Upper bound analysis of rectangular surface footings on clay with linearly increasing strength

Abstract

The ultimate bearing capacity problem of rectangular surface footing over undrained clay with linearly increased strength is comprehensively analyzed with a numerical upper-bound method. For uniform soil, the present results are generally in accordance with available results and present the best upper-bound prediction when the three-dimensional effect is predominant. The obtained bearing capacity factor for nonhomogeneous soil decreases with the increase of width-length ratio, totally different from that of uniform soil. Accordingly, the shape factor also varies greatly with strength nonhomogeneity. Possible reasons are discussed based on the underlying velocity field. Finally, a strip footing based design equation considering such effect is proposed for the vertical bearing capacity of rectangular surface footings.