Experimental Study On Failure Mechanism And Stress Wave Propagation Of Joint Rock Mass

In nature,natural rock mass has a large number of mature joints.Due to the existence of joints,the mechanical properties and conduction characteristics of rock mass have undergone significant changes.When the stress wave propagates in the jointed rock mass,it will be seriously attenuated,causing dynamic disasters such as rock mass instability,and seriously affecting the quality and safety of the project.Therefore,with the increasing excavation depth of underground engineering,the in-depth study of nonlinear failure characteristics of deep jointed rock mass has important guiding significance for engineering design and safe construction.Southwest China is rich in the junction area of sandstone and hard rock.Studying the dynamic characteristics of soft rock under impact load can reduce unnecessary economic losses for underground construction.Therefore,on the basis of previous research,the number of joints and weak interlayers have been considered.The thickness and the material at both ends of the joint are three factors,and the similar theorem is used to match the rock-like materials of soft sandstone and hard rock,and a total of 8 sets of test pieces are produced.By means of analysis and ABAQUS numerical simulation,the dynamic failure mechanism and stress wave propagation law of multi-joint rock-like materials were systematically studied.The research contents include: waveform change of stress wave propagation,transmission coefficient,energy change,stress-strain curve,failure process analysis,stress field change,etc.The specific research results are as follows:(1)The experimental group of the same material with different number of joints shows that: the larger the number of joints,the greater the peak value of the incident wave and the reflected wave,the transmission wave has attenuation phenomenon in the propagation,and only a few stress waves pass through the jointed rock specimen.The energy passed through the specimen to the transmission rod to form a transmission wave,and the transmission coefficient gradually decreased with the increase of the number of joints;the degree of damage increased with the increase of the number of joints,which all showed mixed tension-shear failure;energy consumption There is no specific and obvious relationship between the dispersion and the number of joints,but the more joint surfaces,the smaller the transmitted energy;from the stress-strain curve,the dynamic compressive strength of the single-joint specimen is the largest,and the increase of the number of joints changes the failure mode of the specimen.With the increase of the number of joints,the Mises stress of the specimen gradually disperses towards the ends of the specimen near the end faces.As the number of joints increases,the maximum principal stress concentration area in the specimen increases,and the greater the number of joints,the easier the maximum principal stress is to express.in the form of compressive stress.(2)The experimental groups with different thicknesses of weak interlayers show that with the increase of the thickness of the filling joint,the reflected wave and the transmitted wave show a decreasing trend.,with the increase of the thickness of the weak interlayer,the transmission coefficients all decrease,and the amplitude shows an upward trend;due to the plastic characteristics of the specimens,the specimens are compressed and become bulging during the failure process,and the specimens all show The tensionshear mixed failure appears,the shear failure of the joint end face and the thickness of the weak interlayer increases,and the failure of the right end of the specimen is more sufficient;the energy dissipation ratio increases with the increase of the thickness of the weak interlayer,and the larger the thickness of the weak interlayer is The lower the transmission energy ratio is;the peak strength of joint soft rock failure is closely related to the joint filling thickness,and it increases with the filling thickness in a positive correlation form,and the dynamic elastic modulus of the thick interlayer specimen is larger than that of the thinner interlayer.The thicker the interlayer,the weaker the Mises stress distribution near the interlayer.Continuing to load the Mises stress will concentrate on the weak interlayer,which will lead to the failure of the weak interlayer first.(3)From the perspective of different material groups of a single joint: the amplitude of the incident wave decreases with the decrease of the material strength.When the difference between the softness and hardness of the material at both ends of the joint surface is larger,the joint has a more obvious blocking effect on the propagation of the stress wave;the greater the difference in material strength,When the strength of the joint material decreases,the hard rock part is less likely to be damaged,and the whole process is a mixed tension-shear failure;the energy dissipation during the stress wave transmission process decreases with the decrease of the strength of the joint material.The lower the strength,the transmission of the incident stress wave The smaller the energy,the larger the dynamic elastic modulus of the harder material group(material AC),the closer the strength of the materials on both sides of the joint is,the more brittle it is,and the more plastic it is.Mises stress is mostly concentrated in the softer material,and when the strength difference between soft and hard materials is greater,the softer material is more likely to accumulate Mises stress and thus more fully damaged.The smaller the maximum principal stress of,and the weaker the material at the right end,the easier it is to show the form of compressive stress.