DHARM252 GEOTECHNICAL ENGINEERING
7.28. A saturated clay layer 4 m thick is located 6 m below GL. The void ratio of the clay is 1.0. When
a raft foundation is located at 2 m below GL, the stresses at the top and bottom of the clay layer
increased by 150 and 100 kN/m^2 respectively. Estimate the consolidation settlement if the coef-
ficient of compressibility 0.002 cm^2 /N. (S.V.U.—B.Tech., (Part-time)—May, 1983)
7.29. In a consolidation test the following data was obtained:
Void ratio of the soil = 0.75
Specific gravity of the soil = 2.62
Compression Index = 0.1
Determine the settlement of a footing resting on the saturated soil with properties as given
above. The thickness of the compressible soil is 3 m. The increase in pressure at the centre of the
layer is 60 kN/m^2. The preconsolidation pressure is 50 kN/m^2.
If the coefficient of consolidation is 2 × 10–7 m^2 /s, determine the time in days for 90% consolida-
tion. Assume one-way drainage. (S.V.U.—B.Tech., (Part-time)—Apr. 1982)
7.30. A clay layer 5 m thick has double drainage. It was consolidated under a load of 127.5 kN/m^2. The
load is increased to 197.5 kN/m^2. The coefficient of volume compressibility is 5.79 × 10–4 m^2 /kN
and value of k = 1.6 × 10–8 m/min. Find total settlement and settlement at 50% consolidation. If
the test sample is 2 cm thick and attains 100% consolidation in 24 hours, what is the time taken
for 100% consolidation in the actual layer? (S.V.U.—Four year B.Tech.,—June, 1982)
7.31. The thickness of a saturated specimen of clay under a consolidation pressure of 100 kN/m^2 of is
24 mm and its water content is 20%. On increase of the consolidation pressure to 200 kN/m^2 , the
specimen thickness decreases by 3 mm. Determine the compression index for the soil if the
specific gravity of the soil grains is 2.70. (S.V.U.—B.Tech., (Part-time)—Sept., 1983)
7.32. If a representative clay specimen 20 mm thick, under double drainage, took 121 minutes for 90%
primary compression, estimate the time required for 50% primary compression of a field layer
2 m thick, bounded by impervious boundary at the bottom and sand at the top.
(S.V.U.—B.Tech., (Part-time)—Sept., 1983)
7.33. A bed of sand 12 m thick is underlain by a compressible stratum of normally loaded clay, 6 m
thick. The water table is at a depth of 5 m below the ground level. The bulk densities of sand
above and below the water table are 17.5 kN/m^3 and 20.5 kN/m^3 respectively. The clay has a
natural water content of 40% and LL of 45%. G = 2.75. Estimate the probable final settlement if
the average increment in pressure due to a footing is 100 kN/m^2.
(S.V.U.—B.E. (Part-time)—Apr., 1982)