Laboratory methods to determine Coefficient of permeability is/are 

Explanation:

Lab test to determine permeability:

1. Constant head permeability test:

The coefficient of permeability for coarse-grained soil is determined by means of Constant-head permeability test. The degree of saturation of soil should be 100%.

By Darcy’s Law,

Q = k i A

\(Q = k\dfrac{h}{L}A\)

\(k = \dfrac{{QL}}{{Ah}}\)

where, q = Discharge collected in time ‘t’, L = Distance between manometer taping points, A = Cross-sectional area of the sample, H = Difference in manometer levels i.e the head loss.

2. Variable head permeability test:

the falling head permeability test is used for relatively less permeable soils (fine-grained) where the discharge is small.

So here in clayey soil falling head permeability test can be used.

For falling head permeability test

\(K = \dfrac{a}{A}\dfrac{L}{t}\;\ln\left( {\dfrac{{{h_1}}}{{{h_2}}}} \right)\)

\({\rm{k}} = 2.303\dfrac{{\rm{a}}}{{\rm{A}}} \times \dfrac{{\rm{L}}}{{\rm{t}}}{{\rm{log}}_{10}}\left( {\dfrac{{{{\rm{h}}_1}}}{{{{\rm{h}}_2}}}} \right)\)

Where,

k = permeability, a = Area of tube in m2, A = Area of sample in m2, t = time in sec, L = length in m, h1 = Level of time t = 0, and h2 = Level of time t

Additional Information

Field test to determine permeability:

1. Pumping out test:

(i) The pumping out test is more general and accurate method for permeability determination below the water table.

(ii) This test is carried out for two basics flow conditions; unconfined flow (gravity flow) and confined flow (artesian flow).

2. Pumping in test:

(i) The pumping in test is suitable for low permeability and thin strata adequate yield may not be available for pumping out test.

(ii) By these test, permeability determination of soil at the bottom of the borehole is obtained. Hence these are best suited for permeability determination of stratified deposits.

There are basically two types of pumping test:

• Open-end test
• Packers test