Shear strength parameter ranges: What is the usual range of the angle of internal friction (φ) for clays under typical conditions?

Introduction / Context:
The friction angle φ reflects the frictional component of shear strength. In clays, undrained shear strength is governed primarily by cohesion (apparent) with very low friction angle, whereas effective-stress friction angles for OC clays can be higher under drained conditions. The “usual” small φ is commonly referenced for clays in simple discussions.

Given Data / Assumptions:

• Typical natural clays in undrained short-term conditions.
• No cementation or unusual structure.

Concept / Approach:
For saturated clays tested undrained (UU), φ_u is near zero, leading to total-stress analyses that use undrained shear strength cu. Under long-term drained conditions, especially for overconsolidated clays, effective φ′ may range higher (20–30°), but “usually” for quick characterization of clays, φ close to zero is cited.

Step-by-Step Solution:

Verification / Alternative check:
UU triaxial tests on saturated clays often yield φ_u ≈ 0°. Effective-stress tests (CD/CU) yield larger φ′ but that is a different context.

Why Other Options Are Wrong:

• Higher ranges correspond to sands or drained OC clays, not the usual undrained characterization of clays.

Common Pitfalls:
Failing to distinguish total vs effective stress parameters; applying sand φ values to clays.

Final Answer:
0° to 5°