Research On Macro And Mesoscopic Failure And Energy Evolution Law Of Heterogeneous Granite

The demand for various types of underground space engineering construction in the world is increasing.Especially in recent years,the construction of water conservancy,transportation and other underground infrastructure in China has been carried out,and the engineering problems related to rock are also becoming more complex and diverse.Rock is the main research object of underground space construction.Due to natural geological movement,natural weathering and erosion,there are great differences in mechanical properties and mineral composition of rock.As a typical landform,granite often presents discontinuous structural distribution in the rock,and the composition of micro-mineral particles also has great heterogeneity.The discrete distribution form of granite structure and the random distribution characteristics of minerals are particularly critical to the stability of surrounding rock of underground caverns.The deformation and failure laws are often dominated by these factors.Therefore,it is of great significance to study the mineral composition of the internal microstructure of the rock.In this paper,the macro-meso deformation and fracture law and energy evolution characteristics of granite are studied by means of laboratory test and numerical simulation.The main work and conclusions are as follows:(1)Five mineral types of engineering rock mass were qualitatively obtained based on XRD diffraction scanning test:quartz,potash feldspar,albite,kaolinite and illite.The specific contents of five mineral components were quantitatively obtained by analyzing the X-ray diffraction pattern.The uniaxial indoor compression test was used to obtain the fracture law of granite,which was dominated by shear failure and supplemented by local tensile failure.The microstructure characteristics of granite were determined by scanning electron microscopy(SEM):tensile fracture,shear fracture and tensile-shear composite fracture.It was pointed out that the microscopic fracture of rock was largely dependent on the distribution of weak mineral particles,and the analysis of the scanning results showed that illite was a weak mineral type.(2)Based on the mineral species obtained by XRD ray diffraction results,a discrete element non-uniformity numerical model was built,and the FISH language built in PFC was used to control the random distribution characteristics of various mineral particles in granite.The mechanical parameters were fine-tuned to parameterize the numerical model of the heterogeneous granite,and the macroscopic failure and stress-strain curves of the indoor uniaxial test were verified by multiple conditions,and the numerical simulation was highly consistent with the results of the indoor mechanical test.(3)The macroscopic and microscopic failure characteristics of heterogeneous granite under different confining pressures are studied by numerical model.It is found that the macroscopic failure is mainly tensile-shear consistent failure,and the microscopic failure is mainly slip failure along mineral particles and shear failure through mineral particles.Combined with the peak stress and energy accumulation and dissipation characteristics of specimens,it is considered that the failure of inhomogeneous granite is due to the shear failure of through mineral particles between illite minerals,resulting in the extension of meso-cracks generated by illite to other minerals.The meso-fracture mode of the non-uniformity model under different confining pressures is similar to that under 0 MPa confining pressure,but the confining pressure can improve the overall strength of the specimen and increase the number of cracks.At the same time,the confining pressure condition has a certain effect on the strength of the,enhanced mineral particles‘and a certain effect on the strength of the,weakened mineral particles‘.(4)The energy evolution law of the failure process of the inhomogeneous granite model was explored.Under different confining pressures,the energy evolution trend showed a“micro-growth–slow growth–sharp differentiation”mode.The energy evolution curves of various mineral conditions were similar.The sharp differentiation of energy mainly occurred in the overall failure stage of the rock,which was manifested as the decrease of the elastic strain energy and the total energy mutation,and the growth rate of the dissipative energy showed a sharp growth evolution.The energy value of,enhanced mineral particles‘increases proportionally with the increase of the content,and the energy value of,weakened mineral particles‘decreases inversely proportionally with the increase of the content,and the representation of this phenomenon becomes more obvious under the higher confining pressure.(5)Based on the full stress-strain curve of the numerical model of inhomogeneous granite,the energy damage criterion indexes w₁ and w₂ are derived,and the critical early warning curves of energy damage criterion indexes under different confining pressures are fitted.The non-uniform discrete element numerical modeling was established for the surrounding rock of Dagangshan Tunnel(the rock acquisition engineering section of laboratory test)on the Lushi Expressway,and the failure and damage of surrounding rock excavation under the condition of actual mineral composition in the project were analyzed.The macro-micro damage of surrounding rock and the damage assessment of w₁ and w₂ indexes under different mineral conditions were compared.