the diameter of
A
soil:
above and one time the diameter of
pile
pile
tip.
Cross-sectional area of base of pile
Average side
friction
Type of Soil
and following Side
co-relation
may be used as
a guide:
Friction, f s
Clay Soft
q c/25
Stiff
q)l5
Mixture of
qc 8
silts
and sand with traces
Loose
q c/50
Dense
q c/100
of clay
Static point resistance.
Where
soft
compressible clay layer
capacity of pile from such
downward drag on
pile
due
soil
shall
is
encountered, any contribution towards
be ignored and additional load
to consolidation of soft soil shall
77
pile
be considered.
on account of
IRC:78-2014
NOTE:
For factors of safety of piles
CAPACITY OF PILES
9
Axial
9.1
Piles
IN
in soil,
Clause 709.3.2.
refer
INTERMEDIATE GEO-MATERIAL AND ROCK
Load Carrying Capacity
:
rocks and weathered rocks of varying degree of weathering derive their capacity
in
by end bearing and socket side resistance. The ultimate load carrying capacity
may
be calculated from one of the two approaches given below:
Where cores
can be taken and unconfined compressive strength
of the rock
established using standard method of testing, the approach described shall
be used.
In
situations
(CR+RQD)/2
is
clayey
when
soil,
or
less than
where
strata
is
highly fragmented,
30 percent, or where
the crushing strength
is
strata
less than
is 1
where
in
directly
method
RQD
is nil
1
or
not classified as a granular or
0 MPa, the approach described
method 2 shall be used. Also, for weak rock like chalk, mud stone, clay stone, shale and other intermediate rocks, method 2 is applicable. in
MEHTOD1:
q
= u
re
+
Q allow=
r
af
= k .q cL sp ~c f
Ab
+
A C us s
(Re/3) + (R a/6)
Where, = Qu Q allow = = Re = R = Kp ,
af
s
Ultimate capacity of pile socketed into rock
in
Newtons
Allowable capacity of Pile Ultimate end bearing Ultimate side socket shear
An
empiricalco-efficient
whose value ranges from
0.3 to 1.2 as
per the table below for the rocks where core recovery
and cores tested
(CR +
for uniaxial
RQD K
is
reported,
compressive strength.
sp
2
30% 100%
0.3 1.2
CR
=
Core Recovery
RQD
-
Rock Quality Designation
For Intermediate values,
qc
=
in
Kp shall
percent
be
in
percent
linearly interpolated
Average unconfined compressive strength
of rock core
of pile for the depth twice the diameter/least lateral in
MPa 78
below base
dimension of
pile
IRC:78-2014
Ab
=
Cross-sectional area of base of
d
=
Depth factor =
f
1
pile
Length of Socket
+ 0.4 x
Diameter of Socket
i
However, value of d should not be taken more f
than
1.2.
As
=
Surface area of socket
c us
=
Ultimate shear strength of rock along socket length,
=
0.225 Vq c but restricted ,
be taken as 3.0
MPa
for other strength of
METHOD
for
to
shear capacity of concrete of the
M
35 concrete
in
pile, to
confined coudition, which
concrete can be modified by a factor V(fck/35)
2:
when cores and/or core
This method
is
applicable
geo-material
is
highly fragmented.
correlation with extrapolated
SPT
The shear
in
MPa
e
Q
aiiow
h u.b
af
obtained from
Weak
in
Very
Weak
100-60
3.3-1.9
1.9-0.7
0.7-0.4
u.s
A
its
table below:
200-100
b
c.
Weak
when
300-200
Q=R+R=C NA+C u
is
mm of penetration as given
Moderately
Approx. N Value
Shear Strength/Cohesion
strength of geo-material
values for 300
Shear Strength/Consistency
testing result are not available, or
s
= (Re/3) + (R /6) a
where
C ub
-
Average shear strength below base of
pile, for
twice the diameter/least lateral dimension of 'N'
C us
-
pile,
the depth equal to
based on average
value of this region
Ultimate shear strength along socket length, to be obtained from table,
value of socket portion. This shall be restricted to shear capacity of concrete of the pile, to be taken as 3.0 MPa for M 35 concrete in confined condition, which for other strengths of concrete can be modified by a factor V(fck/35) Intermediate values
based on average
'N'
c ub and c us can be interpolated linearly.
