Study on the Prediction Method of Pile Foundation Bearing Capacity Based on Finite Medium Cavity Expansion Theory

Installation of displacement pile could significantly increase the bearing capacity of pile foundation, and a new analytical method for bearing capacity prediction of displacement pile is proposed based on the elastic-plastic cavity expansion solution in finite soil medium. Mohr-Coulomb yield criterion is used to derive the unified analytical solution for both cylindrical and spherical cavities, assuming the pressure is remained constant at the outer boundary. The solutions are then adopted to analyze the penetration of precast pile, and a mechanical model for pile bearing capacity is constructed. The results show that scale effect is important for cavity expansion. For cylindrical cavities, the cavity pressure and the plastic zone of a finite medium with outer/inner radius ratio greater than 110 is similar to that of infinite medium, whereas the soil expansion curve is comparable for spherical scenarios with outer/inner radius ratio larger than 25. The mechanical model assumes the spherical cavity expansion at the pile end, and pile shaft is taken as cylindrical cavity expansion, which provides the changes of stress field during displacement pile installation and the bearing capacity. The magnitude of pile bearing capacity is compared with existing solution, standard design value, and measured data from field test, validating the proposed novel cavity-expansion based method.