OBJECT OF EXPERIMENT
The object of the experiment is to determine the coefficient of permeability of soil by variable head permeameter.
1. Permeameter tube consisting of stand pipes
4. Stop watch
The variable head permeameter consists of a metal mould in which soil samples can be compacted or undisturbed samples can be placed. Porous stones are fitted at the top and the bottom of the mould and it is kept in a constant level. The top is connected to a glass stand pipe of suitable size.
It can be proved on the basis of Darcy’s law for flow through soil that the coefficient of permeability.
K = 2.3 [aL/A(t1 – t0)] log10 (h0/h1)
where, a = Area of cross section of the stand pipe
L = Length of soil sample
A = Area of cross section of soil sample
h0 = Initial head of water
h1 = The head of water after a time t1
t0 = Initial time
t1 = Final time
1. Water is filled in the stand pipe which is being used. The stopcock at the top of the permeameter is closed after the expulsion of all the air from the rubber tube and the connecting pipe.
2. If the soil is not already saturated, it is left for about 24 hours for saturation till the trough is filled up to the top.
3. The stand pipe is filled with water, almost up to the top, after tightening the clamp on the rubber tube.
4. The clamp is released, when the water level in the stand pipe starts falling steadily, it is read and simultaneously the stop watch is started.
5. The flow of water is stopped when the water level in the stand pipe falls through a sufficient distance as indicated in the table and the time noted.
6. Five sets of such independent readings are taken and an average value of the coefficient of permeability, ‘K’ is found out.
OBSERVATIONS AND CALCULATIONS
Diameter of the stand pipe :
Area of cross section of stand pipe :
Area of cross section of sample :
Length of the sample :
|Initial Head (h0) (cm)||Final Head (h1) (cm)||Initial time (t0) (sec)||Final time (t1) (sec)||Time interval (sec)||Value of K (cm/sec)||
Average value of K
Coefficient of permeability of the given soil sample has been found to be ………………… cm/sec.