L =
Length of socket.
N =9. Q aiiow = Allowable c
The extrapolated values
capacity of
pile.
of 'N' greater than
300
shall
be
limited to
300 while using
this
method.
General notes 1 )
common
to
Method
1
and Method
2:
For the hinged piles resting on rock proper seating has to be ensured. The minimum in hard rock, and 0.5 times the diameter of the pile socket length should be 300
mm
79
IRC:78-2014 weathered
in
rock.
The allowable end bearing component
2)
restricted to 5
neglected.
be
shall
M Pa.
For calculation of socket
3)
by factor of safety
after dividing
The
friction
mm depth of rock shall be
the top rock 300
friction capacity,
capacity shall be further limited to depth of six times diameter
of pile.
For the termination of working piles
4)
the rocky strata methodology given
in
clause 10 can be used as a quality control
Moment
9.2
For the socketed
Carrying Capacity of Socketed Piles
pile,
the socket length
in
in
sub-
tool.
the rock
:
may be
calculated from following
equation:
L =
2H
4H
2
+
QM
where =
Socket length
H
=
Horizontal force at top of the socket
M
-
Moment
D
=
Diameter of the
/_
s
o =
at the top of the
socket
pile.
Permissible compressive strength
in
rock which
leaser of 30 kg/sq
is
cm
or
1
0.33q c In
case of socketed
.
piles, for
the satisfactory performance of the socket as fixed
rotation at the top of the socket for the fixed condition (9) should
tip,
the
be less than or equal to
5 percent of the rotation for the pinned condition at the top of the socket (9)
10 PILE
TERMINATION CRITERIA AS A QUALITY
CONTROL TOOL For establishing the similarity of
IN
soil strata actually
ROCKS
met while advancing the
the strata selected for terminating the pile on the basis of
N values
pile-bore with
equivalent energy method
can be used.
The concept
The
pile
of Pile Penetration Ratio
(PPR)
is
used
penetration ratio (PPR) reflects the energy
the pile bore of
one
sq.
in this
in
meter cross-sectional area by
80
method.
ton-meter required to advance 1
cm.
!RC:78-2014 1
case of
In
)
SPT test
PPR
its
can be worked out as follows:
Energy E spent for N blows = 63.5 kg x 75 cm x N blows (in kg - cm units) = E x 1 2 meter. Area of samples is 0.758 x (5.2) sq. cm = 21 .24 sq.cm, penetrating 30 cm.
Hence PPR = 63.5
PPR and
for
x 75 x
N
x 10
5
(21. 24x1
/
0^x30) =0.747 N
N = 50 = 37.35 tm/m 2 /cm
N = 200 =149.4 tm/m 2 /cm
for
where tm = energy
m
2
cm 2)
3)
= area = penetration
PPR
.
(P), (for
.
percussion piles) =
W
= Weight of chisel
h
-
Fall of chisel in 'm'
n
-
Number
A
= Area of
p
= Penetration
PPR
in
in
'm 2
Whn
MT
or blows of pile in
x
hammer
'
'cm'
=
(R), (for rotary piles)
2n nXt
^p
where
N
= Revolution per minute
T
= Torque
in 'tm' for
t
= time
minutes
A
- Area of piles
P
= Penetration
in
in
in
corresponding
'm 2
'
'cm'
81
'n'
5
ton
IRC:78-2014
Appendix-6 (Clause 710.1.4)
ABUTMENTS, WING AND RETURN WALLS
FILLING BEHIND
1
The type
of materials to
A general
1
guide to the selection of soils
is
given
in
General Guide to the Selection of Soils on Basis of Anticipated Embankment Performance
group according to Visual
SoiS
behind abutments and other earth retaining
for filling
1
Table
IS
be used
be selected with care.
