Stress–Deformation Trends Under Changing Effective Stress Which statement correctly describes how key soil indices respond when effective stress increases (loading) in a typical compressible soil?

Introduction / Context:
Understanding qualitative trends under changes in effective stress is vital for consolidation, settlement prediction, and permeability assessment. As soils are loaded, their structure compresses, affecting void ratio, hydraulic conductivity, and compressibility parameters in predictable ways for most natural soils.

Given Data / Assumptions:

• Normal consolidation or general compressible behavior (not cemented rock-like materials).
• Drainage permitted over time so that effective stress increases.
• Comparisons are qualitative trends with increasing effective stress.

Concept / Approach:

With increasing effective stress, soil particles pack more closely, so void ratio e decreases. Reduced void space typically leads to decreased permeability k. The coefficient of volume change m_v, which relates volumetric strain to stress increment, generally decreases as stress level grows (soil stiffens). Therefore the only universally correct statement among the options is that void ratio decreases as effective stress increases.

Step-by-Step Solution:

Verification / Alternative check:

e–log σ′ curves and k–e relationships measured in oedometer tests show these monotonic trends for most clays and silts.

Why Other Options Are Wrong:

(b), (c), and (d) contradict typical observed behavior; permeability and compressibility do not increase with increasing effective stress.

Common Pitfalls:

Confusing immediate total-stress changes with long-term effective-stress changes; extrapolating trends outside the tested stress range.

Final Answer:

When effective stress increases, void ratio decreases