Question

While increasing the pressure to 150 kPa from 50 kPa, the change in void ratio of soil is observed as 0.12 in a consolidation test. The compression index of soil is
1. 0.03
2. 0.06
3. 0.25
4. 0.19

Answer 1

Correct Answer - Option 3 : 0.25

Concept:

Compression index:

(i) If void ratio is plotted on y-axis on airthmetic scale and effective stress on log scale on x-axis, then the curve for normally consolidated clays is found to be straight line.

(ii) The slope of this curve is constant, which is called coefficient of compression or compression index

Coefficient of compression,

\({C_c} = \frac{{Δ e}}{{\log \left( {\frac{{{{̅ σ }_2}}}{{{{̅ σ }_1}}}} \right)}}\)

Calculation:

Given,

Δe = 0.12,  σ̅₂  = 150 kPa,  σ̅1 = 50 kPa

∵ Compression index, \({C_c} = \frac{{Δ e}}{{\log \left( {\frac{{{{̅ σ }_2}}}{{{{̅ σ }_1}}}} \right)}}\)

\({C_c} = \frac{{0.12}}{{\log \left( {\frac{{150}}{{50}}} \right)}} = 0.251\)