Section 4: Soil and Water Conservation Engineering
Soil Mechanics
Subtopic: Engineering properties of soils
Question Statement:
The mass of a 3.0 mm crumbled soil thread is 17.5×10⁻³ kg. On oven-drying, the mass reduces to 14.9×10⁻³ kg. The liquid limit of the soil sample is 35.4%. The plasticity index of the soil sample is
Options:
(A) 14.9
(B) 18.0
(C) 32.8
(D) 35.4
Official Answer Key:
B
Step-by-Step Solution & Explanation
The 3 mm crumbling thread is the classical Atterberg plastic limit (PL) test: PL(%) = (mass water/mass dry) ×100 = (17.5−14.9)/14.9 × 100 = 17.45%. Plasticity Index PI = LL − PL = 35.4 − 17.45 = 17.95 ≈ 18.0%.
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