Bearing capacity factor for granular column-reinforced composite ground in saturated soft clay

The effect of the embedded depth of composite ground on its bearing capacity has not been investigated deeply. The bearing capacity of composite ground is underestimated due to the conservative value of embedded depth considered in engineering practice. A finite difference model is established to study the failure mechanism of granular column under rigid foundation and the ultimate bearing capacity factors of granular column-reinforced composite ground without weight. The results indicate that the potential failure modes of granular column-reinforced composite ground can be categorized into shallow foundation failure, composite failure and block foundation failure, depending on the replacement ratio, length of piles and embedded depth. The depth correction factor increases with the length of columns and decreases with the embedded depth. When the length of column and the embedded depth of foundation keep constant, there is an optimum value of replacement ratio to obtain the maximum value of depth correction factor. According to the calculated results, the effect of embedded depth is underestimated by depth correction factor of 1.0 in the existing code. Based on the Mohr-Coulomb yield criterion, a formula for the equivalent strength method of composite ground is deduced and the bearing capacity factor of the shallow failure mode is evaluated by the limit analysis method, which agrees well with the results of finite difference method.