GATE 2017 CE (CE1) – Question 46

Geotechnical Engineering · Three-phase system, phase relationships, index properties and soil classification · 2 marks · Multiple choice

A soil has natural moisture content 18%, liquid limit 60%, plastic limit 25% and clay-sized fraction 25%. Its liquidity index and Skempton activity, respectively, are

−0.2 and 1.4
0.2 and 1.4
−1.2 and 0.714
1.2 and 0.714

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Correct answer: (A) −0.2 and 1.4

Explanation

The plasticity index is $I_P=w_L-w_P=60-25=35\%$. Liquidity index is $(w-w_P)/I_P=(18-25)/35=-0.2$, consistent with moisture below the plastic limit. Activity is plasticity index divided by percentage clay fraction, $35/25=1.4$. Thus A.

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