Question Bank • QB_SWCE_ADV_102 MCQ • 1 Mark

Section 4: Soil and Water Conservation Engineering

Soil Mechanics

Subtopic: Index properties of soils

Question Statement:

For a cohesive clay soil, if the natural moisture content $w$ equals its plastic limit $w_P$, the liquidity index ($I_L$) and consistency index ($I_c$) are respectively:

Options:

  • (A) $I_L = 0$ and $I_c = 1$
  • (B) $I_L = 1$ and $I_c = 0$
  • (C) $I_L = 0.5$ and $I_c = 0.5$
  • (D) $I_L = -1$ and $I_c = 1$

Answer Key:

A

Step-by-Step Solution & Explanation

Definitions: 1. Plasticity index: $I_p = w_L - w_P$. 2. Liquidity index: $I_L = \frac{w - w_P}{I_p}$. When $w = w_P$, $I_L = \frac{0}{I_p} = 0$. 3. Consistency index: $I_c = \frac{w_L - w}{I_p}$. When $w = w_P$, $I_c = \frac{w_L - w_P}{I_p} = \frac{I_p}{I_p} = 1$. 4. Notice $I_L + I_c = 1$ always holds. Option A is correct.
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