Components of shear resistance in soils: Which mechanisms fundamentally constitute the shear resistance of a soil mass under loading?

Introduction / Context:
Shear resistance governs slope stability, bearing capacity, and lateral earth pressures. The Mohr–Coulomb strength criterion captures the combined effects of friction and cohesion, which arise from several micro-mechanical mechanisms in granular and fine-grained soils.

Given Data / Assumptions:

• Soil is a particulate medium with contacts and pore water.
• Loading induces relative particle motions and fabric changes.
• No special cementation beyond typical natural bonds unless stated.

Concept / Approach:

Soil shear strength comprises: (1) interparticle friction at contacts, mobilized when particles slide; (2) structural interlocking, where angular particles resist rearrangement; and (3) cohesion/adhesion due to electrochemical attractions, cementation, or suction in fine-grained or partially saturated soils. These combine to produce observable shear strength parameters c and φ used in design.

Step-by-Step Solution:

Verification / Alternative check:

Laboratory tests (direct shear, triaxial) show frictional envelopes with intercepts when bonding/suction exists, confirming all mechanisms contribute.

Why Other Options Are Wrong:

Since each listed mechanism is real, “All the above” is correct; “None” is inappropriate.

Common Pitfalls:

Assuming cohesion only exists in clays; neglecting suction-induced apparent cohesion in partially saturated sands.

Final Answer:

All the above