CSLB General Building (B)Site Work, Foundations and ConcreteHard
A soils report specifies an allowable bearing capacity of 2,000 pounds per square foot for a site. A contractor designs an isolated column footing measuring 2 feet by 2 feet to support a total column load of 10,000 pounds. Is this footing adequate?
- AYes, because the resulting soil pressure of 1,500 psf is below the allowable limit
- BNo, because the resulting soil pressure of 2,500 psf exceeds the allowable limit
- CNo, because the resulting soil pressure of 5,000 psf far exceeds the allowable limit
- DYes, because the resulting soil pressure of 2,000 psf exactly equals the allowable limit
Show answer & explanationAnswer & explanation
Correct answer: B. No, because the resulting soil pressure of 2,500 psf exceeds the allowable limit
The footing area is 2 ft x 2 ft = 4 square feet. Soil pressure = load / area = 10,000 lb / 4 sq ft = 2,500 psf, which exceeds the allowable bearing capacity of 2,000 psf, so the footing is undersized and must be enlarged.
Why the other options are wrong
- A. Incorrect pressure calculation; 1,500 psf does not match the given values.
- C. Incorrect; 5,000 psf misapplies the area calculation.
- D. Incorrect; the actual calculated pressure exceeds, not equals, 2,000 psf.
Soil Bearing Pressure Check
Verifying that the pressure a footing transmits to the soil (load divided by footing area) does not exceed the allowable bearing capacity from the soils report.
- Soil pressure = total load ÷ footing area
- Must be less than or equal to allowable bearing capacity
- If pressure exceeds capacity, footing must be widened or soil improved
Memory trick: Divide the load by the footprint to see if the soil can take the weight.