DHARM164 GEOTECHNICAL ENGINEERING
5.18 (a) State the important factors that affect the permeability of a soil.
(b) A permeameter of 8.2 cm diameter contains a sample of soil of length 35 cm. It can be used
either for constant head or falling head tests. The standpipe used for the latter has a diameter
of 2.5 cm. In the constant head test the loss of head was 116 cm measured on a length of 25
cm when the rate of flow was 2.73 ml/s. Find the coefficient of permeability of the soil.
If a falling head test were then made on the same soil, how much time would be taken for the
head to fall from 150 to 100 cm? (S.V.U.—B.E., (N.R.)—March, 1966)
5.19 The initial head is 300 mm in a falling head permeability test. It drops by 10 mm in 3 minutes.
How much longer should the test continue, if the head is to drop to 180 mm?
5.20 Determine the average horizontal and vertical permeabilities of a soil mass made up of three
horizontal strata, each 1 m thick, if the coefficients of permeability are 1 × 10–1 mm/s, 3 × 10–1
mm/s, and 8 × 10–2 mm/s for the three layers.
5.21. The coefficient of permeability of a soil sample is found to be 9 × 10–2 mm/s at a void ratio of 0.45.
Estimate its permeability at a void ratio of 0.63.
5.22 In a falling head permeability test the time intervals noted for the head to fall from h 1 to h 2 and
from h 2 to h 3 have been found to be equal. Show the h 2 is the geometric mean of h 1 and h 3.
5.23 A sand deposit of 12 m thick overlies a clay layer. The water table is 3 m below the ground
surface. In a field permeability pump-out test, the water is pumped out at a rate of 540 litres per
minute when steady state conditions are reached. Two observation wells are located at 18 m and
36 m from the centre of the test well. The depths of the drawdown curve are 1.8 m and 1.5 m
respectively for these two wells. Determine the coefficient of permeability.
5.24 The following data relate to a pump-out test:
Diameter of well = 24 cm
Thickness of confined aquifer = 27 m
Radius of circle of influence = 333 m
Draw down during the test = 4.5 m
Discharge = 0.9 m^3 /s.
What is the permeability of the aquifer?
5.25 (a) Why is the capillary rise greater for fine grained soils than for coarse-grained soils?
(b) What is the effect of temperature of the capillary rise of water in soil?
(c) How is capillarity related to the firm condition of fine-grained soils’ near surface?
(d) How can the effects of capillarity be removed from a soil?
5.26 A glass tube of 0.02 mm diameter. What is the height to which water will rise in this tube by
capillarity action? What is the pressure just under the meniscus?
5.27 The effective size of a soil is 0.05 mm. Assuming the average void size to be (1/5) D 10 , determine
the capillary rise of pore water in this soil.
5.28 The effective size of a silt soil is 0.01 mm. The void ratio is 0.72. What is the height of capillary
rise of water in this soil?
5.29 The effective sizes of two sands are 0.09 mm and 0.54 mm. The capillary rise of water in the first
sand is 480 mm. What is the capillary rise in the second sand, if the void ratio is the same for
both sands?
5.30 The water table is lowered from a depth of 3 m to a depth of 6 m in a deposit of silt. The silt
remains saturated even after the water table is lowered. What would be the increase in the
effective stress at a depth of 3 m and at 10 m on account of lowering of the water table? Assume
the water content as 27% and grain specific gravity 2.67.