Experimental Study On Dynamic Mechanical Properties Of Joints Under Different Penetration Rates

Rock is a geological body formed by the long-term geological processes of various minerals,and many of the projects that are closely related to us,such as transportation,water conservancy,mining,and human defense,are found everywhere.As a kind of natural material,rock often contains the microscopic or macroscopic natural defects such as cracks,holes and joints,and the existence of rock joints makes the rock structure appear discontinuous and uneven,which also seriously affects the mechanical properties of rock.Many rock engineering disasters happen all has close relationship with the existence of rock joints,crushing,especially in the ore-bearing rock blasting,coal mining and nuclear explosion protection involves rock dynamic nature of the project.When dealing with engineering problems related to rock dynamic mechanics,it is necessary to pay attention to the influence of joints on the mechanical properties of rocks.In this paper,a separated Hopkinson pressure bar system is used to compare the rock specimens with different joints and the cement mortar specimens.The dynamic mechanical properties of rock specimens and cement mortar specimens with different joints under impact load are studied,and the influence of penetration degree on dynamic mechanical properties of jointed rock and cement mortar is analyzed.The results show that the change of joints has a great influence on the dynamic compressive strength of the joints,1/4,1/2,3/4 penetration and full penetration peak joint dynamic compressive strength of the specimens decreases continuously with increase of joint penetration degree,and the rate and the decrease of the dynamic strength increases gradually with the increasing penetration degree of the joint position.As the joint rock penetration degree increasing,joint specimen strain rate is getting higher,that incident stress wave in the joint had more reflection,maximum strain rate appeared in the all through joint specimens,and joint position,joint angle and specimen length to diameter ratio of different rock dynamic compressive strength and the influence of strain rate change with penetration degree is not big.To the research of single joint rock,when the joint rock penetration degree no more than a quarter,joints and rock damage forms mainly tension damage,with the increase of joint penetration degree,joint form of rock damage is from the tensile failure to shear failure is given priority todevelopment.