DHARMSOIL MOISTURE–PERMEABILITY AND CAPILLARITY 163
5.6 What are the various parameters that effect the permeability of soil in the field? Critically
discuss. (S.V.U.—B.Tech., (Part-time)—April, 1982)
5.7 What are the various factors that affect the permeability of a soil stratum? If k 1 , k 2 , k 3 are the
permeabilities of layers h 1 , h 2 , h 3 thick, what is its equivalent permeability in the horizontal and
vertical directions? Derive the formulae used. (S.V.U.—Four-year B.Tech.,—June, 1982)
5.8 Differentiate between ‘Constant Head type’ and ‘Variable Head type’ permeameters. Are both of
them required in the laboratory? If so, why? Derive the expression for the coefficient of perme-
ability as obtained from the variable head permeameter.
(S.V.U.—B.Tech., (Part-Time)—June, 1981)
5.9 Estimate the coefficient of permeability for a uniform sand with D 10 = 0.18 mm.
5.10 Explain the significance of permeability of soils. What is Darcy’s law? Explain how the perme-
ability of a soil is affected by various factors. (S.V.U.—B.R., (R.R.)—Feb., 1976)
5.11 Distinguish between superficial velocity and seepage velocity. Describe briefly how they are
determined for sand and clay in the laboratory. (S.V.U.—B.E., (R.R.)—Nov., 1974)
5.12 List the factors that affect the permeability of a given soil. State the precautions that should be
taken so that satisfactory permeability data may be obtained.
Explaining the test details of a falling head permeameter, derive the formula used in the compu-
tation. Also evaluate the types of soil material for which falling head and variable head
permeameters are used in the laboratory. Compare the relative merits and demerits of labora-
tory and field methods of determining the coefficient of permeability.
(S.V.U.—B.E., (R.R.)—Nov., 1973)
5.13 Calculate the coefficient of permeability of a soil sample, 6 cm in height and 50 cm^2 in cross-
sectional area, if a quantity of water equal to 430 ml passed down in 10 minutes, under an
effective constant head of 40 cm. (S.V.U.—B.E., (R.R.)—Dec., 1971)
5.14 Define coefficient of permeability and list four factors on which the permeability depends.
A falling head permeability test is to be performed on a soil sample whose permeability is esti-
mated to be about 3 × 10–5 cm/s. What diameter of the standpipe should be used if the head is to
drop from 27.5 cm to 20.0 cm in 5 minutes and if the cross-sectional area and length of the
sample are respectively 15 cm^2 and 8.5 cm? Will it take the same time for the head to drop from
37.7 cm to 30.0 cm? (S.V.U.—B.E., (R.R.)—Nov., 1973)
5.15 (a) What are the conditions necessary for Darcy’s law to be applicable for flow of water through
soil?
(b) Why is the permeability of a clay soil with flocculated structure greater than that for it in the
remoulded state?
5.16 (a) State the principle of Darcy’s law for laminar flow of water through saturated soil.
(b) Demonstrate that the coefficient of permeability has the dimension of velocity.
(c) The discharge of water collected from a constant head permeameter in a period of 15 minutes
is 400 ml. The internal diameter of the permeameter is 6 cm and the measured difference in
heads between the two gauging points 15 cm apart is 40 cm. Calculate the coefficient of
permeability and comment on the type of soil. (S.V.U.—B.E., (N.R.)—Sept., 1967)
5.17 A glass cylinder 5 cm internal diameter with a screen at the bottom is used as a falling head
permeameter. The thickness of the sample is 10 cm. The water level in the tube at the start of
the test was 40 cm above tail water level and it dropped by 10 cm in one minute while the level
of tail water remained unchanged. Determine the value of the coefficient of permeability.
(S.V.U.—B.E., (N.R.)—Sep., 1968)