structures, should
Table
FILLING MATERIALS
1498-1970
Most probable
description Possible
Max. dry
Optimum
Anticipated
density
moisture
embankment
range kg/
content range performance
m GW, GP, GM,
Granular
SW, HP
materials
SM, GM, GC, SM, SC
Granular
SB,
3 *
percent
1850-2280
Good
7-15
to
Excellent
1760-2160
9-18
Fair to
materials
Excellent
with soil
SP ML, MH, DL
CL, SM, Sandy
SB,
SC
19-25
Fair to
Good
Laying of
2.1 filter
& 1760-2080
10-20
Fair to
Good
Filter
LAYING AND COMPACTION Media for Drainage
material shall be well
size towards the soil
Silts
Silts
2
The
1760-1850
Sand
packed
to a thickness of not less than
and bigger size towards the
behind abutment, wings or return walls to the Filter
materials need not be provided
mm
and provided over the
with smaller
entire surface
height.
case the abutment
is
of
spill
through type.
Density of Compaction
2.2
Densities to be aimed at
the
in
full
wall
600
soil type,
and type
height of
in
compaction
shall
be chosen with due regard
embankment, drainage
to factors,
such as,
conditions, position of the individual layers
of plant available for compaction.
Each compacted
layer shall
be tested
in
the
operations for next layer are begun.
82
field for
density and accepted before the
IRC:78-2014 3 The extent
EXTENT OF BACKFILL
of backfill to be provided behind the
abutment should be as
DIRT WALL -
illustrated in Fig.
1
1
FACE OF DIRT WALL EXTENT OF
FILL-
-MAIN BRIDGE
REQUIREMENT OF 100mm NOMINAL DIAMETER PIPES SPACED AT 1.0 mc/c HORIZONTALLY AND 1.0 m VERTICALLY, PLACED IN ONE OR TWO LAYERS SEJDJLEVEL
LWL
Notes Active wedge of soil mobilized
I
2. In
in
developing active pressure has to be
case, projection of footing towards earth-fill is less than
600 mm, the
filled
by selected
filter shall
earth.
be supported near the
top of the footing.
PRECAUTIONS TO BE TAKEN DURING CONSTRUCTION
4
The sequence
4.1
of filling behind abutments, wing walls
be so controlled that the assumptions made clearly
be indicated
front of the
in
abutment
in
the design are
the relevant drawings. For example, is
assumed
simultaneously along with the
filling
the design, the front
in
behind abutment, layer
behind abutment before placing the superstructure filling
behind abutment should also be deferred
to
is
and
return walls shall
fulfilled if
the earth pressure
filling
by,
and they should
shall also
and
in
in
be done
case the
filling
considered not desirable, the
a later date.
In
case of
tie
beams
and friction slabs, special care shall be taken in compacting the layer underneath and above them so that no damage is done to them by mechanical equipment. Special precautions should be taken to prevent any wedging action against
4.2 structures,
or strutted
4.3
and the slopes bounding the excavation to prevent such wedging action.
Adequate number
of
weep
low water
be stepped
holes not exceeding one metre spacing
in
both
any accumulation of water and building up of The weep holes should be provided above the
directions should be provided to prevent
hydrostatic pressure behind the walls.
for the structure shall
level.
83
IRC:78-2014
Appendix-7 (Clause
-
709.2.4)
PART-1
METHOD-1: PILE LOAD CAPACITY BY DYNAMIC TEST USING
WAVE EQUATION This method soil
based on solving wave equation by using idealized model using
is
parameters
to arrive at pile 'set' for given pile load.
pile to
an impact force applied
(of the
order of magnitude of ultimate capacity of
capacity of
axially
by drop of
The
hammer pile)
strata
wise
force and velocity response of
causing large strain at top of
pile
are measured to arrive at the ultimate
pile.
