Presentation by Sandeep Pattiwar, TANGENT Technical Solutions to Power Grid Corporation of India Limited, Gurgaon Date: 8th February 2010
Well Foundations in India Introduction y In large parts of India, well foundations are commonly
adopted for bridges y Design and construction practices have been progressively streamlined to cater for ever increasing progressively streamlined to cater for ever‐increasing loads and foundation depths y With the introduction of large spans, the well size also With the introduction of large spans the well size also increases. For Second Hooghly Bridge, 24 m dia wells have been adopted The deepest well so for have been adopted. The deepest well so for constructed in India is up to 70 m below WL
Well Foundations in India Introduction y Daring efforts are on in different parts of the world to y y y y
build bridges on a very large scale Even bridges between continents are in process, America Asia, Europe‐Africa for example America‐ Asia Europe Africa for example In India hundreds of thousands of bridges have been constructed during the twentieth century During the first decade of this century, about R Rs.100,000 cr are expected to be spent on Bridges t d t b t B id Foundations cost 50 % or more
Use of Well Foundation Introduction y Past Experience making it more reliable and y
y y y
dependable by virtue of default choice Well foundations are more suitable for deep water where it is difficult to carry construction equipment like River/Creek Bridges Intake Structures offshore as well as river Intake Structures, offshore as well as river Deep foundation and suitable for alluvial soil which mainly consist of Sandy i l i t f S d No special equipment and heavy machineries are required i d
Use of Well Foundation Introduction y Used in India and Indian Sub‐continent only y Well Foundation is preferable to pile foundation if it W ll F d i i f bl il f d i if i
has to resist large horizontal forces y Well foundation is more suitable for deep water where W ll f d i i i bl f d h it is difficult to carry construction equipment y Well Foundation is meant for deep foundation where W ll F d i i f d f d i h the river bed gets scoured and forces need to be t transferred to deeper level. f d t d l l
Pile Foundation Vs Well Foundation Item
Pile Foundation
Well Foundation
Vertical Capacity
By Side Friction as well End Bearing
Only End Bearing
Lateral Capacity
Net balance of Passive By Fixity Depth in clay as well Sandy Soil, alternatively Resistance and Active Spring Analogy can be used Pressure with FOS of 2
Structure
Slender and Flexible
Short and Rigid
Construction
Difficult under deep water
Easy comparatively
Construction Equipment
Heavy and Costly like Rig p and platform
Crane and Grab
Time
Faster
Longer
o ec o Protection
Liner is required up to scour e s equ ed up o scou level
Ca sso s equ ed if Caisson is required necessary for construction requirement
DESIGN ASPECTS
Shapes and Sizes Shape is governed by the requirement of stability during construction and least resistance during service: y Need for effective streamline flow y Circular is the most common option available y D‐Shape well for wider and heavy foundations y Rectangular shape is rare unless required for the functionality y Circular diameter is upto 12 m without any diaphragm else either diaphragm is provided or extensive study is undertaken for the steining stresses.
Shapes and Sizes Shape is governed by the requirement of stability during construction and least resistance during service: y Dredge hole for easy dredging > 2 m y D‐Shape well is not to have
aspect ratio (length/breadth) 2:1
Well Foundation A Well foundation consist of following components: y Cutting Edge y Well Curb W ll C b y Bottom Plug y Steining y Sand Filling y Top Plug y Intermediate Plug y Well Cap
Input Data y Forces above well foundation y Hydraulic Parameters like scour depth, current Hydraulic Parameters like scour depth current y y y
y
velocity and Discharge Seismic Zone and Wind Pressure Bore Hole details for assessing depth of soil and rock, if anyy Geo‐technical Investigations including stratification, y and c and weighted mean diameter of bed g density, φ material Bearing Capacity
Special Requirement y y y y y
Variation of depth of water i.e. HFL and LWL Bed Levels and Ground Levels Working Months availability Formation Level Any other feature depending on the location like rock slope type of water and moderate/severe slope, type of water and moderate/severe environment condition y Pneumatic Sinking in case of deeper founding level with boulder strata y Floating caisson incase of deep standing water g p g
Depth of Well Foundation for Soil y Mean scour depth is calculated as per bed material d sm
⎛D = 1.34⎜ ⎜k ⎝ sf
2 b
1/ 3
⎞ ⎟ ⎟ ⎠
y This “mean scour depth” is used to calculate Maximum
scour depth to account local scour effect y For Pier foundations : 2 x dsm from HFL y For Abutment foundations: 1.27 x dsm from HFL
y Grip Length: The minimum depth of foundation
below scour level is 1/3 rd of Maximum Scour Depth
Depth of Well Foundation for Rock y The well foundation shall be taken up to sound rock
and rest evenly along the periphery by blasting or pneumatic sinking, if required. y The shear key should be provided inside the rock for a depth of 300 mm in hard rock and 600 mm in soft rock. rock y Diameter of shear key must be minimum 1.5 m or 1.5 m to 2 0 m less than dredge hole to 2.0 m less than dredge hole. y 6 dowel bars of 25 mm diameter with anchored 1.5 m in rock and projected 1 5 m above in rock and projected 1.5 m above.
