Effective Stress Concept – Meaning of Neutral Stress in Soils In a saturated soil mass, the term 'neutral stress' refers to which quantity?

Introduction / Context:
The effective stress principle (σ′ = σ − u) is fundamental in soil mechanics. It separates total stress σ into effective stress σ′ carried by the soil skeleton and neutral stress u carried by the pore water. Many soil behaviors—strength, compressibility, and volume change—depend primarily on σ′, not on σ alone.

Given Data / Assumptions:

• Saturated soil; static conditions.
• Pore-water pressure u is well-defined.
• Neutral stress is a commonly used synonym in classical texts.

Concept / Approach:

Neutral stress is another name for pore-water pressure u. It acts equally in all directions within the water phase and does not contribute to shear resistance of the soil skeleton. The soil solids carry the effective stress. Understanding the split between u and σ′ is vital for predicting consolidation, shear strength, and stability under changing groundwater conditions.

Step-by-Step Solution:

Verification / Alternative check:

Field measurements using piezometers directly read u, confirming it is distinct from the stress carried by the soil skeleton read indirectly through deformation and strength.

Why Other Options Are Wrong:

(a) and (b) are not standard definitions; (d) describes effective stress, not neutral stress.

Common Pitfalls:

Assuming total stress controls strength; ignoring changes in u during rapid loading or drawdown.

Final Answer:

Stress taken up by the pore water (pore-water pressure)