UNDRAINED LIMIT ANALYSES FOR COMBINED LOADING OF STRIP FOOTINGS ON CLAY

This paper applies numerical limit analyses to evaluate the undrained stability of surface footings on nonhomogeneous and layered clay depos its under the combined effects of vertical, horizontal, and moment (V, H, M) loading. The analyses are able to resolve the true collapse loa ds to within +/-5% by computing rigorous upper and lower bound solutio ns for these plane strain problems using linear programming methods an d finite element discretization. The results focus on the geometry of the three-dimensional failure envelope and illustrate the effects of u nderbase suction and non-homogeneous undrained strength profiles. The existing empirical bearing capacity factors for inclined, eccentric lo ading are conservative, often underestimating the exact collapse solut ions for footings on homogeneous clay by more than 25%. However, the s ame correction factors can become completely unreliable when there is a significant undrained strength gradient. The numerically-derived fai lure envelope for footings on homogeneous clay is described approximat ely by curve fitting techniques using relatively simple functions that can be used to update the existing bearing capacity factors.