THEORETICAL BACKGROUND For piles considering
resistance from
surrounding
soil,
the
displacements produced on segment of prismatic bar subjected the
internal
to
force
and
impact at one end,
wave equation can be derived as
where
D
=
longitudinal displacement of a point of the bar from
E
=
modulus
x
=
direction of longitudinal axis
of elasticity of bar
original position
p = density of bar material +
&R=
The above equation may be solved
for appropriate
among displacement, time,
in
position
its
t
= time
soil-resistance term
boundary conditions and the relationship
the pile and stress are determined usually by numerical
methods. Solution requires idealization of model considering load deformation diagram
each segment, the 'quake' ultimate soil resistance factor
i.e.
maximum
and the damping
deformation that can occur factor.
The
elastically, 'Ru'
empirical value of 'quake',
in
Table
1.
84
the
damping
and percent side adhesion as reported by Forehand and Reese are reproduced
reference
for
for
IRC:78-2014
Table
Empirical Values of Q,J, and Percent Side Adhesion
1
Q (in.)
Soil
J(P) (Sec/ft.
Side Adhesion
(% ofR Coarse sand odllU y idvcl
Fine
0.10 1
1
Sand
Sand and and
35
0.15
mu
U.
I
/
1
o-
1
uu
0.15
0.15
TOO
0.20
0.20
25
sand underlain by
0.20
0.20
40
gravel underlain by
0.15
0.15
25
clay or loam, at least
50 percent of Silt
n U.
HacU
fine
)
sand
pile in
hard strata
Sand and hard strata 2
PILE AND TEST
1)
The
testing should
be conducted by fixing instrumentation that should include strain sensors and accelerometers to the sides of the pile at a depth of 1 .5 x pile diameters from top of pile and then connecting them to the measuring equipment.
2)
For
this
it
is
PREPARATION
desirable that the pile
extended
is
to suitable length after chipping top
loose concrete. This can be done either using formwork or permanent casing.
two openings/windows approximately 300 mm x 300 mm and diametrically opposite to each other shall be made into the liner at 1 .5 x pile diameter from top.
Alternatively
3)
if it
is
a
liner pile,
and have same strength as pile concrete. The pile head may even be one grade higher so as to attain early strength. The rebars and helical reinforcement shall also be extended to avoid cracking of In
case
pile
head
concrete under Refer to
Fig.
1
is
extended,
hammer
for
shall
be
axial, flat
impact.
a sketch of reinforcement
bars shall generally be the
sensor
it
level shall
same as
pile
Fig.
1
:
Details of
the extended pile and the diameter of
reinforcement. Further, the concrete at the
be smooth hard and uniform.
1
Plan of Test Pile
in
.
All dimensions are in
mm
mesh reinforcement
20
2.
Clear cover to
3.
Diameter of mesh reinforcement bars
4.
Spacing of mesh reinforcement bars
is
is
is
mm. 8
mm.
100
mm.
Elevation of Test Pile
Rebar cage
for
extended portion of
85
pile for
dynamic
test
IRC:78-2014 4)
A
pile
top cushion consisting of sheets of plywood with total thickness between
mm to
25
100
mm or as determined by the Test Engineer shall be placed on the top
of the pile before testing.
5)
Steel helmet 25
mm-50
mm
determined by the Test Engineer shall be
thick or as
kept ready at the time of testing. 6)
A hammer of suitable weight (1-2 percent of test load or 5-7 percent of the dead weight of the pile whichever
is
higher) shall be used for testing the pile unless specified otherwise
by the Test Engineer. The 7)
Wherever
fall
height generally varies from 0.5
essential, a suitable guide shall
be provided
m to to
3 m.
ensure a concentric
fall.
8)
A
suitable crane or equivalent
hammer Fig.
shall
be arranged on
mechanism capable
of freely falling the required
site in consultation with the test
engineer. Refer to
2 showing the setup arrangements. TYPICAL SKETCH SHOWING SETUP DETAILS FOR HIGH STRAIN DYNAMIC PILE TESTING Single Hoc ol crane or winch or any other free (ell rnechanrsm
Drop Hemrner
Fa*H
Height
Steel helmet
Plywood Sheet -
Sensors fbcsd bsetaw epprox 1 Sfcmas p«e aim •f
Diameter same
m
pile
ooncnaa* and grade > pile concrete
Steel Liner
_ Steel
kner provided to extend the pile Can use (brmwortc Instead Liner fa optional
Re-built portion from sound concrete level or sound & smooth concrete
Sensor* Axed onto
Fig. 2: Typical
pile
concrete
sketch showing setup details for high strain dynamic
86
pile testing
IRC:78-2014
A suitable power
source supply shall be provided
sensors and
for fixing
for the test
equipment.
