Section 4: Soil and Water Conservation Engineering
Soil Mechanics
Subtopic: Shear strength
Question Statement:
In a consolidated undrained (CU) triaxial compression test on a normally consolidated saturated clay with pore pressure measurement, the effective cohesion intercept ($c'$) and the failure envelope are characterized by:
Options:
(A) $c' = 0$, and the effective stress failure envelope passes through the origin with effective friction angle $\phi'$
(B) $c' > 0$ and $\phi' = 0$
(C) Both $c'$ and $\phi'$ equal zero under all strain rates
(D) The effective stress path is always vertical and independent of deviator stress
Answer Key:
A
Step-by-Step Solution & Explanation
For normally consolidated clays, there is no pre-consolidation stress memory; hence, the effective cohesion intercept $c' = 0$. The Mohr-Coulomb failure envelope in terms of effective stresses passes directly through the origin: $\tau_f = \sigma' \tan\phi'$. Option A is correct.