Coefficient of soil permeability:

The results of a constant head permeability test of a fine sand are as follows: area of the soil sample 180sqcm, length of the specimen 32cm, constant head maintained 46cm, flow of water through the specimen 200ml in 5 minutes. Determine the coefficient of permeability in cm/s

Solution

Coefficient of soil permeability

NOTE

The coefficient of permeability k is a measure  of the rate of flow of water through saturated  soil under a given hydraulic gradient i, cm/cm,  and is defined in accordance with Darcy’s law  as:

Assumption: Flow is laminar

When the flow through soil is laminar, Darcy’s law (Darcy, 1856)  applies:

Darcy’s law states that for laminar flow the velocity of flow, V is proportional to the hydraulic gradient i.

V=Ki  (k is the constant of proportionality)

q =  v . A = k i A

Where q = rate of flow, cm3/s.  A = cross-sectional area of soil conveying flow, cm2

The rate of flow under laminar flow conditions through a  unit cross-sectional are of the porous medium under a unit  hydraulic gradient is defined as the ]coefficient of permeability.

Permeability in soil  mechanics is a measure of how easily a fluid (water) can flow  through a porous medium (soil).

The flow of water through soils, called seepage, occurs when  there is a difference in the water level (energy) on the two sides of  a structure such as a dam or a sheet pile.