Stability of Slopes MCQ with answer and solution

Concept

Geotechnical mechanisms of base failure in finite slopes

Formula

N_s = c / (γ × H)

Step-by-step solution

1. Slope failures in finite embankments are categorized as slope/face failure, toe failure, or base failure. 2. When the soil below the toe level is significantly softer and weaker than the embankment soil, the slip circle dips deep into the foundation soil. 3. The failure arc passes beneath the toe, manifesting as a base failure. 4. Hence, base failure occurs when soil below the toe is soft and weak. Answer: B

Explanation

In the stability analysis of finite slopes, a base failure occurs when the slip circle passes below the toe of the slope into the underlying foundation stratum. This type of failure typically occurs when the soil layer beneath the toe is soft, weak, or highly compressible relative to the slope material.

Why the other options are wrong

A) Strong soil below the toe forces the slip circle to exit at or above the toe (toe or slope failure). C) Steep slopes with high friction angles typically undergo face failures. D) Purely frictional soils fail via shallow surface ravelling/planar sliding.

Shortcut

Weak stratum below toe = Base failure; Firm stratum at toe = Toe failure.

Common mistake

Assuming steep slopes produce base failure (steep slopes typically produce face or toe failures).