According to the effective stress principle in soil mechanics, consolidation of saturated soils primarily depends on which stress quantity?

Introduction / Context:
Consolidation is the time-dependent compression of saturated fine-grained soils due to expulsion of pore water under sustained loading. Terzaghi’s effective stress principle is foundational: soil skeleton deformation—and thus long-term settlement—depends on effective stress, not total stress alone.

Given Data / Assumptions:

• Saturated soil under load; drainage allowed over time.
• Total stress σ, pore water pressure u, effective stress σ′ where σ′ = σ − u.
• Primary interest: what stress governs consolidation magnitude.

Concept / Approach:

When load is applied, total stress rises instantly, but pore pressure initially carries part or all of the increment (undrained). With time, water drains, pore pressure dissipates, and effective stress increases. Settlement occurs as the soil skeleton takes more load. Therefore, final consolidation settlement correlates with change in effective stress and compressibility (Cc, mv), not directly with total stress or pore pressure alone.

Step-by-Step Solution:

Verification / Alternative check:

Laboratory oedometer tests interpret settlement using effective stress changes and the e–log p relationship, confirming σ′ control. Different drainage boundaries change the rate (Cv), not the governing stress measure for magnitude.

Why Other Options Are Wrong:

• “Does not depend on the present stress”: False; stress level and history (preconsolidation) are critical.
• “Function of pore water pressure” alone: Only transiently; long-term settlement ties to σ′.
• Total stress alone ignores pore pressure.
• Independence from drainage is incorrect; drainage controls time rate (but not the governing stress definition).

Common Pitfalls:

• Confusing immediate (elastic) settlement with consolidation.
• Ignoring preconsolidation pressure which alters compressibility.

Final Answer:

is a function of the effective stress