A new shear strength criterion for rock discontinuities considering roughness degradation and loading rate effect

The degradation of surface roughness of rock discontinuities under cycling loading weakens shear strength with the accumulating shear displacement. This effect enlightens us to propose a new shear strength criterion for rock discontinuities based on the law of JRC (joint roughness coefficient) degradation and Barton's shear strength equation, which would be critical for determining the permanent displacement and thus the stability of rock slope under seismic loading. The effect of loading rate on roughness degradation has been included in our model of JRC degradation. The comparison with previous analytical models on predicting the degradation of JRC after cycling loading suggests a good accuracy of our model. In compensation to previous direct shear experiments concerning cyclic loading, we carried out cyclic shearing experiments on granite rock discontinuities to put constraints on the coefficient of degradation rate used in our model. Opposite to previous considerations, we suggest more factors would control the degradation rate, including the normal stress, the joint wall strength, the initial roughness, the loading rate and the cycling amplitude, and their effects have been discussed based on experimental data.