Well Steining Thickness of well steining is governed by following factors: y Natural sinking or sinking without excessive kentledge y Without getting damaged during rectifying excessive tilt and shift y Hoop compression for the differential pressure during p p p g construction and service y Hoop tension arising out of differential earth pressure g developed during sand blow y Structural design at all levels due to external forces
Well Steining Thickness of well steining is governed by following factors: y The minimum thickness > 500 mm y The thickness arrived for self sinking, empirically: h = kd l
y Where k is a constant and depends on the type of well
steining i i
In Cement Concrete
0.03
Twin D wells
0.039
y d is diameter of well or smaller dimensions in D‐Well y l is depth of well below top of well or LWL, which ever p p
is higher
Well Steining Further steining thickness shall be adjusted as per type of soil stratum:
Well Steining Steining thickness can be reduced if the be reduced, if the height of well is more than 30 m However than 30 m. However, the reduced diameter of well should be able to support structure above well foundation.
Well Steining – Structural Design y Plain Concrete Wells y Vertical Reinforcement = 0.12% of Gross Area V ti l R i f t % f G A y Horizontal Hoop Reinforcement = 0.04% of volume y RC Concrete Wells RC C W ll y Vertical Reinforcement = 0.2% of Gross Area y Inner Face, vertical reinforcement = 0.06% y Transverse Reinforcement as per column design and shall not be less than 0.04% of volume h ll b l h % f l
Well Steining – Structural Design y Checking of steining stresses at all critical sections and
normally these are: y Well cap bottom level y At the level of change in steining thickness At th l l f h i t i i thi k y Below scour level where resultant shear is zero
y Well steining also shall be checked for ovalisation
moments t
Well Steining – Jack down method Well Steining Jack down method •
As per ‐IRC‐78‐2000 Clause‐708.2.3.5 l If Specialised methiods of sinking such as jackdown method are adopted then the steining thickness may be adjusted according to design and construction requirements. i t
Check for cohesion‐less soil y IRC 45 recommends checking of well
Side Earth Resistance y Active and Passive Earth Pressure as per Coulomb
Theory:
Side Earth Resistance y In case of c‐φ soil, effect of ‘c’ may be added as per
procedure given by Bell:
Bell Correction
Side Earth Resistance – F.O.S. y The Side earth resistance for pier wells is considered
below scour level y The resistance calculated is ultimate and converted into allowable resistance by dividing F O S into allowable resistance by dividing F.O.S. y Net pressure of Passive and Active is calculated y F.O.S. is considered 2 for load combination without F O S i id d f l d bi i i h
wind or seismic y F.O.S. is considered 1.6 for load combination with wind F O S is considered 6 for load combination ith ind or seismic
Side Earth Resistance y For cohesionless soil, IRC 45 may be used for pier well
foundations y Side earth resistance may be ignored in case of foundations resting on rock y However, side resistance of well foundations resting on rock be considered if allowable bearing pressure is less than 100 t/m2
Tilt and Shift y In Design of well, tilt of 1 in 80 and shift of 150 mm due
to translation both additive in a direction which will cause most severe effects shall be considered y If the actual tilt and shift exceeds the above limits, , remedial measures have to be resorted to bring the well within limit. y However, if not possible then its effect on bearing pressure, steining stresses shall be examined and if necessary can be sink further down to control the base pressure.
Cutting Edge y To penetrate easily through the different type of strata
cutting edge is provided at the base of well. It is cutting edge is provided at the base of well It is designed to cater resistance which encountered during sinking It shall be anchored properly to well curb sinking. It shall be anchored properly to well curb. y Guidelines of IRC 78 stipulate that its weight should not be less than 40 kg/running meter. not be less than 40 kg/running meter y When there are partitions, the intermediate cutting edge have been placed 300 mm higher than the outer cutting edge to prevent rocking.
