Question

If a maximum settlement of 50 mm is permitted for a raft, the differential settlement must not exceed ___________

(a) 30 mm

(b) 10 mm

(c) 20 mm

(d) 25 mm

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This interesting question is from Shallow Foundations topic in division Shallow Foundations of Geotechnical Engineering II

Answer 1

Correct choice is (c) 20 mm

The explanation is: A raft may undergo large settlement without causing harmful differential settlement. For this reason, almost double settlement of that permitted for footing is acceptable for raft. Therefore if a maximum settlement of 50 mm (2 in) is permitted for a raft, the differential settlement is not likely to exceed 20 mm (0.75 in).