Question

A falling head permeability test was performed on a re-moulded silty clay soil sample 150 mm in diameter and 250 mm in length. The diameter of the standpipe was 12.7 mm. At the start of the test, the height of the water in the standpipe measured 2,236 mm above the constant water level where the soil sample was immersed in. After 7 hours and 45 minutes, the height of the water in the standpipe was measured at 1971 mm. Determine: (i) the coefficient of permeability of the soil (in m/sec), and (ii) the estimated height of the water in the standpipe after a further 12 hours of running this test. (iii) the total time (from the start of the test in days, hours, minutes and seconds) it will take for the water level in the standpipe to reach a height of 600 mm.  

Answer 1

1.Coefficient of permeability k =

a= area of cross section of stand pipe =3.14*d²/4

a =3.14*12.7²/4=126.67mm2

A= area of sample=3.14*d²/4

A=3.14*150²/4=17671.46 mm2

L=length of sample=250mm=0.25m

T time requires=7 hours 45 minutes=27900sec

h1= initial height

h1= initial height=2236mm

h2= final height=1971mm

Coefficient of permeability K=8.09*10^-9m/s

2. When time increases by 12 hour

New time ,t=7hour45min+12hour

t=19hour 45 min

t=71100seconds

h2= final height=1621.5mm

3. when h2= 600mm

When water height fall to 600mm time t=291072sec

t=80hours 51min 12 sec

When water height fall to 600mm time t=3day 8 hour 51min 12sec