PILE
MONITORING
The
testing
may be conducted
and the concrete
atleast
days
15
as well as extended portion
pile
the
after
pile
installed
is
any has achieved the
if
required strength.
Dynamic
pile
attaching
strain
(based
testing
transducers
approximately 1.5 times
needs
to
the pile
if
pile
on wave equation) should
and accelerometers
diameter below the
be fixed onto opposite sides of the
the
to
pile top.
pile,
A
so as
be conducted sides
the
of
by pile,
pair of transducers
bending
to detect
/
in/
any, during testing.
These transducers should be then connected through the cable equipment
to record strain
to
measuring
and acceleration measurements and display them on an
oscilloscope or screen.
The
testing should
be conducted by impacting the
pile with
blows of the hammer,
hammer
generally starting with a smaller drop of 0.5 m. For each
blow, the strain
transducers should measure strains whereas accelerations are measured by
accelerometers connected on either sides of the converted to
digital
pile.
These signals are then
form by the equipment and then converted
to force
and
velocity
respectively by integration.
For each in
hammer
blow, the test
system should display immediate
the form of the mobilized capacity of the
stresses etc.
The
force
and
pile, pile
velocity curve shall
field results
top compression,
be generally as defined
integrity, in
ASTM
D4945. Testing should be continued by increasing height 0.5
m
increment
till
fall
of the
the time either the pile set or the pile capacity reaches the
required limiting values. Atypical force velocity response
The
pile
due
to
capacity shall be generally considered to be
hammer
hammer by approximately
fully
is
also described
mobilized
if
the energy levels
impact are sufficient so as to cause a measurable net displacement
mm per blow for a minimum three successive impacts. the less than 3-4 mm per blow and the pile achieves required capacity, then
of atleast 3-4 is
in Fig. 3.
it
that not
some
If
all
the static pile resistance has been mobilized and that the pile
capacity that could not be measured or
the time of testing.
87
was
not required to be
pile set
implies still
has
measured
at
IRC:78-2014
Fig.
8)
3
:
Typical force-velocity trace generated by measuring equipment
Analysis and Interpretation
Using strain and acceleration data
:
model, based on local parameters of
and
pile
The
load bearing capacity shall be calculated.
and
soil
strata,
considered and the safe capacity arrived.
soil
Atypical blow
then selected for Signal Matching Analysis.
is
4)
TEST LIMITATIONS
1)
Evaluation
of
variety
analytical
of
static
the
result
the
into
dynamic evaluation
calibrate
and
methods and
judgment. The input the
strata
resistance
soil
of the
it's
the
is
analytical
matching
the equivalent static
report should specffy the
final
parameters of
pile
a suitable
in
can be based on a
distribution
subject
of
individual
engineering
methods may or may not load
static
data.
test
dynamic analysis with those
It
of a
is
result
in
necessary
to
static
pile
load
test carried out according to IS 2911.
•
Based on above,
it
can be said that
and actual end bearing
for
it
is
difficult to
rock socketed
piles
predict rock socket friction
that
do not show substantial
net displacement under the impacts. Unlike
static
testing,
evaluation
experienced engineer trained
in
of
dynamic
pile
test
interpretations of the results.
88
results
requires
an
IRC:78-2014
METHOD-2: PILE DYNAMIC TEST METHOD BASED ON
FORMULAE
HILEY'S
OPERATED EQUIPMENT)
(BY LASER/INFRARED 1
INTRODUCTION
Since the early days of driven
piles,
the termination criteria based on "Sets observed", are
The
followed. Various formulae are available.
