Abstract
In consideration of allowable limit of displacement and deformation associated with rock tunnelling, we should pay more attention to the meaning of the shear behavior of rock joints under constant dilatancy. By employing about 250 specimens which were made of three materials and reproduced from several natural joints with different roughnesses, the authors have carried out direct shear tests under constant dilatancies. The breakage of joint asperity was discussed from the point of view standing on the relationship between shear strength and the loss of asperity. The method to estimate the volume of fractured asperities was proposed and the correlation between shear strength and the volume was discussed. Finally, the authors proposed the new relational expression between the volume of fractured asperities and the shear strength.