Cutting Edge
Cutting Edge
Cutting Edge g g
Cutting Edge
Required 40 kg/meter
Well Curb y Minimum resistance while being sunk. y Strong enough to transmit forces from steining to the S h i f f i i h
bottom plug y Minimum reinforcement = 72 kg/m3 y Internal angle of curb shall be kept in between 30 degree to 37 g 37 degree.
Well Curb
Well Curb
Well Curb
Bottom Plug y Is provided to transfer the load from steining to
bottom plug and ultimately from bottom plug to underneath strata. y A suitable sump shall be made below the level of the cutting edge. y Before concreting, it shall be insured that its inside Before concreting it shall be insured that its inside faces have been cleared thoroughly.
Bottom Plug
SAND FILLING
Bottom Plug
Well Cap y The bottom of well cap shall be as low as possible
taking into account of LWL taking into account of LWL. y Well cap design is as per any rational method y Normally design is cater to consider partial fixity at the N ll d i i id i l fi i h junction to take care large fixity moments.
Filling y Filling if required shall be sand or excavated material
free from organic matter free from organic matter. y Incase filling is not done, bottom plug shall be checked for upward thrust. checked for upward thrust y Normally, if vertical pressure is within limit, filling is done upto scour level atleast. scour level atleast y In a high seismic area, filling is avoided above scour l l level.
Construction of Well Foundations: Conventional Construction on
Land / Sand Islands Floating Caissons Jack down method k d h d Pneumatic Sinking P ti Si ki
Conventional Construction on Land / Sand Island Method
Well Sinking – Sand Island Method
Well Sinking – Sand Island Method
Well Sinking – Sand Island Method
GANGA BRIDGE AT PATNA
Floating Caissons Floating Caissons
Floating Caisson g z
Area for fabrication of steel caisson will be made near the river bank by constructing suitable cofferdam
z z
IInitial i i l lift lif off steell caisson i will ill be b fabricated f bi d on a leveled ground in fabrication yard G bbi off soil Grabbing il from f within i hi andd aroundd the h caisson will be carried out so as to allow the water to rush in and make the caisson to float. float The caisson will be held in position with proper guying arrangement
z z z
z
The caisson will be towed to the desired location and aligned properly Caisson will be held in position with tethering arrangement Concrete quantity as per design requirements will be poured evenly in the curb portion so that the caisson i gets further f h immersed i d in i the h water Next lift of steel caisson will be built and concrete quantity i off designed d i d amount will ill be b pouredd inside i id the caisson
z z z z z
This procedure will continue till the cutting edge comes near the th riverbed i b d When the caisson is about to get grounded its alignment will be rechecked Water will be poured inside the caisson to ensure its grounding at exact location Water ba Wate ballast ast will w be replaced ep aced with w t concrete co c ete so that t at caisson gets grounded at its exact location Steining concreting will be continued further and the well will be taken to its founding level as per normal practice
Tethering arrangement General Details
Caisson Aligned at location
First lift of concrete poured
Shifting of concrete over Barge g
Concrete placing
Build next lift of Caisson And place concrete
Checking of alignment with water ballast
Muck removal by grabbing
Sinking in progress
Steining Concreting & sinking
Sinking in progress
Final stage – At founding level
Well Caisson Launching
Caisson Fabrication Yard
Launching of Caisson
Well Caisson Launching
Caisson being towed to location
Sinking in progress
SECOND HOOGHLY BRIDGE Enabling works for caisson sinking
JOGIGOPHA BRIDGE Slipway for Floating Caissons
Jogighopa Bridge Slipway for Floating Caissons
Jogighopa Bridge Floating Gantry for Handling Caissons
Floating Caisson being g g Towed to Location
Colcrete arrangemen f ffoundation for d ti
Jack Down Method Jack Down Method
Well Sinking By Jack Down Method
Well Sinking By Jack Down Method
Well Sinking By Jack Down Method
Well Sinking By Jack Down Method
Pneumatic Sinking Pneumatic Sinking
Pneumatic sinking Pneumatic sinking y Pneumatic sinking is resorted to when open sinking
can not be continued in hard strata and excavation by open grabbing and chiseling is not possible. y When p pneumatic sinking g is adopted, p , it is p possible to inspect the well from inside and take the decision based on the actual conditions.
Pneumatic Sinking
• •
In this method airtight cover is fixed on dredge hole and compressed air is pumped in, so that water is pushed out of well up to cutting edge level. Men are sent inside to carryout manual excavation. Muck is removed through shaft without releasing pressure. . . .Contd.
