The safe bearing pressure for a raft foundation on sand is found to be higher than that for an individual footing because
- Athe permissible total settlement is twice than that of a footing
- Bthe density of sand decreases with depth
- Cthe differential settlement is less for a raftCorrect
- Dthe raft is thicker than individual footings
Solution
Concept
Raft on sand
Step-by-step solution
1. A raft is stiff and spreads the load, so differential settlement is small. 2. Safe pressure on sand is governed by settlement, so it can be higher for a raft.
Explanation
Less differential settlement allows a higher bearing pressure.
Why the other options are wrong
The density of sand increases with depth, and thickness is not the reason.
Correct answer: C) the differential settlement is less for a raft