Shear Strength Property of Rock Joint Induced by Joint Roughness

Daishi HIROSAKI

Satoru OHTSUKA

Rock joint greatly affects the stability of rock. Shear strength of rock joint is well known to depend on many factors as joint roughness, acting normal stress and strength parameter of rock. Barton (1972) proposed shear strength model by introducing JRC to express joint roughness. But, it has a drawback on objectivity with respect to decision of JRC. In this study, the relationship between joint roughness and shear strength was shown by upper boundary calculations, and the shear strength model was newly proposed by applying Rengers (1970) method to evaluate joint roughness objectively. The Rengers method gives the maximum angle of inclination in roughness for the specific investigation length. The maximum angle of inclination relates to dilatancy induced by shearing rock joint. It was made clear the proposed method estimated shear strength properly for Barton's experiments and his experimental model for low acting normal stress. Anisotropic strength of rock joint for shearing direction was analyzed with the proposed method. It was clearly observed for regular joint, but not for irregular joint. It denotes the shear strength of rock joint could be estimated by roughness only. Shape analysis of excavated rock planes was conducted for different rock type and classification. Obtained Rengers curves were similar for different rock type and classification. It was apparent that normalization of Rengers curve by angle of shear resistance could be unique. Even though limited cases, this suggests the possibility on estimation of joint roughness by rock type and classification.