DHARM422 GEOTECHNICAL ENGINEERING
20
m
X120 m40 m40 mFig. 11.18 Plan of spoil heap (Prob. 11.8)
11.9 A boring indicates the existence of a 20-metre thick clay stratum above sand. The hydrostatic
pressure at the top of the clay layer is 60 kN/m^2. The pore pressure at the bottom of the clay layer
is reduced permanently by 60 kN/m^2 by pumping. If the void ratio of clay is reduced from 1.000
to 0.975 by pumping, estimate the ultimate settlement due to this.
11.10 A clay layer 25 metres thick has a saturated unit weight of 19.2 kN/m^2. Ground water level
occurs at a depth of 5 metres. It is proposed to construct a reinforced concrete foundation, 12.5 m
× 50 m, on top of the layer, to transmit a uniform pressure of 150 kN/m^2.
Determine the settlement at its centre, assuming that the void ratio drops from 0.725 to 0.700
due to loading. E for the clay is 30 MN/m^2.
11.11 The loading period for a building extended from Aug., 1962 to Aug., 1965. The average settle-
ment was found to be 100 mm in Aug., 1968. The ultimate settlement was expected to be
300 mm. Estimate the settlement in Aug., 1972, if there is double drainage.
11.12 Preliminary settlement analysis for a building indicated a settlement of 50 mm in 4 years and
an ultimate settlement of 250 mm. The average pressure increment in the clay stratum was
30 kN/m^2.
If the following variations occurred in the assumptions, determine the revised value of ultimate
settlement and the settlements at the end of the loading period and that at 3 years after the
completion of the building.
(i) The loading period was 2 years, which was not considered in the preliminary analysis.
(ii) Borings indicated 25% more thickness for the clay layer than originally assumed.
(iii) The water table got lowered permanently during construction by 1.5 metres.