______ is the maximum net intensity of loading that can be allowed on the soil without the settlement exceeding the permissible value.
Try it first: pick an option, then read the explanation.
Asked in SSC JE 16/11/2022
Detailed Explanation
Bearing capacity terms come in two families: those based on shear failure (ultimate and safe bearing capacity) and the one based on settlement (safe bearing pressure).
Why “Safe bearing pressure” Is Correct
The safe bearing pressure (also called the net soil pressure for a specified settlement) is the largest net pressure under which the settlement just reaches the permissible limit, e.g. 25 mm or 40 mm. It is the settlement criterion; combined with the shear criterion, it gives the allowable bearing pressure.
| Term | Meaning |
|---|---|
| Gross ultimate bearing capacity, qu | Total pressure at the base of the footing that causes shear failure |
| Net ultimate bearing capacity, qnu | qu − γDf (pressure in excess of the overburden removed) |
| Net safe bearing capacity, qns | qnu ÷ factor of safety (usually 2.5 to 3) — safe against shear only |
| Safe bearing pressure (settlement) | Net pressure at which settlement just reaches the permissible value |
| Allowable bearing pressure, qa | Lower of the two: safe against shear failure AND settlement within limits |
Why the Other Options Are Wrong
- A. Gross safe bearing capacity: Gross safe bearing capacity is based on shear failure (net safe + γDf), not on settlement.
- B. Ultimate bearing capacity: Ultimate bearing capacity is the pressure at shear failure, with no factor of safety.
- D. Net pressure: Net pressure is simply the pressure in excess of the overburden, not a capacity.
Key Point
Safe bearing pressure = settlement criterion; safe bearing capacity = shear criterion.
Key Concepts for Students
- Allowable bearing pressure is the lower of the two.
- Plate load tests help estimate settlement for this check.
- Permissible settlements are set by codes (e.g. IS 1904).
Practice more: this is question 18 in Shallow and Deep Foundation MCQs – Part 2. Try the whole set and check every answer instantly.