Question Bank • QB_SWCE_ADV_112 NAT • 1 Mark

Section 4: Soil and Water Conservation Engineering

Soil Mechanics

Subtopic: Index properties of soils

Question Statement:

A clayey soil has a liquid limit $w_L = 52\%$, plastic limit $w_P = 24\%$, and the percentage of soil particles finer than $2\,\mu\text{m}$ is $35\%$. The activity of the clay ($A$) is ________ (round off to two decimal places).

Answer Key:

0.80

Step-by-Step Solution & Explanation

1. Plasticity index ($I_p$): $I_p = w_L - w_P = 52\% - 24\% = 28\%$ 2. Activity of clay ($A$) defined by Skempton: $A = \frac{I_p}{\% \text{ clay-sized fraction } (< 2\,\mu\text{m})}$ $A = \frac{28}{35} = 0.80$ (Classified as normal clay, since $0.75 \le A \le 1.25$).
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