Research On Creep Model For Cohesion Weakening Friction Strengthening Of Deep Granite And Micro-Failure Mechanism

Rocks in nature are affected by long-term complex physical and geological environment,and show complex characteristics such as heterogeneity and discontinuity.Because of the limitation of technical means,it is difficult to analyze the complex mechanical characteristics of large-scale surrounding rock excavation directly in the study of geotechnical engineering.How to construct a numerical method of a large-scale fine model that can characterize the rheological properties of different types of rocks,it is of great significance to analyze and predict the meso-rheological fracture characteristics and local fracture law of deep wall rock under high stress condition.In this paper,the uniaxial compressive strength test of prefabricated fractured granite and the creep test of intact granite under different confining pressures are carried out by taking core samples from the working face at-1380 m in Xincheng Gold Mine,Shandong Province.The creep curves of granite Stress–strain curve under different confining pressures were obtained,and the failure patterns of the specimens were recorded,the law of crack propagation,fracture characteristics and creep behavior of granite specimens with different crack dip angle and rock bridge dip angle are studied.Combined with particle flow software,the excavation process of surrounding rock under high stress is simulated,and the model of surrounding rock on engineering scale is constructed by using the parameters obtained from laboratory tests,and the local failure evolution process is studied:(1)The in-situ stress of the tunnel at the-1380 m level face of Xincheng gold mine in Shandong province was measured,and the axial and lateral wall rock pressures were obtained.The observation records the local deformation and failure forms of the surrounding rock after excavation for three months.The main failure modes of the surrounding rock are shear slip at the vault and plate fracture along the side wall.(2)The Stress–strain curve and fracture patterns of intact and fractured granite samples obtained from laboratory tests were studied to obtain the conventional mechanical parameters of the samples,the creep process of intact granite is studied by means of graded loading,and its creep characteristics and parameters are obtained.(3)Based on the principle of the bond degradation-friction strengthening model and the parameters obtained from laboratory tests,the influence of the stress state on the bond parameters was studied.Considering the difference of creep strain rate between numerical simulation and laboratory test under high stress and combining with stress corrosion model,a bond degradation creep model is proposed.Compared with the conventional stress corrosion model,the creep curves obtained by numerical calculation are more consistent with the experimental results.(4)Based on the ratio cluster method of controllable radius,the particle flow model is constructed,and the characteristics of local failure and crack evolution of surrounding rock affected by time effect are simulated by the sampling method of particle decline,the variation process of surrounding rock parameters is realized by measuring circles of different sizes and attenuation ranges,and the fracture forms are compared with those in engineering practice,the proposed method can effectively predict the local failure form of surrounding rock after excavation for a period of time,and has reference value for similar projects.