Instability Mechanism And Mechanical Size Effect Of 3D Printed Surrouding Rock Model

Several challenging and problems of rock mass engineering have emerged in engineering construction in China.The geological model test is one of the most used research methods in studying disaster mechanisms and stability analysis in rock engineering.Still,these models often have complex geometric structures and great difficulty in making.Moreover,the rock mass is a discontinuous and heterogeneous medium,resulting in the differences between the testing model and the engineering prototype because of the size effect.In this paper,a 3D printing method based on additive manufacture and subtract manufacture technology is developed to realize the intelligent,accurate,and controllable production of geological models of various sizes.Combined with theoretical analysis and numerical simulation,fractured surrounding rock stability and multiple size-effect are studied.Relevant results are applied to the underground caverns in Jinping Hydropower Station.The main contents and conclusions of this paper are as follows:(1)3D printing method of the fractured rock mass modelA 3D printing geological model system with two robot arms is developed based on additive and subtract manufacturing.And a kind of rock-like material suitable for 3D printing is designed to make discontinuous geological models.The printing performance and forming accuracy of the geological model are tested.It is proved that the geological model produced by 3D printing has the automation advantages,forming accuracy and simulation,which solves the problems that the complex geological test model is challenging to make,repeat and control.(2)Verification of 3D printed rock mass model in mechanical testThe rock mass models with different fractures are made by the 3D printing method.The uniaxial compression test and biaxial shear test are carried out respectively to study the effects of fracture’s geometry on the strength and failure of rock mass models.The results show that the pattern,inclination,and roughness of the structural plane will significantly change the initiation and propagation mode of new cracks and affect the model’s deformation performance,peak strength,and residual strength.Mechanical test results of the 3D printing rock mass model are very close to that of natural rock mass samples.(3)Size effect of 3D printed rock mass modelCylindrical rock mass models with a built-in major fracture and slab rock mass models with fracture networks are produced by the 3D printing method—the fracture size changes in proportion to the apparent size of the model.The mechanic test reveals the influence of the model size on the strength,elastic modulus,failure mode,and other parameters.And the strength size effect formula of discontinuous rock mass is obtained.Based on rock mass’ s heterogeneity and damage theory,the mesoscopic size effect of discontinuous rock mass is analyzed.And the impact of structure planes on the model size effect is analyzed from the macro point of view.(4)Size effect of 3D printed surrounding rock modelsDeformation and instability processes of 3D printed cavern models with different sizes are studied by physical simulation method and numerical simulation method considering the heterogeneity of rock mass.The results show that with the increase of the size,the strength,deformability,failure mode and energy evolution process of the cavern models behaviour size effects.With increasing the size of the model and structural plane,the reduction ratio of overall strength,energy storage and deformation capacity of the surrounding rock is significantly more potent.According to the above results,the mesoscopic size effect of material heterogeneity and the macro size effect of discontinuous structure in the geological models is determined.(5)Size effect of fractured surrounding rock in Jinping underground tunnelsTaking the intersection of underground laboratory and 3# construction nodes of diversion tunnel in Jinping Hydropower Station as the research object,geological disaster phenomenon of tunnel intersection is researched by geological survey,physical simulation,and numerical simulation.The results show that the failure modes of tunnels with different sizes and under similar environments are different.The tunnel instability mode,deformation process,failure phenomenon of surrounding rock and plastic zone distribution all have noticeable size effects.