Abstract: The failure of surrounding rock during excavation can be generally grouped into two categories: tensile failure and compressive-shear failure. The cracks induced by the two failure types exhibit different mesoscopic configurations, which lead to different permeability evolutions of rock with tensile and compressive-shear cracks. The tensile and compressive-shear cracks of granites are firstly generated by triaxial compression tests under different confining pressures and the permeability tests are conducted on the samples with tensile and compressive-shear cracks. It is shown that the permeability of tensile cracks is more sensitive to hydrostatic pressure. In order to analyze the mesomechanical structures of cracks, the scanning electron microscope tests are also performed on the surfaces of tensile and compressive-shear cracks. The tensile cracks dominated by axial compression tests and the crack surfaces are relatively smooth. With the increase of confining pressure, the mesomechanical structures of cracks surfaces change significantly, more and more compressive-shear cracks are generated on the crack surfaces, and the crack surfaces are relatively rough. Under hydrostatic stress, the tensile cracks can be easily closed, while the concave-convex configuration of compressive-shear cracks can prevent the closure to some extent. The evolutions of permeability of granites with tensile and compressive-shear cracks are essentially dependent on the mesomechanical structures of cracks surface. The above results are helpful in determining the permeability of the surrounding rock in underground engineering.

Key words: permeability, granite, triaxial compression, tensile and compressive-shear cracks, micromechanical structure