Numerical Simulation Study On Thermal Cracking Law Of Granite Under Thermal Coupling

With the rapid development of the economy,resources such as traditional coal and oil tend to be exhausted,and at the same time bring huge ecological problems.In order to achieve sustainable development,it is urgent to find green alternative energy.The abundant geothermal resources are green renewable energy and will be the source of future social development.The study of mechanical properties and thermal cracking mechanism of granite under high temperature and high pressure will greatly guide the development of high temperature geothermal.The thermal rupture nature of granite is due to the different thermal expansion coefficients of diagenetic components.When the temperature rises,the thermal expansion and deformation of different component particles are different,but within the rock mass,any component particles cannot expand and deform according to their own thermal expansion coefficient.After being heated,the component particles are subjected to extrusion or stretching of the surrounding particles,thereby generating thermal stress,and because the cementation material between the components is weak,thermal stress tends to accumulate here,first causing cracking.Limited by the current technical conditions,it is impossible to make real-time and effective observation of thermal cracking inside rock mass under high temperature and high pressure environment.Therefore,numerical simulation has become an indispensable means for thermal cracking research.On the basis of summarizing the previous numerical simulation studies,inorder to reasonably characterize the heterogeneity of granite,which is caused by the random distribution of particles of different diagenetic components in space,the use of digital image processing technology to construct granite-based The two-dimensional PFC particle flow model of surface mesoscopic component distribution was compared with the indoor standard uniaxial compression test to complete the parameter calibration of the PFC model.With reference to the granite permeability measurement test and acoustic emission collection test under high temperature three-dimensional stress,the numerical simulation of thermal cracking of granite is completed.The stress state and temperature rise process are consistent with the test.By comparing with the test results,the correctness of this numerical simulation method is preliminarily proved.The main conclusions of this paper are as follows:(1)Constructing a two-dimensional granite model based on digital image technology can accurately characterize the particle size and spatial distribution of granite diagenetic minerals,and provide a new method for rationally characterizing the heterogeneity of granite and other geomaterials.(2)The indoor standard uniaxial compression test was carried out,and the "trial and error method" was used to calibrate the model according to the test results.The various microscopic particle contact parameters required for the test of the number of times were obtained,and the values were completed.The construction of the mechanical properties of the model.(3)There are two threshold temperature intervals for thermal cracking of granite,one is 170-230?,the other is about 370?,especially around 370?,and thermal cracking occurs sharply.The thermal cracking of granite before100? develops slowly,and the first threshold temperature interval is related to the heterogeneity of granite.(4)The thermal rupture mainly occurs in the quartz-mica andquartz-feldspar boundaries,and the damage is more serious at the boundary of the rock mass;the heterogeneity of the rock mass greatly promotes the thermal rupture;the thermal rupture of the granite under stress state,As the stress difference between the applied axial pressure and the horizontal pressure increases,the proportion of shear failure at the time of thermal cracking increases accordingly.(5)The thermal cracking of granite starts from the boundary of the component.At 430 ?,irregular closed cracks surrounding the component agglomerates have been formed,and some components have a transgranular crack,which is consistent with the experimental results of the thermal fracture of granite by CT observation.