Question

A consolidation test was performed on a sample of fine-grained soil sample taken from a depth such that the vertical effective stress at that depth is 154 kN/m2. The thickness of the layer is 8 m, and the preconsolidation stress of the fine-grained soil layer is 154 kN/m2. If the initial void ratio of the soil is 0.87 and the design load to be added at the surface will induce a change in stress of 28 at the depth the sample was taken, calculate the primary consolidation settlement expected due to that load. The compression index of the soil is 0.3, and the recompression index of the soil is 0.07.

Answer 1

Answer:

The settlement that is expected is 1.043 meters.

Explanation:

Since the pre-consolidation stress of the layer is equal to the effective stress hence we conclude that the soil is normally consolidated soil

The settlement due to increase in the effective stress of a normally consolidated soil mass is given by the formula

$\Delta H=\frac{H_oC_c}{1+e_o}log(\frac{\bar{\sigma_o}+\Delta \bar{\sigma }}{\bar{\sigma_o}})$

where

'H' is the initial depth of the layer

$C_c$ is the Compression index

$e_o$ is the inital void ratio

$\bar{\sigma_o}$ is the initial effective stress at the depth

$\Delta \bar{\sigma_o}$ is the change in the effective stress at the given depth

Applying the given values we get

$\Delta H=\frac{8\times 0.3}{1+0.87}log(\frac{154+28}{154})=1.04$