Formula of Passive Earth Pressure and Prediction of Tunneling-Induced Settlement in Anisotropic Ground Based on a Simple Method

The existence of soil anisotropy makes the strength and deformation of the ground dependent on the loading direction, which should be considered in some geotechnical engineering designs. This paper introduces the anisotropic transformed stress method that generalizes the isotropic failure criterion and constitutive model for anisotropic cases through modifying the stress. This method brings much convenience for the solution of practical problems in the anisotropic ground. The anisotropic Mohr-Coulomb failure criterion is still a linear function of stress since the internal friction angle and cohesion remain constant along different directions. A simple and explicit formula for the passive earth pressure, which adds only an influence coefficient of soil anisotropy to Rankine's formula, is derived. The elastoplastic stiffness matrix of the anisotropic modified Cam-Clay constitutive model does not increase any extra item compared with its general expression, so that finite-element simulation can be easily conducted to predict the surface settlement induced by tunnel excavation. Based on the aforementioned formula and simulation, the degree of anisotropy and the depositional direction of the ground on the effects of the passive earth pressure and the surface settlement trough are systematically analyzed.