SHEAR MECHANICAL BEHAVIOR OF ROCK MASS CONTAINING Z-TYPE INTERSECTING FRACTURES WITH LABORATORY TEST

We aim to investigate the shear mechanical behavior of rock mass containing fractures. We cut the limestone samples with Z-type intersecting fractures by water knife, and carry out the laboratory direct shear tests. We examine the shear stress-displacement curve, analyze the influence of prefabricated fissure angle and normal pressure on the strength, deformation and crack coalescence and explore the failure evolution mechanism. The results indicate the follows: (1)The shear stress-displacement curve can be divided into four deformation and failure stages including prefabricated fracture and pore compaction stage(initial sag), quasi-linear deformation stage(intermediate linear fluctuation), pre-peak unstable fracture development stage(later convex) and post-peak strength residual stage(steep drop). (2)The peak shear stress of specimens increases with the normal stress at the same fissure angle(nearly linear) and decreases with the increase of fissure angle at the same normal pressure(the trend is slowing down). (3)The evolution of macroscopic crack damage can be divided into three stages, including initial compression elastic stage, crack growth stage and through fracture failure stage. The failure modes can be divided into three types, i.e., tensile failure, shear failure and tension-shear mixed failure. The last one can be divided into two types, i.e., tension-shear hole-through and shear-stretch-shear hole-through.