Effects of the lattice leg on cavities and bearing capacity of deeply embedded spudcans in clay

Abstract

This paper examines the effect of the lattice leg on the cavities of deeply embedded spudcans in clays using centrifuge model tests and finite-element analyses. The lattice legs are characterised by two parameters, namely the opening ratio and area ratio. Both centrifuge and numerical results show that, in the presence of lattice legs, the cavities consist of two zones: a deep inner cavity within the cross-sections of the lattice legs and a much shallower outer cavity beyond the periphery of the lattice legs. The latter can be attributed to cavity wall collapse around the rim. The volume contributed by the outer cavity is much smaller than that contributed by the inner cavity. Hence, the latter is the focus of this study. The findings show that the lattice leg affects the cavity in two ways. First, it restricts soil back-flow to the region outside the lattice leg. Second, it enhances the stability of the soil on the walls of the cavity, thereby limiting the wall collapse zone to the topmost portion of the cavity. Both of these effects contribute to an increase in the cavity depth. Based on the centrifuge model test results and finite-element analyses, relations are proposed to predict the inner cavity depth which incorporates the opening and area ratios of the lattice leg, spudcan diameter and undrained shear strength of the soil. The effect of the lattice leg on bearing capacity is also illustrated using centrifuge results. Finally, the possibility of cavity wall collapse and spudcan settlement due to consolidation of soil and cyclic loading are briefly discussed using centrifuge data.