Solution of the Ultimate Bearing Capacity at the Tip of a Pile in Anisotropic Discontinuous Rock Mass Based on the Hoek–Brown Criterion

Abstract

An analytical method will be proposed to investigate the bearing mechanism of piles in an anisotropic discontinuous rock mass. Based on the characteristic line method, the discontinuous part of the rock is considered as the boundary condition of the plastified zone, and Riemann's invariant governing equation will be applied at the boundary conditions to link these boundaries. It was found that four different failure mechanisms exist that depend on the inclination angle of weakness planes (χ): (1) conditioned by the planes of weakness in the intermediate zone (MC), (2) conditioned by the planes of weakness close to Boundary 2 in the active zone (M2), (3) conditioned by the planes of weakness close to Boundary 1 in the passive zone (M1), and (4) not conditioned by the planes of weakness (MI). Each pile failure mechanism contains four failure modes under different pile embedment and geostatic loads: (1) deep pile with minor overburden (DL), (2) deep pile and large overburden (DH), (3) semideep pile and small overburden (SL), and (4) semideep pile and large overburden (SH). Therefore, 16 pile failure modes exist and are distinguished by χ and the embedment ratios (n). The friction angles of the weakness planes (φ) have significant effects on the pile failure mechanisms. Under the failure mechanism of MC, M2, and M1, the peak of the percentage of pile bearing capacity in anisotropic discontinuous rock over that in isotropic continuous rock (NβP,DL/NβP,MI ) increased with φ.