IS
Code 2911
provides one such formula. The principle followed of the
hammer, and on
of standard
numbers
- 1
of blows of
hammer, the
strength
after curing)
(i.e.
the founding strata
in
i.e.
average penetration
ultimate capacity for the pile
factor of safety the safe capacity
in-situ piles after attaining
covering driven piles
recording the penetration per blow
is
that basis having obtained the desired set
and then with suitable be advanced further
Part
(i.e.
is
arrived
is
worked out
The bored
at.
can be treated as precast
cast-
pile to
on which terminated) by dynamic
strata
impact energy. The load carrying capacity of bored cast-in-situ
pile
subjected to impact
energy can then be estimated on measuring consequent displacement by sophisticated optoelectronic instruments on resorting to IS 2911 procedure. ascertaining the quality of
workmanship on a
wasting and avoiding delays
in
a construction
number
large
of
The procedure will help in piles without much of time
activity with relatively less cost.
METHODOLOGY The methodology the elastic body.
of test
is
based on a large
weight giving the dynamic impact to
hammer blow
equates the energy of
It
falling
to
work done
in
overcoming the
resistance of the founding strata to the penetration of the ordinary cast-in-situ piles as well as grouted micro piles.
compression of the
pile,
Allowance
and subsoil as
Modified Hiley's formulae given
in
the ultimate driving resistance
in
code, the safe load on
pile
IS
Code 2911
for losses of
energy due
caused by the impact
the code IS 2911 Part
-1,
Section
I
to the elastic
of the
are used
in
pile.
The
estimating
tonnes. Applying the factor of safety as outlined
in
the
out.
including rebounds of the pile are precisely recorded
automatic data acquisition system. This in
made
well as losses
can be worked
The instantaneous displacements as accepted
is
is
done
for several cycles
the safe loading capacity
is
in
and then using formulae
The
calculated.
opto-electronic
measurement by non contact continuous measurement, using instrument placed away from the vibrations due to impact load. The instrument
system detector
is
is
for
position
based on combined
The
reference
used
transmitter
line
sensitive
light
emitting diode transmitters
and receiver are
installed
so that the infrared
from transmitter, receiver to the prism group
89
and a
reflectors.
position sensitive
beam forms
a
reflected light
is
light
The
IRC:78-2014 received and recorded 100 times per second. Using the energy transmitted to the
accounting for temporary compression of loading, the ultimate driving resistance
load for the pile
The modified
is
pile,
ground and
pile
and
dolly occurring during the impact
calculated. Applying the factor of safety the safe
is
calculated.
Hiley formula
is
:
Whq
R S+C/2 where
R
=
ultimate driving resistance dividing
it
in
tonnes.
The safe load
shall
be worked out by
with a factor of safety of 2.5.
W
=
mass
h
-
height of the free
ram
of the
in
tonnes; of the
fall
trigger-operated drop
ram
or
hammer
cm, taken
in
at
hammers. When using the McKiernanTerry type
H
=
of the maker's rated energy
be substituted
for the
operated at
maximum speed
its
product {Wh)
in
in
for single-acting
of double acting
hammers,
tonne-centimeter per blow should
the formula.
while the set
is
The hammer should be
being taken;
efficiency of the blow, representing the ratio of striking
value for
hammers, 80 percent of the fall of normally proportioned
winch operated drop hammers, and 90 percent of the stroke
90 percent
its full
energy
after
impact to the
energy of ram;
S
=
final
set or penetration per blow
C
=
sum
of the
cm;
in
temporary elastic compressions
in
cm
of the pile, dolly, packings
and ground
P
=
Mass
Where Wis
of pile
in
tonnes
greater than
Pe and
the pile
n = '
Where Wis
less than
Pe and the
90
is
driven into penetrable ground,
W + Pe
2
W+ P pile is
driven into penetrable ground.
