Investigation Of Deep Excavation-Induced Fracture,Large Displacement Of Soft Surrounding Rock Under High Situ-stress And Grouting Reinforcement Of The Rock

In deep underground engineering,as a result of high in-situ stress,low strength of surrounding rocks and the effect of the underground water and thermal field,the large deformation of the surrounding rocks typically occurs due to the seriously broken of the surrounding rocks.Consequently,not only the serviceability,durability of the engineering is reduced,but also the safety of the workmen and equipments is threatened.As an effective measure in treatment of this problem,grouting could improve the integrity,stiffness and strength of the surrounding rocks through improving the mechanical properties of the rock joints.The current research of grouting technology is focused on the rheological property and flow rule in the crack network of surrounding rocks,while the research of the strength of grouted rock joints with random morphologies is limited still.The improvement of the joint strength due to grouting could improve the mechanical response of the surrounding rocks,and evaluate the reinforcement effect of the grouted surrounding rocks.The mechanical response of the surrounding rocks is controlled by the displacement of the joints and rocks and the broken of the rocks,and it is a nonhomogeneous,discontinuum and large deformation mechanical processes.The traditional theoretical solution and laboratory tests are unable to quantify this process.The hybrid finite-discrete element method(FDEM)have recently emerged in the field of rock mecahnics as simulation tools for fractruring processed in rocks and rock massed,which can modelling the fracturing process,large deformation of the deep underground surrounding rocks before and after grouting.Based on the laboratory experiments,theoretical analysis and numerical simulation,the main contents of this dissertation are briefly introduced as below.(1)The improvement of the shear and tensile strength of grouted sandstone and mudstone joints due to ordinary cement,superfine cement with different water-cement ratio(w/c),epoxy resin and polyurethane is studied through the direct shear test of grouted joints.The experimental results show that,the shear strength of the sandstone joints could be reduced by the cement grouting when the w/c and the normal stress are high;the shear strength of the mudstone joints could be improved significantly when the s/c is low.Epoxy resin could bond with the two types of rock perfectly,and could improves the shear strength of the joints to the strength of the intact rock.(2)Based on the continuum micromechanical approach,the elastic properties of hardened cement paste with high w/c is studied.Taking the micro morphology of rock joints and the interfacial transition zone into consideration,the micro shear fracture mechanism of the interface of the groute and the rock is studied,and the micro shear fracture model without consideration of the macro joint roughness is proposed.Furthermore,the peak shear strength moel apply to general grouted joints is proposed,which considering the macro joint roughness.(3)The FDEM codes of Munjiza are improved,and the parallel version based on Compute Unified Device Architecture is developed.The computational efficiency of FDEM is highly improved,and this make it possible to solving complex large-scale engineering computation problems.(4)Based on the parallel computation codes,the micro and macro fracture process of rock under uniaxial compression is simulated,and the results show that,the macro fracture is caused by the propagation,merging and interaction of the micro shear and micro tensile fracture.The direct shear test of intact rocks,grouted and ungoruted joints is simulated,in which the degradation and fracture of the asperities could be reproduced,and the results show that,the asperities crush degree increase as the normal stress increase.However,the simulation of the joint three-dimensinal mechanical response though two-dimensional method could not perfectly capture the post-peak mechanical properties.The simulation results of peak strength of uniaxial compression and direct shear are in good agreement with the theoretical solutions.(5)The Immediate fracture process and the long term frcture process of surrounding rocks in deep underground engineering is simulated,in the latter the time effect of the rock and joints strength is taken into consideration.Considering the improvement of joint strength due to the grouts,the effect of grouting at different stage in long term fracture on the fracture and displacement of surrounding rocks is studied,in order to obtain rational grouting time.