Mohr–Coulomb Framework – Factors Influencing Shear Strength of Soils Which statements about soil shear strength are generally correct under the Mohr–Coulomb concept and basic observations?

Introduction / Context:
Soil shear strength governs stability in slopes, retaining structures, and foundations. The Mohr–Coulomb model provides a convenient linear envelope relating shear stress at failure to normal stress through cohesion and friction parameters that capture bonding and interparticle resistance mechanisms.

Given Data / Assumptions:

• Shear strength criterion: τ_f = c + σ′ * tan(φ).
• Effective stress framework for drained conditions; analogous total stress form for undrained clays.
• Parameters c and φ determined by appropriate shear tests.

Concept / Approach:

According to τ_f = c + σ′ * tan(φ), increasing normal effective stress raises shear strength (statement a). At σ′ = 0, shear strength equals c, hence proportionality to cohesion (statement b). In practice, “soil strength” often implies shear strength because most failures are shear governed (statement c). The frictional contribution grows with tan(φ), confirming statement d. Therefore, all statements collectively describe how shear strength varies with stress and soil parameters.

Step-by-Step Solution:

Verification / Alternative check:

Direct shear and triaxial test results across confining stresses display linear or near-linear envelopes supporting the Mohr–Coulomb relation in many soils.

Why Other Options Are Wrong:

Since (a)–(d) are all valid general statements, any single choice would be incomplete; only “All of the above” is comprehensive.

Common Pitfalls:

Confusing total and effective stress parameters; assuming c is a true “cohesion” for sands—it is usually taken as zero in drained analyses.

Final Answer:

All of the above