Shear Strength MCQ with answer and solution

Concept

Shear strength parameters of clays under different drainage conditions and stress histories.

Formula

τ = c + σ tan(φ)

Step-by-step solution

1. Analyze Statement 1: Normally consolidated clays have no pre-consolidation pressure history, hence their effective cohesion intercept is zero, making the effective stress failure envelope pass through the origin. 2. Analyze Statement 2: In a UU test on saturated clay, pore water pressure develops without allowing drainage. The shear strength is independent of the total confining pressure, resulting in a horizontal total stress failure envelope (φ_u = 0). 3. Conclude that both statements are correct.

Explanation

Statement 1 is correct because for a normally consolidated clay, the effective stress failure envelope passes through the origin (cohesion intercept c' = 0). Statement 2 is correct because in an unconsolidated-undrained (UU) test on a saturated clay, the total stress failure envelope is horizontal (angle of shearing resistance φ_u = 0) because the shear strength remains constant regardless of the confining pressure.

Why the other options are wrong

A: Statement 2 is also correct. B: Statement 1 is also correct. D: Both statements are correct.

Shortcut

Remember: Normally consolidated clay -> c'=0 (passes through origin). UU test on saturated clay -> φ_u=0 (horizontal envelope).

Common mistake

Confusing effective stress parameters with total stress parameters, or confusing normally consolidated clay with over-consolidated clay.