Question

The following are the results (in kPa) of a consolidation test for a clay with a current effective stress of 400 kN/m². Calculate the primary consolidation settlement of the 5-m thick layer if the initial void ratio is 1 and the increase in the overburden pressure is 400 kPa. (Hint: max curvature at 150 kPa) log o' 1.21 1.195 1.15 1.05 0.97 500 0.85 0.6 1000 2000 0.2 1000 500 0.28 0.36 0.42 300 0.82m 0.68m 0.94m

Answer 1

Primary consolidation settlement is given by

CH Ovo + 40 Sc= 1+ en logo '

where,

S_c is settlement

C_c is compression index

H is the thickness of clay layer

$$${{e_0}}$$$ is initial void ratio

$$${{\sigma _{v0}}'}$$$ is initial effective stress

$$${\Delta \sigma }$$$ is increase in overburden pressure

Compression index is given by

e logo - log ovo

where,

$$${\Delta e}$$$ is change in void ratio

$$${{\sigma _v}'}$$$ is final effective stress

$$${{\sigma _{v0}}'}$$$ is initial effective stress

The sample values are calculated as

Initial void ratio is given as 1.

Initial effective stress is given as 400 kN/m²

Increase in overburden pressure is given as 400 kPa

So, change in void ratio will be

Le = 1.21-1=0.21

Ce = log(ocoʻ+)log Ooot 0.121 log (400+400)-log 400 = 0.4

The thickness of clay layer is given as 5 m.

Se=log $c = 9:45. log 100.00 Se=0.3m

Similarly all the values are calculated as

Δe Сс 1.21 1.195 1.15 1.05 0.97 0.85 0.6 0.2 0.28 0.36 0.42 0.21 0.195 0.15 0.05 -0.03 -0.15 -0.4 -0.8 -0.72 -0.64 -0.58 0.4 0.648 0.498 0.166 -0.09966 -0.498 -1.33 -2.66 -2.39 -2.126 -1.927 Sc(m) 0.301029996 0.487668593 0.374782345 0.124927448 -0.07500162 -0.37478234 -1.00092474 -2.00184947 -1.79865422 -1.59997443 -1.450212