2. (a) A soil sample 10 cm in diameter was subject to a constant

head permeability test. The total head was measured at two

points of the sample using manometers, one close to the top

and another close to the bottom of the sample (distance

between the points: 108 cm). The first manometer recorded a

head of 189 cm and the other 177 cm. The amount of water

collected in 1800 seconds was Q=2700 cm³. Calculate the

permeability of the soil.

(7

marks)

(b) A falling head permeability test was performed on a silt

sample of 100 mm in diameter and 300 mm in height. Two

different standpipe diameters were used. Measurements of

water level height h in each standpipe were taken at different

time intervals. The results of the test are shown in Table 2.

Calculate the permeability of the soil. (10 marks)

BEng Civil Engineering -Soil Mechanics-Referred /Deferred Coursework

Standpipe

diameter (mm)

9

12.5

3

Table 2

Water level in standpipe

Final level

Initial level

h₂ (mm)

h₂ (mm)

600

420

600

360

420

300

360

180

Time interval

At (s)

116

110

320

240

(c) If the voids ratio of a sandy soil is 0.75 and its specific gravity

G₁= 2.63, determine the critical hydraulic gradient of the soil.

(Take the unit weight of water yw = 10 kN/m³).

(3 marks)