The objective of this study is to determine the shearing resistance of fractures in Tak granite as affected by orthotropic stress states where σ1≠σ2≠σ3. Triaxial shear tests are performed to obtain the strengths and dilations of tension-induced fractures and smooth saw-cut surfaces under confining pressures up to 18 MPa. The ratios of the lateral stresses vary from 0 to 4. The shearing resistance, dilation and areas of sheared-off asperities of the rough fractures decrease when the lateral stress ratios increase. The shear strengths of smooth saw-cut surfaces tend to be independent of the stress ratios. The distortional strain energy (Wd) required to displace the fractures under various stress states increases linearly with the mean strain energy (Wm). The energy ratio (Wd/Wm) in terms of the strains and dilation can be used as a predictive tool for the movements of faults or fractures in Tak granite.
