## Review And Exercise Of The Soil Mechanics

In a falling head permeameter test on a fine sand the sample had a diameter of 76 mm and a length of 152 mm with a stand-pipe of 12.7 mm diameter. A stop watch was started when h was 508 mm and read 19.6 s when h was 254 mm; the test was repeated for a drop from 254 mm to 127 mm and the time was 19.4 s. Determine an average value for k in m/s.

Answer 1.5 x 10~4m/s EXERCISE 2.2

A sample of coarse sand 150 mm high and 55 mm in diameter was tested in a constant head permeameter. Water percolated through the soil under a head of 400 mm for 6.0 s and the discharge water had a mass of 400 g. Determine k in m/s.

Answer 1.05 x 10~2m/s EXERCISE 2.3

In order to determine the average permeability of a bed of sand 12.5 m thick overlying an impermeable stratum, a well was sunk through the sand and a pumping test carried out. After some time the discharge was 850kg/min and the drawdowns in observation wells 15.2m and 30.4m from the pump were 1.625 m and 1.360 m respectively. If the original water table was at a depth of 1.95 m below ground level, find the permeability of the sand (in m/s) and an approximate value for the effective grain size.

Answer k = 6.7 x 10~4m/s, Di0 = 0.26mm EXERCISE 2.4

A cylinder of cross-sectional area 2500 mm2 is filled with sand of permeability 5.0mm/s. Water is caused to flow through sand under a constant head using the arrangement shown in Fig. 2.34.

250 mm

250 mm

100 mm

20 mm

100 mm

20 mm

Determine the quantity of water discharged in lOmin. Answer 9 x 106mm3

0 0