Dynamic Mechanics Of Rock Filled Joints Considering Cumulative Damage Effects Characteristic Test Research

Rock Joints are natural and most widely exists in the geological structure of rock mass,the existence of the joint will divide the discontinuous rock mass into heterogeneous anisotropic geologic body,which significantly affects the engineering properties of rock mass.Generally,the joint often contains some fillings.Because of the existence of fillings,the mechanical properties of jointed rock mass are complex.When the stress wave produced by earthquake blasting and the impact load propagates in the filled jointed rock,the wave energy dissipation,the wave velocity decreases and the amplitude attenuation of stress wave will occur.In general,blasting works in rock engineering cannot be completed at one time,but gradually operated in different regions.Thus,multiple blasting works will inevitably cause cumulative damage to jointed rock mass in the non-excavation area,After repeated cumulative impact,the jointed rock mass will inevitably cause damage to the filling layer,which will lead to the deterioration of the overall strength of the rock mass,reduce its stability,and intensify the attenuation of stress wave in the jointed rock mass.Therefore,it is of great significance to study the dynamic characteristics and cumulative damage law of filling joints under the action of dynamic and static loads and cumulative preloading to improve the stability and safety protection of many projects..In this paper,the static and dynamic characteristics of the artificial filled jointed rock samples,the cumulative damage of the samples under the condition of multiple impacts and the influence of cumulative damage on the dynamic characteristics of the filled joint are studied by series of laboratory tests.Firstly,the mechanical properties of filled joints under static compression and dynamic impact are studied by universal testing machine and SHPB device respectively.Then,based on the mechanical characteristics of filled joint,the wave velocity changes and damage rules of jointed rock samples under cumulative impacts are analyzed by using the simple drop hammer impact device and wave velocity instrument.Finally,the SHPB dynamic impact tests are conducted on the jointed rock samples after cumulative impacts,and the law of strength deformation characteristics,energy dissipation,damage evolution and other laws of filled joints considering cumulative damage effect are analyzed.The results show that the strength and thickness of the joint fillings have a controlling effect on the static and dynamic mechanical strength of the filled rock joint,and the failure mode of the joint is mainly related to the property strength of the filling material.In the filled joint,the fillings hinder the transmission of stress wave,which is mainly reflected in the change of wave impedance of rock specimen caused by the change of strength and thickness of the filling material.The energy dissipation ratio under impact compression decreases with the increase of the filling joint thickness and increases with the increase of the strength of the joint filling,which reflects the change of the energy required to cause the filling joint failure.With the increase of cumulative impact times,the cumulative damage degree presents a nonlinear increasing law and establish damage evolution model of filling joints under cumulative impact.With the increase of cumulative damage,the dynamic peak stress of the filled joint decreases while the dynamic failure strain increases gradually,which indicates that the ability of the filled joint to resist the external impact decreases gradually,In addition,the influence of cumulative damage on the dynamic characteristics of filled joint also changes with the change of filling thickness and filling material strength.The cumulative impact has a significant effect on the propagation of stress waves in the filled jointed rock mass.With the increase of cumulative impact times,the transmission effect of stress waves propagating in the filled joint is gradually weakened,and the corresponding reflection effect is gradually enhanced.