Shear strength of cohesionless soils (sand): dominant influencing factor For a dense, cohesionless soil (c ≈ 0), which listed factor most directly governs its shearing strength under drained loading?

Introduction / Context:
Cohesionless soils such as sands mobilize shear resistance primarily through friction and interlocking. Understanding what truly controls their shear strength is fundamental for foundation bearing capacity, lateral earth pressure, and slope stability analyses in drained conditions.

Given Data / Assumptions:

• C ≈ 0; strength arises from friction angle φ and normal effective stress σ′.
• Drained loading is considered; pore pressure dissipation occurs.
• Dilatancy can modify peak strength but still scales with σ′.

Concept / Approach:

Mohr–Coulomb for cohesionless soils: τ = σ′ * tan φ. The mobilized shear resistance is directly proportional to the effective normal stress on the plane. While density affects φ_peak via dilatancy and fabric, the most immediate variable in the strength expression is σ′ (confining pressure).

Step-by-Step Solution:

Verification / Alternative check:

Triaxial/drained direct shear tests show higher σ′ produces proportionally higher peak shear stresses for a fixed φ.

Why Other Options Are Wrong:

Dry density influences φ but indirectly; rate of loading affects drainage in clays rather than drained sand strength; “nature of loading only” is incomplete; color is irrelevant.

Common Pitfalls:

Confusing density effects (on φ) with the governing role of σ′; applying undrained logic from clays to sands.

Final Answer:

Confining (normal effective) pressure