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Read the following statements:
(P) While designing a shallow footing in sandy soil, monsoon season is considered for critical design in terms of bearing capacity.
(Q) For slope stability of an earthen dam, sudden drawdown is never a critical condition.
(R) In a sandy sea beach, quicksand condition can arise only if the critical hydraulic gradient exceeds the existing hydraulic gradient.
(S) The active earth thrust on a rigid retaining wall supporting homogeneous cohesionless backfill will reduce with the lowering of water table in the backfill.
Which one of the following combinations is correct?
- (P)-True, (Q)-False, (R)-False, (S)-False
- (P)-False, (Q)-True, (R)-True, (S)-True
- (P)-True, (Q)-False, (R)-True, (S)-True
- (P)-False, (Q)-True, (R)-False, (S)-False
Correct answer: (P)-True, (Q)-False, (R)-True, (S)-True
Solution
Statement (P) is correct because monsoon conditions can significantly affect the bearing capacity of sandy soils due to increased water content. Statement (Q) is false as sudden drawdown can indeed create critical conditions for slope stability in earthen dams. Statement (R) is true since quicksand conditions occur when the hydraulic gradient exceeds a critical threshold. Statement (S) is also true because lowering the water table reduces the pore water pressure, thereby decreasing the active earth thrust on the retaining wall.
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