IRC:78-2014
The
following are the values of
n.
relation to e
in
and
to the ration of
P/W
e = 0.5
e = 0.4
E = 0.32
e = 0.25
e = 0
1/2
0.75
0.72
0.70
0.69
0.67
1
0.63
0,58
0.55
0.53
0.50
0.55
0.50
0.47
0.44
0.40
2
0.50
0.44
0.40
0.37
0.33
2%
0.45
0.40
0.36
0.33
0.28
3
0.42
0.36
0.33
0.30
0.25
0.39
0.33
0.30
0.27
0.22
4
0.36
0.31
0.28
0.25
0.20
5
0.31
0.27
0.24
0.21
0.16
6
0.27
0.24
0.21
0.19
0.14
7
0.24
0.21
0.19
0.17
0.12
8
0.22
0.20
0.17
0.15
0.11
Ratio of
P/W
%
1
3V, 2.
P is the weight of the Where the
pile, anvil,
helmet and follower
(if
any)
in
tonnes.
Pshould be substituted for Pin the above expression
pile finds refusal in rock, 0.5
for n-
e
a)
is
the coefficient of restitution of the materials under impact as tabulated below.
For steel ram of double-acting pile,
b)
striking
For cast-iron ram of single-acting or drop pile,
with hard
Numbers
anvil
and
driving reinforced
hammer
striking
on head of reinforced
e = 0.4.
Single-acting or drop
pile,
on steel
e = 0.5
concrete c)
hammer
wood
hammer
striking a well-conditioned driving
dolly in driving reinforced concrete piles or directly
cap and helmet
on head of timber
e = 0.25.
of
models
of Laser/infrared operated instruments
measuring accurately the
deformation are available these days. The required sensitivity of the equipment shall
be such as
to
read the angular deformation to the accuracy of 10-3 radians and the
instrument should be capable of recording about 100 readings per second. From the
angular deformation, on knowing the distance of the reflector from the instrument, 91
!RC:78-2014 Typical Displacement Record
400
s
-
600
-0.4
5 -0.5
-
-
«y
% 5
500
-°- 6
f—
--
—
-
—
—
U
r
1
-
-
H
-
1
i
l„
-0.7 -0.8 -0.9
Reading Serial Number.
vertical
movement
of the shaft under the given impact energy, (both elastic
and
permanent) can be measured accurately. These measurements of the displacement can then be substituted
in
modified Hiley's formulae stated
in
IS 2911.
The
ultimate
load carrying capacity of the pile can be worked out, resorting to the modified Hiley's
formulae outlined
in
the code and from that the safe load carrying capacity of pile can
be estimated.
92
IRC:78-2014
Appendix-7 PART-2
STANDARD TEST METHOD FOR LOW STRAIN 1
Pile Integrity Testing (PIT)
is
PILE INTEGRITY TESTING
SIGNIFICANCE AND USE
a Non-Destructive
method
integrity test
for foundation piles.
The method evaluates continuity of the pile shaft and provides information on any potential defects due to honeycombs, necking, cross-section reduction, potential bulbs, sudden changes in soil stratum, concrete quality in terms of wave speed etc. It is known as "Low requires the impact of only a small hand-held hammer and the Strain" Method since resultant strains are of extremely low magnitude. The test procedure is standardized as per ASTM D5882 and also forms part of various specifications and code provisions worldwide as indicated in Table-3. The number of tests shall be decided by the engineer to the project. it
Table 3 Major Standards or
Sr no
Method
D
LST,
CSL
Codes
for Integrity Testing
Country
Reference
Title
Australia
Australian Standard
Pile
As
Designing and
installation
21 59-1 995
Technical
code
Chapter
Piles foundations
2)
LST,
CSL
China
JG J 94-94
Building
for
9:
Inspection and Acceptance of
-
pile
Foundation
9.1
Quality Inspection of Pile
Engineering.
installation.
3)
LST.CSL
China
Specification
JGJ 93-95
Dynamic Testing
4)
LST
France
Norms Francaiso
LST.CSL
Germany
DGGT
investigation
testing
ascnliation
LST.CSL
UK
and of buried
by
reflection
Empfohlung Integritataprufungen
6)
Strain
of Piles.
Soil
work method impedance 5)
Low
for
Institution
of
Civil
-
Specification of Piling.
