Permeability Test for Granular Soils (Constant-Head Method) - Soil Properties: Testing, Measurement, and Evaluation - page 251

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CHAPTER EIGHTEEN

CHAPTER EIGHTEEN

Permeability Test
for Granular Soils
(Constant-Head
Method)

Permeability Test
for Granular Soils
(Constant-Head
Method)

(Referenced Document: ASTM D 2434)

Permeability refers to the propensity of a material to allow fluid to move
through its pores or interstices. In the context of soil, permeability gen-
erally relates to the propensity of a soil to allow water to move through
its void spaces. According to Darcy's law, the flow rate of water q through
a soil of cross-sectional area A is directly proportional to the imposed
gradient (slope) i ,or

INTRODUCTION

q
A ~ i

(18-1)

If a constant of proportionality k is introduced, we obtain the equation

(18-2)

q kiA

The constant k is known as the coefficient of permeability, or just per-
meability. Obviously, it indicates the ease with which water will flow
through a given soil. The greater the value of permeability, the greater
the flow will be for a given area and gradient.
Permeability is an important soil parameter for any project where
flow of water through soil is a matter of concern—for example, seepage
through or under a dam and drainage from subgrades or backfills.

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