RESEARCH ON ROCK MASS CONTAINING DISCONTINUOUS JOINTS BY DIRECT SHEAR TEST BASED ON WEAKENING MECHANISM OF ROCK BRIDGE MECHANICAL PROPERTIES

Based on weakening mechanism for rock bridge mechanical properties,at five different normal stress levels,three different rock mass samples containing discontinuous joints which are tooth-shaped asperities have been studied by laboratory shear test.The tests are conducted with electro-hydraulic servo-controlled shear system.The tests are to study both failure mechanism and strength behavior,displacement behavior of rock mass containing discontinuous joints.At lower angle of tooth-shaped asperities and under lower normal stress,the failure model I is found,which is always in tension failure model.However,at higher angle of tooth-shaped asperities and under higher normal stress,the failure model II is found,which is in first tension but final shear failure.Under the same joint appearance,with the normal stress increasing,both the shear strength and the displacement for peak shear strength raised.However,at the same normal stress,with the joint appearance increasing,the displacement for peak shear strength decreased but the shear strength raised.Moreover,all of cohesion calculated based on Jennings′ theory is higher than the experimental results.Some of angles of friction calculated based on Jennings′ theory are more than the experimental ones.