Influence Of Rock Mass Joint Aperture On Its Dynamic Closure Characteristics Experimental Study

The rock mass in nature is usually composed of rock and discontinuous plane,and the discontinuous plane without significant relative displacement is also called joint.Because the rock is affected by the claimed stress,there would be pores between the joints,which is also called tension joint.Jointed rock masses are characterized by discontinuity,inhomogeneity,anisotropy.As known as China is the country with frequent earthquakes,so that the study of jointed rock mass is of great importance to engineering blasting,seismic analysis and other practical projects.Large numbers of studies have shown that rock joints have a significant effect on the mechanical properties of rock mass,especially the dynamic mechanical properties and stress wave propagation.The effects of joint aperture on stress wave propagation,joint dynamic mechanical properties and joint morphology are studied in this paper.Firstly,the Split Hopkinson Pressure Bar(SHPB)is used to carry out multiple impact experiments on joint specimens with different joint aperture.On the other hand,the influence of joint aperture on stress wave propagation is studied by transmission coefficient.On the other hand,the influence of joint aperture on dynamic mechanical properties of joints is studied from deformation modulus and equivalent normal stiffness of joints.The experimental results show that increasing joint aperture will weaken the stress wave transmission effect and reduce the specimen deformation modulus and equivalent joint normal stiffness.After that,the SHPB is adopted to carry on the cyclic loading to the specimen with different joint bugle distribution mode.The joint bugle distribution here is mainly described from the angle of trapezoid joint concentration degree and trapezoid joint quantity.The experimental results show that in the case of joint aperture and the same consistency of the joint,the more the joint bulge,the greater the transmission coefficient,the deformation modulus and the equivalent joint normal stiffness,the smaller the closure of the peak joint but the change range is limited,the more to the center of the specimen,the transmission coefficient,the greater the equivalent stiffness of the deformation modulus and the joint,and the joint normal closure is reduced but the change range is also small.Finally,3D scanning techniques have been used to scan the joint morphology of the specimens before and after the experiment to analyzing the joint surface deviation and joint surface fracture development before and after the experiment and study the damage position and crack development law of the joint surface.In addition,analysing volume change rate of joint part to explore the joint aperture and Joint Bulge Distribution,the result shows that keeping the same JMC and Joint Bulge Distribution,Under cyclic impact,the more joint aperture,the greater the joint appearance changes,also in the same distribution mode of the joint bulge,the larger the joint gap volume ratio,the greater the change of the joint appearance,the more discrete the joint distribution,the center of the joint convex concentration,the smaller the joint appearance change.