Experimental Study On Making Rough Jointed Specimens Based On 3D Printing And Its Deformation And Failure Characteristics

Jointed rock mass exists widely in nature.The discontinuity,heterogeneity and anisotropy of rock mass deformation are caused by the existence of joints,which lead to the extremely complex mechanical properties of jointed rock mass.The strength and deformation of jointed rock have a vital impact on engineering stability.However,whether it is jointed rock mass formed naturally or jointed rock mass produced by excavation unloading,the joint surface is usually not smooth,but roughness.However,in the past,scholars used to assume that joints are smooth or straight-line in the study of mechanical characteristics of compression test of jointed rock mass,due to the limitation of test techniques and means at that time,which caused serious inconsistency with the actual engineering deformation and failure.Therefore,it is of great significance to carry out mechanical compression tests of rough jointed rocks for correctly understanding their mechanical properties and failure mechanism.In this paper,the three-dimensional model of unloading fracture surface of sandstone is reconstructed by advanced three-dimensional scanning and CT technology at home and abroad.The samples with rough joints are prepared by 3D printing technology and pouring of rock similar materials.Then,the deformation and failure characteristics of rocks with rough joints are studied by means of laboratory tests and numerical simulation.The main research results and conclusions are as follows:(1)Conventional triaxial pre-peak unloading tests are carried out on sandstone samples to simulate the unloading failure behavior of surrounding rocks during excavation of chambers in deep strata.Then the main joints of sandstone specimens after unloading failure are scanned by three-dimensional white light and reconstructed by three-dimensional reconstruction.The three-dimensional model of unloading fracture surface is obtained and printed by 3D printer.Then the printed rough joints are prefabricated into rock-like materials by pouring similar materials,and a new method of making samples with rough joints Based on 3D printing technology is proposed.Four kinds of rough jointed samples with different inclination angles,five kinds of rough jointed samples with different scales and five kinds of rough jointed samples with different JRC,a total of 58 samples were prepared.(2)Acoustic emission and digital photography techniques were used to conduct uniaxial tests and conventional triaxial compression tests on rough jointed specimens with 3D printing.The crack evolution and the variation of deformation and fracture characteristics of rough jointed specimens were studied.The results show that the strength and deformation parameters of Rough Joints decrease first and then increase with the increase of inclination angle,decrease with the increase of joint size and increase with the increase of JRC.When confining pressure is 10 and 20 MPa,the smaller the JRC,the easier the shear failure occurs.With the increase of JRC,the specimen begins to develop toward tensile-shear mixed failure and splitting failure.When confining pressure is 30 MPa,the influence of joint roughness on the failure mode of the specimen decreases,and confining pressure plays an absolute control role on the failure mode of the specimen.(3)Based on the above experimental results,the discrete element particle flow model of rock with rough joints is established,and the numerical simulation of three working conditions is carried out.The results show that with the increase of joint JRC,the strain increases when tension crack and shear crack appear,and the tension crack increases with the increase of joint JRC,while the shear crack decreases.The peak strength and modulus of elasticity of specimens decrease with the increase of the number of joints.At the same number of joints,the roughness of joints enhances the strength of specimens.The number of shear cracks increases with the increase of the number of joints.The number of shear cracks in smooth joints is larger than that in rough joints.Joint roughness can obviously improve the shear strength of joints.