Engineers. (ICE) 7)
LST
USA
ASTM D5882
Standard specification Strain Piles.
93
Imaginary
for
Low
Testing
of
IRC:78-2014
TYPICAL METHODS
2
Various methods used to evaluate the integrity of the
The evaluation
are briefly described below.
pile
can be described as follows.
of PIT records
Pulse-Echo Method
(or
Sonic Echo
-
a time domain analysis)
Force Velocity Approach
The Force
maybe
Response Procedure (Frequency Domain Analysis)
•
Transient
•
Cross Hole Sonic Logging Velocity approach
difficult to
evaluate
used method and
is
in
sometimes used
is
Pulse Echo Method. The Pulse Echo
test
Tester or any equivalent that meets
digital
ASTM D5882
must be displayed
in
and a
should be possible.
the
be conducted
engineer/technician. sufficient
space
for
like
at least 7
The equipment must also non-instrumented hammer etc. The data
days
after pile concreting
at the pile top surface
an accelerometer onto the
candle wax, vaseline
with a hand-held device (a hand-held
at least 3 locations,
smaller diameter piles.
The
wp*c T
ASTM
top (not near
smooth
with
impact area. The its
attachment, the
edge) with the
pile is
piles of
testing. All
600
whereas minimum one
typical data sets for in
relatively
hammer
blows during the stage of
may be conducted on
also defined
pile
etc. After
blows are averaged before display. For larger diameter
impacted
good or damaged
mm
such similar
and above testing
location
pile shall
is
enough
DEPTH
IN
D5882.
pice
m
PIT Velocity versus Depth
plot for
normal
94
pile
OCPTH
for
generally be as
roe RESPONSE
PILE
Fig. 1:
must be
by an experienced
hammer).
test involves collection of several
is
a Pile Integrity
like
requirements.
attachment of the motion sensing device and
help of bonding material
per Fig.1 and
commonly
TEST PROCEDURE
The concrete
testing involves attachment of
The
top that
evaluations of preliminary data quality and interpretation
field for
4 testing shall
the most
data acquisition equipment
include a sensitive accelerometer, instrumented or
The
is
pile
TEST EQUIPMENT
should be performed using
field printout
near the
described below.
3
The
to evaluate defects
IN
(Top) and defective pile (bottom)
IRC:78-2014
5
The
final
REPORT SUBMISSION
report shall include the following:
1 )
Project Identification
2)
Test
&
Location
and Concrete Mix as per 3)
Type
4)
Description
of Pile
of special installation procedures
components
the
all
area
Cross-Sectional
installation record
and description of
Nominal
Length,
including
Identification
Pile
of
measurements and recording/displaying
apparatus
the
used
for
if
any.
obtaining
integrity
data.
5)
Graphical representation of Velocity measurements
6)
Comments on
7)
Comments on any
8)
Comments on
in
time domain.
the quality of the Pile Concrete. potential
defects/damage and
Integrity of Pile
its
location.
based on above.
6 LIMITATIONS Certain limitations are inherent
in
the low strain test
treated only as an indicator of quality of work
method and hence
and not as a conclusive
mentioned below must be understood and taken
test.
into consideration in
it
The
should be limitations
making the
final
integrity evaluation.
1)
Integrity
evaluation of a
pile
cross-sectional
not
possible
since
pile
area the
or
section
a
impact
below a crack
manufactured
wave
likely
that
mechanical will
reflect
crosses the entire joint
is
completely
normally at
the
discontinuity.
2)
Piles
with
difficult to
3)
highly
variable
cross-sections
or
multiple
discontinuities
maybe
evaluate.
The method
is
intended to detect major anomalies and minor defects
may
not be detected by this method. 4)
The
test
is
not applicable to jointed
pre-cast piles or hollow steel pipes or
H-sections. 5)
The method cannot be used
to derive the pile capacity.
95
(The Official the IRC
amendments
to this
in its periodical,
document would be published by
Indian Highways' which shall be
considered as effective and as part of the code/guidelines/manual, etc.
from the date specified threin)
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