Failure Characteristics Of Jointed Rock Mass Under Blasting

Natural rock masses are not homogeneous rock masses,and there are often a large number of weak structural planes such as joints,fissures,and bedding.The existence of these weak structural planes seriously affects the dynamic properties of rock masses.Therefore,it is of great significance to study the failure characteristics of jointed rock mass under dynamic load.In this paper,for the rock mass of a limestone mine,based on the static chamber test,the pendulum impact chamber test is used as the means to analyze the stress wave characteristics of parallel joints,granite-containing cement joints and intersecting joints in rock specimens.The dynamic compressive strength characteristics were studied,and the failure mode law of jointed rock specimens was revealed.The influence of joint geometry on joint rock mass failure and process under step blasting was simulated by using discrete element numerical simulation software.The following conclusions were obtained:(1)In the Brazilian split test,when θ is 0°,the rock sample is mainly subjected to tensile-pull fracture.when θ is 30°,the rock sample is mainly damaged by the pullslip.At 45° or 60°,the rock specimen is mainly damaged by slippage.when θ is 90°,the cracking of the weak filler along the structural plane is broken.(2)Under the impact load of limestone,there are two main failure modes.when the joint inclination angle is 30°,45°,60°,the rock specimen damage is mainly caused by shear failure,and the joint control is more obvious.When it is 0°,75°,80° and 90°,the rock samples are mainly damaged by splitting and are not obvious by joint control.For intersecting joints,the failure zone of the rock is mainly concentrated in the intersection of joints,and the existence of non-penetrating joints will aggravate the damage of the specimen to some extent.for joints with higher strength of cemented materials,the specimens of rock damage is not affected to some extent by the angle of inclination and the thickness,instead of penetrating the joint,it sometimes induces the damage of the rock and affects the block size after the rock sample is destroyed.(3)For the limestone specimens with different parallel joint numbers,when the joint inclination angle θ is 90°,the failure mode of the rock specimen is not changed with the increase of the number of joints compared with the complete specimen,with the increase of the number Of joints,The dynamic compressive strength of the rock sample is reduced.When the joint inclination angle is 60° in the intersecting joint,the decrease is larger as the number of joints increases.(4)The inclined joint has a great influence on the propagation of stress waves in the rock mass,and the displacement amount perpendicular to the joint direction in the radial crack propagation direction of the blasthole is concentrated.At the same time,it can be known that the larger the joint thickness,the more concentrated the displacement is at the joint,the stronger the reflection of the stress wave at the joint,and the weaker the transmission capacity.For intersecting joints,the concentration of stress waves is easy to occur at the intersection of joints,and the displacement is concentrated at the intersection of joints,indicating that the joints are prone to damage at the intersection of joints.During the step blasting process,the damage of the joint distribution area is more serious,and the stress wave energy attenuation occurs at the joint,and the stress wave is concentrated at the joint.