Finite-Element Limit Analysis of Strip and Circular Skirted Footings on Sand

Abstract

The lower- and upper-bound theorems of the limit analysis have been used in conjunction with finite elements and second-order cone programming (SOCP) for determining the bearing capacity of strip and circular skirted footings on sand. The analysis follows the Mohr-Coulomb’s yield criterion and the associated flow rule; sand is not usually considered to obey this rule, but the results of using it are discussed. The friction angle of sand was varied between 30 and 45°, and the depth (Ds) of the skirt increased from 0.25 to 2B; here B implies: (1) the width of a skirted strip footing, and (2) the diameter of a circular skirted footing. The results are expressed in terms of the bearing capacity ratio (BCR): the ratio of the bearing capacities of a skirted footing to that of the surface footing, with the same value of B but without any skirt element. The results reveal that the magnitude of the BCR increases quite extensively with an increase in the value of Ds/B. The skirted footing was found to be especially quite advantageous for loose sand. With the same Ds/B, the BCR for a circular skirted footing was found to be substantially greater than that for the strip skirted footing.