Mechanical Properties And Crack Propagation Of Rock-like Materials Containing Random Joints Under Uniaxial Compression

Random joints in rock mass seriously affect the stability of rock mass engineering.The study on the mechanical properties,deformation and failure characteristics of randomly jointed rock mass under uniaxial compression has certain theoretical significance and application value for the construction safety and stability control of rock mass engineering.In this paper,cement and gypsum were used as similar materials to prepare rock-like materials with random joints.The strength and deformation parameters of the materials were obtained through indoor uniaxial compression test,and the macroscopic crack distribution morphology and connection degree of the specimens after failure were obtained.The particle flow discrete element software PFC2 D was used to build a numerical model that matches the laboratory test,and the mechanical properties and crack propagation law of rock-like materials with random joints were simulated.Combined with the results from laboratory test and numerical simulation,the influence of random joint size and number on mechanical parameters and crack propagation of the specimens was analyzed.The main conclusions were as follows:(1)With the increase of the size and number of cracks,the uniaxial compressive strength obtained by laboratory test and numerical simulation decreases in a parabolic trend,and the decreasing rate increases gradually.The elastic modulus obtained in laboratory test is slightly smaller than that in numerical simulation,but both of them show a linear downward trend with small amplitude.(2)The mechanical characteristics of the rock-like specimen are similar to that of soft rock.Ductile failure occurs in the process of uniaxial compression and there is a large residual strength.The final failure mode of the specimen is mainly splitting failure.With the increase of the size and number of joints,the macroscopic crack connection degree of rock-like specimens under uniaxial compression presents an approximate linear trend,and the failure degree of the specimens increases.(3)The numerical simulation results indicate that a small amount of cracks appear before the peak,a large number of cracks appear after the peak stress.New cracks are more likely to be generated in the dense place of prefabricated joints.Most of the cracks are tensile cracks(type I cracks),the direction of the tensile cracks is close to the vertical direction,and the shear cracks(type II cracks)are mainly along the direction of 45°.(4)With the increase of the size and number of joints,the inflection point of the crack growth curve in the compression process of the model gradually moves from the peak point to the pre-peak stage,and the axial strain corresponding to the concentrated appearance of the crack becomes smaller and smaller.These results indicate that the increase of the size and number of joints reduces the crack initiation stress of the model,which is more conducive to the crack propagation and connection.The proportion of tensile cracks increases linearly at the peak stress and failure stage,and the total number of microcracks shows a decreasing trend.