Bearing Capacity of Square and Circular Footings on a Finite Layer of Granular Soil Underlain by a Rigid Base

Traditional bearing capacity theories for the ultimate capacity of shallow foundations assume that the thickness of the bearing stratum is infinite. The presence of a hard layer within a certain depth below the foundation can significantly influence the unit load supported by the soil. Therefore the original bearing capacity equations should be modified to account for this condition in determining the ultimate bearing capacity. In order to evaluate this phenomenon further, model square and circular footing tests were performed on a bed of well-graded sand. Test beds were prepared at three different relative densities corresponding to loose, medium, and dense conditions: Dr=24, 57, and 87%, using five different sand layer thicknesses, H; H/B values of 0.5, 1, 2, 3, and 4, where B is the footing width. Results of the model scale footing tests show that the bearing capacity factor, N(gamma), should be modified up to H/B=3, instead of H/B=1, as previously suggested. The footing shape factor, s(gamma), should account for both shape and finite layering. This technical note gives a description of the test methods and material used and presents the test results in comparison to previous results.