Direction: The ground conditions at a site are as shown in the figure. The water table at the site which was initially at a depth of 5 m below the ground level got permanently lowered to a depth of 15 m below the ground level due to pumping of water over a few years. Assume the following data (i) unit weight of water = 10 kN/m3 .
(ii) unit weight of sand above water table = 18 kN/m3 .
(iii) unit weight of sand and clay below the water tabl = 20 kN/m3 .
(iv) coefficient of volume comprehensibility = 0.25 m2 /MN.
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What is the change in the effective stress in kN/m2 at mid-depth of the clay due to the lowering of the water table?
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- 0
- 20
- 80
- 100
Correct Option: D
Change in effective stress = change in water level × rw .
= (15 – 5) × 10 = 100 kN/m2.
