(a) A long footing, 3 ft wide, is to be installed 4 ft below grade. Drained shear tests indicate that the supporting soil has a cohesive strength of 900 psf and the angle of internal friction is 20°....

(a) A long footing, 3 ft wide, is to be installed 4 ft below grade. Drained shear tests indicate that the supporting soil has a cohesive strength of 900 psf and the angle of internal friction is 20°. The soil rigidity index is greater than the critical index. The soil unit weight is 115 pcf and the water table is deep. Calculate the safe bearing capacity, applying a factor is safety of 3 to the extended bearing capacity equation. Assume that the backfill is not well compacted and the depth factors do not apply.

(b) Determine the design bearing capacity if the depth factors do apply (all other conditions of part a are the same). What percent change in the design bearing capacity results from including the depth factors?

(c) Recalculate the bearing capacity for the conditions of part a but where the groundwater table is at the soil surface.