Shallow Foundation Settlement (Clay) - Tut 6

Geotechnical Geotechnical Engineering Settlement of a Shallow Foundation in Clay Principles

The settlement of a foundation on clay is dependent on the load applied, the direction of the applied load, the point of application of the applied load, the period over which the load is applied the depth of the foundation, the plan area of the foundation, the width of the foundation, the position of the round water level, the profile of the ground water pressure, the thickness of the soil layers, the unit weight of each soil layer  the stiffness of the soils and the time the load is applied.

'&& k3

Harrs solution Settlement, s

=

 D  f  

(1 −ν 2 ) lay  NC  ' q n B I  p  E  * m / γ   = 1 kN 

cU  = 0&kPa  B ×  L

qn

= B =

!readth of foundation

p =

"nfluence factor 

E =

#odulus of elasticity

=

qn

2 = &./(min *contact mv increase  MN ) stress [note it is the net increase in stress that causes settlement

=

$oisson s ratio (% &.' for immediate settlement in clay) ’

&& (2)( 2)

=

− (1)(1)

1&k$a

p =

&. for !*+ % 1 and  - one of influence

E =

2'#$a

s =

Correction for rigid foundation

(1 − &. 2 ) (1&)( 2) & . 2

=

'.2mm

=

&.

settlement = =

(&.)('.2) !"#mm

Christian and Carrier Settlement, s =

qn

= B =

u1u & q n'  B  E d 

net increase in contact stress [note it is the increase in stress that causes settlement !readth of foundation

o

=

"nfluence factor fro depth correction

$

=

"nfluence factor for correction for shape and one of influence

Ed =

qn

=

#odulus of elasticity

&& (2)( 2)

=

1&k$a

For %&B = '"(,

o

=

&.

For H ) *one of influence,

$

=

&.

s =

− (1)(1)

(&.)(&.)(1&)(2) 2

=

4.mm

Correction for rigid foundation

&.

=

(&.)(4.)

settlement = =

+"#mm

ong term settlement using consolidation theory

The procedure is to5 divide the soil into layers calculate the effective over6urden stress at the centre of each layer calculate the increase in stress at the centre of each layer  use 7adum s charts for increase in stress at the corner of a rectangle for settlement at centre divide the rectangle into four  calculate the change in thickness of each layer  ’

'

settlement =

mV  q n  H 

∑ 4 I ∆

=

mv h

coefficient of volume compressi6ility

m- =

thickness of layer 

h =

"ncrease in stress in layer due to contact stress

=

-

'

σ  v

8ccording to 7adum9s charts :epth  6elow foundation (m)

Thickness

;ver    6urden  pressure (k$a)

$our   press ure (k$a)