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 T₀, α, and β. Parameters α and β 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.