Study On Mechanical Properties Of Granite After Heating-Cooling Cycles Based On Hot Dry Rock Mining

In order to improve the stability and geothermal development efficiency of hot dry rock in the process of mining,it is very important to carry out the research on the physical and mechanical properties of hot dry rock under the action of different high temperature levels and times of water cooling cycles.Based on granite as the research object,this paper adopts the indoor test and numerical simulation of the combination of research methods,from the macro mesoscopic scales,research reveals the action of granite stress-strain response,macro evolution of mesoscopic cracks and damage mechanism under different high temperature thermal shock and water cooling cycles coupled process.The main achievements are as follows:(1)The degradation mechanism of macroscopic physical and mechanical properties of granite after heating-cooling cycle was revealed from the microscopic point of view by SEM scanning electron microscope and XRD diffraction testing method.The evolution characteristics of micro-crack structure of granite after heating-cooling cycles are illustrated.The variation of the granite mineral composition and its maximum diffraction intensity and diffraction Angle with the response of temperature and number of cycles after heating-cooling cycle are obtained.(2)Based on a large number of indoor uniaxial tests of granite after heating-cooling cycles,the factors affecting the sensitivity of different temperatures and cycles to the uniaxial compressive strength,tensile strength,acoustic emission response and failure mode of granite were revealed.The results show that with the increase of temperature and the number of cycles,the thermal shock damage degree of the sample is higher,and the range is 24.7%-94.3%,and the deterioration of physical and mechanical properties is gradually intensified.(3)Based on high-precision CT scanning and 3D reconstruction,the failure mode and crack evolution law of granite under triaxial compression were obtained.Under the action of different temperatures and cycles,the granite changed from brittle tensile failure to shear-thermal shock damage and crack penetration composite plastic failure.The influence mechanism of different temperatures,cycles and confining pressures on the parameters such as peak strength,circumferential strain,elastic modulus,cohesion and internal friction angle of granite after heating-cooling cycles was revealed by triaxial compression experiments with variable confining pressure.(4)Based on discrete element program PFC2 D,established the parallel bond numerical model of granite sample after heating and cooling,determine the mesoscopic mechanics parameters of the model,from the perspective of mesoscopic recreates the crack distribution and development characteristics of granite after heating and cooling in uniaxial compression process,analyzes the strength and modulus of elasticity mechanics parameters,such as the degradation mechanism of increased with the temperature level.Under the action of temperature,the shear cracks proliferate,resulting in the granitic matrix showing granular distribution characteristics,and the internal bearing structure of the granite significantly deteriorated.There are 74 figures,24 tables and 99 references in this thesis.