The compression index of soil-

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The compression index of soil-
1. increases with an increase in the liquid limit.
2. decrease with an increase in plastic limit.
3. none of these
4. decreases with increase in liquid limit.

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Correct Answer - Option 1 : increases with an increase in the liquid limit.

Explanation:

For undisturbed low to medium sensitivity soils, the coefficient of compression or compression index (Terzaghi and Peck empirical index)

Cc = 0.009(LL - 10)

For disturbed low to medium sensitive soil (Skempton's empirical index)

Cc = 0.007(LL - 10)

So, If the liquid limit is increased then, the compression index of soil will increase.

Compression Index:

• The compression index (Cc) is the slope of the linear portion of the pressure–void ratio curve on a semi-log plot, with pressure on the log scale (IS: 8009 – Part 1, 1976).
• This is a dimensionless parameter.
• For any two points on the linear portion of the plot-

${C_c} = \frac{{{e_o} - {e_1}}}{{\log \left( {\frac{{{p_1}}}{{{p_o}}}} \right)}}$

Where

po and p1 are pressures corresponding to e0  and e1  respectively