Abstract
The shear strength of a rock joint has been focussed by many engineers over several decades. So far as the authors know, there are many publications concerning the shear test under constant normal load and/or stiffness. In consideration of allowable limit of displacement/deformation associated with rock tunnelling, we should pay more attention to the meaning of the shear behavior of rock joints under constant dilatancy than the one under constant normal load and stiffness, which is much far from the reality in rock tunneling with loosening phenomenon. By employing more than 140 specimens which were reproduced from 20 natural joints with different roughnesses, the authors have carried out direct shear tests under both constant pressures and dilatancies.
The breakage of joint asperity was discussed from the point of view standing on the relationship between the loss of asperity and mobilized shear strength. The change of shear strength from the peak to the residual strength has been clarified and the appropriate installation of supporting elements in rock tunnelling was discussed.
