Evaluating the stability of anti-dip slate slope using an innovative failure criterion for foliation

Toppling failure is one main failure types of anti-dip slate slopes, and is strongly affected by the mechanical properties of foliation. This study conducted a series of pull-off tests and direct shear tests on slate foliation to obtain its failure envelope, and an innovative failure criterion was accordingly proposed. The proposed failure criterion exhibits a nonlinear trend in the low normal stress range; considers both tensile and shear strengths, and has three material parameters - tensile strength T-0, alpha, and beta. Parameters alpha and beta are related to the slope variation of the failure criterion. To investigate the effectiveness of the proposed failure criterion on the evaluation of slope stability, it is implemented in a discrete element code UDEC and a simulation was carried out to evaluate the deformation and failure pattern of an anti-dip slate slope. The results of the UDEC analysis demonstrate that the simulated failure pattern and deformation characteristics agree with that of an actual anti-dip slate slope. The proposed failure criterion of foliation and the Mohr-Coulomb criterion are further compared in slope stability analysis. The proposed failure envelope accurately reflects the tensile strength and shear strength under low normal stress, but the Mohr-Coulomb criterion apparently overestimates the strength in this stress range. Therefore, the proposed criterion is more effective than the existing criteria in predicting the toppling failure of slate slopes.