Question

The coefficient of permeability depends upon :
A. Void ratio of the soil
B. Duration of flow
C. Equivalent diameter of the soil grains
Choose the correct answer from the options given below :

• A. B and C only
• B. A and B only
• C. B only
• D. A and C only

Hint:

Other factors affecting permeability include the viscosity and unit weight of the fluid ($k \propto \gamma_w/\mu$), temperature (which affects viscosity), and the soil's degree of saturation.

Answer 1

The Correct Option is D

Concept: Permeability ($k$) is the ease with which water flows through soil. According to the Kozeny-Carman equation, $k$ is a function of the soil's physical structure and the fluid's properties.

Step 1: Evaluate Void Ratio (A).
Permeability is directly related to the void ratio ($e$). Larger voids allow for faster water movement. The relationship is often expressed as $k \propto e^3/(1+e)$. Thus, (A) is correct.

Step 2: Evaluate Duration of Flow (B).
Permeability is an inherent property of the soil and the fluid. While the *volume* of water collected depends on the duration of flow ($Q = kiAt$), the *coefficient* $k$ itself remains constant regardless of how long the water flows. Thus, (B) is incorrect.

Step 3: Evaluate Grain Diameter (C).
According to Allen Hazen's formula, $k = C (D_{10})^2$, where $D_{10}$ is the effective grain size. Larger particles create larger pores, significantly increasing permeability. Thus, (C) is correct.