Darcy’s Law – Conditions for Validity in Seepage Through Soils Darcy’s law for laminar flow through porous media is applicable provided the soil and flow satisfy which conditions?

Introduction / Context:
Darcy’s law (q = k * i * A) is fundamental for analyzing seepage, filter design, and dewatering. However, it holds under specific conditions related to soil fabric and flow regime. Recognizing these ensures correct application and interpretation of permeability tests and flow nets.

Given Data / Assumptions:

• Steady, laminar flow through a saturated porous medium.
• Constant fluid properties over the domain.
• Representative elementary volume concept is valid.

Concept / Approach:

Darcy’s law presumes linear proportionality between seepage velocity and hydraulic gradient. This linearity is typically satisfied when the medium is homogeneous and isotropic at the scale of interest, and when the soil skeleton does not deform significantly (incompressible framework) under the hydraulic load. At high gradients in very coarse materials, non-Darcian (Forchheimer) behavior can arise.

Step-by-Step Solution:

Verification / Alternative check:

Laboratory constant-head and falling-head tests demonstrate linear head loss with discharge within laminar regime; deviations occur in gravels or cracked clays where assumptions fail.

Why Other Options Are Wrong:

Any single condition alone is insufficient; the combination in (d) is the safest practical statement. Option (e) contradicts established seepage theory.

Common Pitfalls:

Applying Darcy’s law to turbulent flows in rockfill or to anisotropic stratified clays without directional permeability corrections.

Final Answer:

All of the above