The Coefficient of Permeability of Soil by Constant Head Permeameter
This test is suitable for coarse-grained soils which are highly permeable. The apparatus used for this test is called a constant head permeameter. Fig (a,b) shows the diagrammatic representation of this test.
The sample of length ‘L’ & cross-sectional area ‘A’ is subjected to a head ‘h’ which is kept constant (by overflows) during the progress of the test.
The test is performed by allowing the flow of water through the sample and measuring the quantity of discharge (Q) in time ‘t’ with the help of a measuring jar.
The value of the coefficient of permeability (K) can be computed directly from Darcy’s law. We have from Darcy’s law, Discharge per unit time-
(q) = Q/t = K.i.A
Or, K = Q/t.i.A
Or, K = QL/A.h.t
[where, i (Hydraulic gradient) =h/L]