Arrangement for Pneumatic Sinking
Kali Bridge – Pneumatic Sinking
Kali Bridge – Pneumatic Sinking
Limitations • Pneumatic sinking is very costly and is resorted to
only when the well can not be founded safely with open sinking. sinking • Men have to work under compressed air, air pressure of
which depends upon the depth of cutting edge below the water level. level • Depth up to which pneumatic sinking can be done
without undue risk to human lives is restricted to about 30 m. m ….contd
Limitations • Man feels increased pressure on ear drum when inside
the airlock. airlock If it is not balanced properly it may result in sever pain, bleeding and may cause damage to ear drum. • Dizziness, double vision, incoherence of speech are
quite common and some times man becomes unconscious after coming out of well.
. . . contd
Limitations • Due to the physiological effects on men working inside
an air lock, lock effective working hours are generally restricted to about two hours. This is followed by period of gradual decompression and a minimum rest period of 5 to 6 hours
CASE STUDY Second Hooghly Bridge
Second Hooghly Bridge
Second Hooghly Bridge
Second Hooghly Bridge g y g
Second Hooghly Bridge , Calcutta Tilting Slipway for Floating Caisson Tilting Slipway for Floating Caisson
Second Hooghly Bridge , Calcutta
SECOND HOOGHLY BRIDGE
Vidyasagar Setu Culcutta (1992) Vidyasagar Setu, Culcutta (1992)
Sinking a Pylon caisson 11
CASE STUDY Jogighopa Bridge
CASE STUDY Jogighopa g g p Bridge g
Brahmaputra Bridge, Jogighopa, 2.28 km
y Wells 7 and 13 tilted; more than a year to correct y Wells 17 & 18 on hard rock at steep incline (1:1). 12 x W ll & 8 h d k i li ( )
1500 mm dia anchor piles, provided through steining, extending to 10 m below cutting edge y For well 17 additional 1500 dia, 8 nos, external piles provided integral with the well cap provided, integral with the well cap y Two rows of jet grouted piles around periphery of the steining as curtain wall t i i t i ll
Brahmaputra Bridge, Jogighopa ∅ 1.5 m
WELL CAP
3.5 35m 1.5 m
50 m 2.5 m 18 m
RC PLUG
PLAN
DRILL PIPE WITH AIR CONTROL VALVES WORKING PLATFORM CASING DRILL PIPE STABILIZER + 35.00 m CAISSON STEINING AIR - LIFT DRILL PIPES HEAVY DUTY STIFF ASSEMBLY HEAVY DUTY STABILIZER
CC PLUG
3m JET GROUT CURTAIN
∅ 1.5 m PILE
STIFF SPACER PIPE NON ROTATING DRUM STABILIZER - 12.50 m
10 m
FIG. SECTION
JOGIGHOPA BR. FOUNDATIONS
DRILL BIT
WIRTH DRILLING RIG
Jogighopa Bridge – Caisson Fabrication
JOGIGOPHA BRIDGE Sli Slipway ffor Fl Floating ti Caissons C i
Jogighopa Bridge Slipway for Floating Caissons
Jogighopa Bridge Floating Gantry for Handling Caissons
Jogighopa Bridge Floating Gantry for Handling Caissons
Jet Grouting
Foundation scheme for wells 17 and 18 Foundation scheme for wells 17 and 18 Design & construction of above b f foundations, d i were governed by following main factors: (i) Likely scour upto rock strata. (ii) Uniform support over steeply sloping strata (iii) Sinking under pneumatic condition was not feasible
Foundation scheme for wells 17 I In view i off above, b f ll i following and 18 d 8 scheme was adopted :
(i) Sink well upto one metre
above top of rock strata. (ii) Stabilise S bili soil il around d well ll curb above rock strata by forming grout barrier. barrier (iii) Support steining by constructing g six out of twelve 1.5 m diameter RC piles through 1.65 m diameter holes kept in well steining, with 10 m anchor length g in rock strata.
Foundation scheme for wells 17 and 1 (iv) Remove sand in dredge‐hole b grabbing by bb and d air‐lifting lf to clean entire area including g that below well curb. (v) Construct concrete bottom plug. plug (vi) Construct balance six piles to complete anchoring of the foundation. foundation (vii) Construct RC plug over the plug g in dryy bottom p condition d after f dewatering d the h well.
