Mechanical Properties Of Granite After Heating-cooling Cycles

In the process of geothermal mining,due to the injection of cold water and the elimination of water vapor,the dry and hot rock mass has undergone multiple heating-cooling cycles.The heating-cooling cycle causes changes in the pore and micro-fracture structure of the dry and hot rock,which in turn causes damage to the internal structure of the dry and hot rock and changes in mechanical properties.In this paper,a combination of laboratory experiments and theoretical analysis is used to systematically study the mechanical properties,acoustic emission response characteristics,ultrasonic response characteristics,damage evolution equations and microstructure evolution laws of heating-cooling granite.The main results obtained through research are as follows:(1)The influence of temperature and cycle number on the stress-strain behavior,capacity expansion parameters,acoustic emission response characteristics and uniaxial compressive strength of granite in heating-cooling cycles were studied by uniaxial compression test and acoustic emission monitoring test.The relationship was established between the temperature and the number of cycles with uniaxial compressive strength of granite in heating-cooling cycles.We advanced a model for the coupling effect of the temperature and the number of cycles on the uniaxial compressive strength of granite in heating-cooling cycles.After applying the ratio of the uniaxial compressive strength of granite to the residual stress after the heating-cooling cycles,we obtained the brittleness index.The brittle-transformation mechanism of granite after heating-cooling cycles was revealed.(2)Using rock damage mechanics,continuum mechanics and thermodynamics theory,by way of phenomenological damage mechanics research methods,we analyzed the influence of temperature and cycle times on the elastic modulus.and obtained the relationship between the elastic modulus of the granite and the damage variable after the heating-cooling cycle.From these,we constructed the constitutive equation of granite damage evolution after heating-cooling cycles.(3)With the help of ultrasonic detector,the ultrasonic response characteristics of heating-cooling cycle granite were studied.The influence of temperature and cycle number on the heating-cooling cycles granite ultrasonic pulse velocity was analyzed.Based on these,we proposed a model that used ultrasonic pulse velocity to predict the uniaxial compressive strength of granite after heating-cooling cycles.(4)By using scanning electron microscope technology,we studied the evolution of the microstructure of granite after heating-cooling cycles.Through using X-ray diffractometer tester to test the mineral composition of granite,we studied the mineral composition change of granite and the evolution of diffraction characteristics.The variation of the maximum diffraction intensity and diffraction angle of quartz with temperature and the number of cycles jointly reveal the influence mechanism of granite mechanical properties after heating-cooling cycles.There are 36 figures,24 tables and 114 references in this thesis.