Investigation on the shear properties of discontinuities at the interface between different rock types in the Badong formation, China

Recent research has paid little attention to the difference in shear strength between discontinuities with different joint wall material (DDJM) and discontinuities with identical joint wall material (DIJM) and what are the controlling factors of shear properties of DDJM. Bedding planes between argillaceous limestone and mudstone in the Badong formation in the Three Gorges area of China were investigated using physical model tests. The effect of joint wall material combination on the shear properties of DDJM was first revealed by conducting tests on a series of artificial joint specimens that were made of different joint wall materials and with varying joint surface topographies under different normal stresses. The results indicate that: the peak shear strength of DDJM is not equal to the lower peak shear strength of DIJM for two joint wall materials of the DDJM, even so it is closer to the lower peak shear strength than to the higher one; effect of joint roughness and normal stress on peak shear strength of DDJM is similar with DIJM; effect of joint wall material combination on peak shear strength of DDJM is greater with larger roughness and higher normal stresses. Based on the data acquired from the physical model tests, a new empirical equation to estimate the peak shear strength of DDJM was developed. The capability of the equation was validated by comparing estimates with data from direct shear tests on natural DDJM samples gained from the Badong formation. Finally, the proposed empirical equation was applied to the stability analysis of a rock slope in the Badong formation.