Consolidation MCQ with answer and solution

Concept

Compression index and primary consolidation settlement

Formula

S_c = [Cc × H0 / (1 + e0)] × log10(σ₁' / σ₀')

Step-by-step solution

1. The compression index (Cc) is the slope of the linear virgin consolidation curve on an e vs log(σ') plot. 2. Primary consolidation settlement for normally consolidated clay is Sc = [Cc × H0 / (1 + e0)] × log10(σ₁' / σ₀'). 3. Hence, Cc directly enables calculation of the total primary consolidation settlement. 4. Rate of settlement is governed by the coefficient of consolidation (cv), not Cc. Answer: A

Explanation

Compression index (Cc) represents the slope of the linear portion of the void ratio versus logarithm of effective stress (e - log σ') curve from an oedometer consolidation test. It is directly used to calculate the primary consolidation settlement (total settlement) of normally consolidated clayey soils.

Why the other options are wrong

B) Rate of settlement is determined by the coefficient of consolidation cv and time factor Tv. C) Initial settlement is elastic settlement governed by elastic modulus Eu. D) Pre-consolidation pressure is determined from Casagrande's graphical construction.

Shortcut

Compression Index (Cc) = Total settlement; Coefficient of Consolidation (cv) = Rate of settlement.

Common mistake

Confusing Cc (governs magnitude of settlement) with cv (governs time rate of settlement).