Jogighopa Bridge - Piling
Piling through the Well Foundation
CASE STUDY Nepal Bridge
Artesian Conditions Shivganga bridge, Nepal, 8 spans x 32 m y Artesian head encountered at 17 m below GL y Well redesigned with foundation resting on clay above W ll d i d i h f d i i l b
the artesian layer. Plus bed protection : Upstream & downstream aprons & Cut‐off walls, U & d & C ff ll Concrete floor
Artesian Conditions - Khara Bridge, Nepal
Well disappears during sinking Artesian Bubbles
SAR 6 Y2k
CASE STUDY Passighat Bridge
Passighat Bridge, Arunachal Pradesh Well Foundation y Non availability of formula for scour depth in bouldary
strata; slow sinking in such strata y Subsoil with large boulders 2 to 3 m dia; rate of sinking 10 to 20 mm per hour initially p y y Sinking very difficult due to large size boulders; considerable slow down in overall progress y Difficulties in finally deciding the foundation level; decision making body in considerable dilemma y ‐R K Dhiman IABSE colloquium 1999 foundations for major
bridges
Passighat Bridge, Arunachal Pradesh Well Foundation y Design consultant recommended 50 m deep wells y The bore data indicated hard conglomerate right Th b d i di d h d l i h
through the depth up to 50 m except top 10 m y Core recovery was close to 90% C l % y During execution, impossible to sink the well beyond 10 m with conventional method i h i l h d y Pneumatic sinking used up to 30 m; beyond that it is not possible physiologically to work under compressed bl h l ll k d d air, it is not permitted as per code
Well Foundation Delays Passighat Bridge, Arunachal Pradesh, 703 m long Bridge Arunachal Pradesh 703 m long y Started in 1987 and well
sinking continues (2006) y Design envisaged, 50 m deep wells. Hard p conglomerate strata with very large boulders did not permit sinking it i ki y After 15 years of struggle including pneumatic sinking, the founding level was raised by 22 m. y
Boulder dredged during sinking i ki
Pasighat Bridge Unsuitable foundation design g Boulder B ld dredged g during well sinking SAR 6 Y2k
Fi 1 : PASSIGHAT BRIDGE Fig: LEGEND
Constructability
Bridge in Nepal
Narmada bridge, Chandod Well cap 14 m below water
SAR 6 Y2k
Construction Equipments Construction Equipments
Batching Plant on Shore
4/2/2010
Floating Batching Plant
Concrete cofferdam being towed to location
Cranes for Concreting and Dredging
4/2/2010
Floating arrangement for Batching Plant Concrete pump and placer boom
GANGA BRIDGE AT PATNA Fl Floating i crane for f well ll sinking i ki
Well sinking by cranes and grabs
SECOND HOOGHLY BRIDGE Enabling works for caisson sinking
Correction of Tilt and Shift Correction of Tilt and Shift
Well sinking ;Tilt correction Concrete Kentledge blocks Kentledge for Well Sinking
Wellll sinking W i ki ;Tilt Tilt correction ti Platform for concrete kentledge
Tilt Rectification of Wells
Tilt Rectification of Wells Til R ifi i Tilt Rectification of Wells f W ll
Tilt Rectification of Wells
Tilt Rectification Platform for Well Foundation
Tilt Rectification Platform for Well Foundation
4/2/2010
Kandroor Bridge across Sutlej - Badly tilt d well tilted ll being b i corrected t d
SAR 6 Y2k
Kandroor Bridge
SAR 6 Y2k
Select IRC Papers reporting Well Select IRC Papers reporting Well Foundation Problems y IRC Paper 253 ‐ Rupnarayan Bridge, West Bengal
293 ‐ Bassein Creek Bridge, Mumabi B i C k B id M bi 314 ‐ Godavari Bridge, Maharashtra
328 ‐ 8 Bhakla Bridge, UP Bh kl B id UP 359 ‐ Haldi Bridge, WB 400 ‐ Hasdeo Bridge, Champa, MP 434 ‐ Tapi Bridge, Idgaon, Maharashtra 464 – Kalyani Bridge, WB y Indian Highways, Dec 1982, Arjun Khola Bridge, Nepal
Conclusion y The construction of wells have not always been
smooth, a variety of problems during construction has th i t f bl d i t ti h resulted in inordinate delays, increased cost of rectification and even abandonment of wells tifi ti d b d t f ll y With advance methods of geo‐technical investigation,
equipments, revised codal specifications and sound engineering practices, we should able to decide the methodology and foundation type in advance.
Comments, queries, suggestions q gg
welcome tangent g
[email protected] @
