Macro- And Micro-fracture Damage Characteristics Of Granite And Its Application In Tunnel Engineerin

In recent years,with the continuous construction of underground engineering in water conservancy and transportation in China,more and more underground engineering has been destabilized and destroyed in the construction process.Granite is a common rock type in the construction process of tunnel,underground chamber,dam and other rock structure engineering.The mineral composition of granite in different areas is generally different,and the mineral mechanical properties are also non-uniform.Therefore,according to the difference of granite mineral composition and the non-uniformity of mineral mechanical properties,the qualitative analysis of granite in a certain area is of great significance for the study of the stability of underground engineering in this area.Based on laboratory mechanical tests and X-ray diffraction tests,the FLAC3D-PFC3 D coupled three-dimensional simulation model of granite is established to study the macro and micro fracture damage and energy accumulation and dissipation laws of granite numerical models under different confining pressures,and the failure criterion of rock considering confining pressures based on energy is derived.Combined with the actual project,the FLAC3 D tunnel numerical model is established to verify the failure criterion of rock.Based on the above research,the Fl AC3D-PFC3 D coupling tunnel numerical model is established to analyze the macro and meso fracture damage of tunnel surrounding rock.The main work and conclusions of the research are as follows:(1)A three-dimensional coupled numerical model is established based on the mineral composition of granite,and the sensitivity analysis of the discrete element’s mesoscopic parameters is carried out,and the mesoscopic parameters of the numerical model of granite are calibrated in combination with the laboratory mechanical test.Through the uniaxial compression test of the numerical model of granite,it can be found that at about 65% of the peak strength of the sample,internal cracks begin to occur and develop rapidly along the weak strength of kaolinite and mica particles,and gradually form the main through X-type cracks from one corner to the opposite corner of the sample and some complex secondary cracks.(2)Through the analysis of the macro and mesoscopic fracture damage characteristics of granite under different confining pressures,the failure process of granite under different confining pressures is similar.The increase of confining pressure will enhance the ability of granite to resist failure,and the increase of confining pressure will change the rock failure form from brittle failure to plastic failure.With the increase of confining pressure,the number of internal bonding failure increases.The proportion of tensile crack decreases gradually,while the proportion of shear crack increases gradually.The rock failure shows obvious shear failure.The unstable development stage of specimen crack is delayed with the increase of confining pressure,which inhibits the damage and failure process of granite.(3)Combined with the characteristics of energy accumulation and loss under different confining pressures,the energy values of each characteristic stress point were extracted,and the eigenvalue functions of elastic deformation energy and dissipated deformation energy were obtained through fitting.It was concluded that the incremental influence of confining pressure on the density of elastic deformation energy of rock was greater than the dissipated deformation energy.According to the law of energy change,combined with the formula of elastic deformation energy accumulated inside rock units,The damage failure coefficient based on energy is derived and used as the failure criterion of granite.(4)In the engineering application study,the FISH language built in FLAC3 D was compiled to extract the calculated data of each unit in the FLAC3 D model,and the rock damage coefficient was brought into the numerical model of FLAC3 D to obtain the damage cloud map of tunnel surrounding rock.The results show that the arch and invert of the tunnel are relatively safe,and the spinner,side wall and arch foot are more damaged.By comparing the damage nephogram of tunnel surrounding rock with the plastic zone of surrounding rock,it is proved that the failure criterion of granite can predict the surrounding rock damage more safely.And it can better show the damage degree and range of tunnel surrounding rock.(5)The tunnel numerical model is established based on the continuous-discontinuous coupling numerical simulation method,and the macro and meso fracture damage of tunnel surrounding rock is analyzed.The research shows that after the tunnel is excavated with the core soil retained by the step method,the bonding damage of tunnel surrounding rock will first occur around the weak kaolinite and mica particles near the tunnel free surface.And along the tunnel spandrel and foot to the depth of the surrounding rock.FLAC3D-PFC3 D coupling can better simulate the non-uniformity characteristics of rock and show the macro and meso structural damage of surrounding rock.Finally,by comparing the two numerical simulation results,it is found that the deformation and damage areas of the two numerical simulation methods are similar,which verifies the accuracy of the coupling of FLAC3D-PFC3 D,and verifies the rationality of the numerical simulation results according to the dynamic disaster of water gusher in the surrounding rock of the tunnel construction site.