A constant head permability test is performed on a soil that is 2 cm X 2 cm squa

Question

A constant head permability test is performed on a soil that is 2 cm X 2 cm square and 2.5 cm long. The head difference applied during the test is 18 cm, and 5 cm^3 is collected over a time of 100 sec.

(a) compute the permability based on these conditions and results.

I found the answer to be k = .0017 cm/sec

i need help with

(b) a falling head permability test is to be done on the same soil specimen in the same time, and the standpipe diamter is .8 cm. if the average head during the test should be 18 cm, what are h1 and h2?

Explanation / Answer

k = V L/ A hT

k = 5 *2.5/(4*18*100)

k = 1.736*10^-3 cm/sec

(b)

k = [aL/At] * ln(h2/h1)

a = 3.14*0.8^2/4 = 0.5024 cm^2

now,

1.736*10^-3 = (.5024*2.5/(4*100))* ln(h2/h1)

ln(h2/h1) = 0.552866

h2/h1 = 1.738

Average head =18 = (h2 +h1)/2

h1 + h2 = 36

h2/h1 = 1.738

solving the above two,

we get ,

h2 = 22.8517 cm

h1 = 13.1483 cm

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