Study On The Triaxial Mechanical Properties And Particle Flow Simulation Of Granites With Different Grain Size After High Temperature

Deep underground resource development and space utilization both involve complex underground engineering issues,such as deep underground storage of nuclear waste,geothermal resource extraction,deep coal resource extraction and coal bed methane gas extraction,and subsea oil drilling.In these underground projects,the mineral and structural composition,physical and mechanical properties of rocks are different,and these rocks are often in different in-situ stress and different temperature environments,which will have a very important influence on the long-term stability of rock engineering.For example,in the deep geological storage of nuclear waste,granite with different particle size composition will undergo corresponding changes in physical and mechanical properties due to the heat generated by nuclear waste decay for a long time,and this will affect the stability and safety of nuclear waste storage during tens of thousands of years of service,so it is highly significant to study the physical and mechanical properties of granite with different particle size under different temperature and stress environments.In view of this,in accordance with the combination method of laboratory testing and numerical simulation,using advanced testing equipment and related testing techniques,this thesis studied the physical and mechanical properties of fine-grained and coarse-grained granite at room temperature and after high-temperature treatment,and analyzed the mechanism of high temperature action from the microstructure in detail.The main research contents and results of this thesis are as follows:?1?The conventional triaxial compression tests and the Brazilian splitting tests of fine-grained and coarse-grained granite at room temperature were carried out,and the triaxial compression stress-strain curve and tensile stress-displacement curve of the specimen,as well as the strength and deformation parameters and failure mode of the specimen were obtained.Moreover,from the perspective of confining pressure and particle size,its influence on the characteristics of the sample curve,the strength and deformation parameters and the failure mode were analyzed.The results show:that the mechanical parameters of fine-grained granite,showing better mechanical properties,are higher than those of coarse-grained granite;that under low confining pressure??₃?12MPa?,the deformation parameters of fine-grained granite are higher than those of coarse-grained granite,while under high confining pressure??₃>12MPa?,the deformation parameters of the them are not much different;that the existence of confining pressure effectively closed the pores and cracks inside the sample,and improved the deformation parameters of the sample.?2?In view of the influence of temperature and confining pressure on the mechanical deformation characteristics of rocks in high-temperature underground projects,the uniaxial compression tests,triaxial compression tests and tensile splitting tests of fine-grained and coarse-grained granite after different high-temperature treatment were carried out.After that,we analyzed the physical properties of the granite samples,as well as the influence of temperature and confining pressure on the strength parameters,deformation characteristics and fracture modes of granite with different particle size,and a qualitative and quantitative relationship were obtained.Meanwhile,the microscopic mechanism analysis of high temperature effect was studied.The results show:that under the same confining pressure,the triaxial compressive strength and the triaxial compressive crack damage threshold of the specimen increase first and then decrease with the increase of temperature,and the threshold temperature is 200?;the structural integrity of the sample is continuously destroyed with the increase of temperature,and the higher the temperature is,the higher the degree of thermal damage of the sample is.?3?Based on the results of conventional triaxial compression laboratory tests on granite with different particle size,this thesis constructed the particle numerical model of fine-grained and coarse-grained granite and obtained the quantitative relationship between meso-parameters and macro-mechanical parameters by using PFC 2D discrete particle flow program and its parallel bonding model.In addition,the strength and deformation characteristics and failure characteristics of the sample were simulated,and the mesoscopic mechanism analysis was carried out from the perspective of the mesoscopic crack growth,mesoscopic displacement field and mesoscopic stress field of the sample.The results show that the numerical simulation test results are highly consistent with the laboratory test results,and the mesoscopic mechanism analysis also clarifies the triaxial compression damage fracture mechanism.There are 87 figures,14 tables and 126 references in this thesis.