Mechanical properties and failure mode of rock mass containing V-type intersecting fissures

In order to understand the mechanical properties and crack evolution of rock mass specimens con-taining V- type intersecting fissures,some conventional uniaxial compression tests on specimens containing V-type intersecting fis- sures with different intersection angles were carried out by using the MTS815 elec-tro-hydraulic servo control test ma- chine. Based on the experimental results,the stress-strain curves,strength and deformation characteristics,crack evolution and failure modes,energy dissipation characteristics of specimens were analyzed in detail. The main conclusions were drawn as follows:① the stress-strain curves of fissured specimens enter the stage of crack initiation and propaga- tion earlier than that of intact specimens,and show obvious stress drops before the peak stress is reached. In the stage of post-peak failure,the stress-strain curves of intact specimens drop rapidly,while those of fissured specimens fall multi-stage,and even horizontal extension slowly declines,showing obvious ductile failure characteristics. ② The peak stress,modulus of elasticity and peak strain of the fissured specimens decrease obviously. Peak strength and modulus of elasticity increase first and then decrease with the increase of intersection angle. Axial peak strain decreases linearly with the increase of the intersection angle,which is mainly affected by the intersection angle of fissures. ③ The exist- ence of fissures can completely change the failure mode of the fissure. With the increase of intersection angle,the evo- lution process of the failure modes of specimens is: step-type tensile-shear complex failure ( 30°) → tensile and splayed-shear complex failure (60°)→ step-type parallel double inclined plane shear failure (90°). When the inter- section angle is 60°,the crack evolution and failure modes of the specimens show approximate structural symmetry rel- ative to loading direction. ④ The elastic strain energy,dissipated energy,total energy and dissipated energy rate of the fissured specimens under uniaxial compression are significantly lower than those of intact specimens. The more the number of cracks,the more obvious the surface shedding phenomenon,so then the greater the dissipated energy and dissipated energy rate. Tensile-shear complex failure consumes more energy than single shear failure. The failure char- acteristics and failure modes of the fissured specimens can well reflect its energy dissipation characteristics.