Meso-scale Numerical Simulation Of Failure Mechanism Of Granite Under Different Stress Paths

Granite is a kind of magmatic rock composed of feldspar,mica and quartz minerals,with high strength,hardness,strong brittle and so on.The granites that occur in the high initial stress field environment are easy to show different forms of yield failure such as sheet gangs and rock bursts under excavation disturbance,which will affect the construction progress and safety.The underground rock excavated in underground caverns undergoes complex loading and unloading processes,and the stress path affects the mechanical properties and failure mechanism of the rock mass,which in turn presents different requirements for support design.Therefore,it is of great significance to study the mechanical properties and failure mechanisms of granite under different stress paths.In this paper,the uniaxial compression test,triaxial compression test and unloading test of granite are mainly carried out.The mechanical properties and failure mechanism of granite under different stress paths are analyzed.Finally,the failure mechanism of granites is revealed.It has certain guiding significance for exploring the mechanism of the destruction of surrounding rock in underground caverns and further improving the stability evaluation method of surrounding rock in underground caverns.The main research work of the thesis is as follows:(1)Using discrete element particle flow numerical simulation software,digital image technology is used to identify and analyze granite digital photos and establish a simulation model that reflects the real mesostructure of granite.Through multiple sets of uniaxial compression simulations that change a single meso-parameter,the sensitivity of mesoscopic parameters is analyzed.Using the indoor uniaxial compression test as reference,the mesoscopic parameters of the granite simulation model were calibrated.Based on the laboratory test method,a numerical test scheme for uniaxial compression test,triaxial compression test,and unloading test was developed.(2)On the basis of the calibration of the parameters,the uniaxial compression test,the triaxial compression test and the unloading test were carried out using discrete element particle flow numerical simulation software,and the mechanical properties of the granite under different stress paths were analyzed.The experimental results show that the granite model established by digital image technology can reproduce indoor test results well.Under the loading and unloading paths,granites all show obvious brittle failure,and they are more likely to be destroyed under the unloading path.Under the unloading path,the cohesion force decreases compared to the loading path,and the internal friction angle increases with the loading path,which shows a strong lateral expansion damage.(3)Analyze the damage mechanism of granite under different stress paths according to the indoor test and numerical simulation results.In the uniaxial test,the failure of the rock sample is the fracture of the macro-crack almost perpendicular to the axial,and the distribution of the crack is more concentrated.When the confining pressure is low,the failure of the rock sample in the triaxial compression test is mainly single-shear failure,and with the confining pressure increasing,it gradually develops into an “X”-shaped conjugate shear failure.The unloading test is dominated by splitting and shearing failure,showing a strong lateral expansion damage,and the unloading rate,confining pressure,unloading point,and unloading path have different degrees of influence on the damage morphology.