Researche On Deformation Characteristics Test And Micromechanical Analysis Of Rock At High Temperature Treatment

The construction and repair of Geotechnical engineering,such as deep mining,geothermal resources development,the disposal of nuclear waste,underground cavern and tunnels fires.These projects are related to the impact of high temperature.The deformation behavior of rock and rock structure will change after thermal treatment and it's unrecoverable,which has a significant impact on the stress field of underground rock mass and structural safety of underground engineering.Combined with the impact of groundwater,rock mass in the effect of coupled thermo-mechanical-hydro,which damage degradation degree increased.This may even damage the ecological environment.This study aims to investigate the macro-deformation behavior,damage evolution process,and failure characteristics of thermal treatment Beishan granite in Ganshu Province,a potential site for China's HLW disposal.Therefore,triaxial compression tests coupled with transmitted cross-polarized light and XRD micro-observation under different confining stress were performed on Beishan granite samples.Based on lab test results on rock,by considering the effect of rock crack micromechanical damage model,damage evolution mechanism of Beishan granite in the compression process is further studied.In this paper,the research results are as follows:?1?Before 400?,rock's apparent morphology has no obvious change.With the rising of the temperature,sample color deepened gradually and appeared light brown red when 1000?.The mass,density and P-wave velocity is gradually decreasing,while the volume is slowly rising with the increase of temperature.The macroscopic physical properties were staged feature.Therefore,it can be roughly divided into three stages:?1?room temperature?25??⁴00?stage;?2?400?⁹00?stage;?3?900?¹000?stage.Granite damage threshold temperature is approximately between 400?⁶00?.The internal mineral structural damaged.The critical temperature of macroscopic deformation characteristics is about 800?.?2?Triaxial compression stress-strain curve of heat treatment Beishan granite can be divided into five typical stages:microcrack compaction stage?I?,elastic deformation stage?II?,microcrack stable propagation stage?III?,microcrack unsteady growth stage?IV?and post-peak residual deformation stage?V?.As the temperature increases,brittleness weakened,ductility enhanced and yield point decreased.Post-peak softening stage is more and more obvious,and rock still maintains a certain residual strength after destroyed.Granite peak strength increase at first and then descend with increasing temperature,and reached the maximum at 200?.Peak strain increases.Elastic modulus decreased.To some extent,confining pressure limits the temperature on the granite peak strength,peak strain and elastic modulus of degradation.?3?After thermal treatment,damage variable of granite D_T is gradually increasing with the increase of temperature.But at 200?,damage variable D_T decreased slightly.As the temperature increases,the maximum diffraction intensity of granite minerals first increased and then decreased.The internal structure of the rock is increasingly broken.The cracks development degree is higher and higher,and this change irregularity.Mineral mirror gradually darken.But at 200?,micro-cracks have closed trend.?4?Numerical simulation results show that the micromechanics damage model of anisotropic rock can describe the main mechanical characteristics of thermal damage granite in different confining pressures,which reflects the stress-stain curve of four typical stages before the peak.With temperature increasing,compaction stage gradually extended,crack normal stiffness decreases in linear elastic stage,plastic feature of crack initiation and extension stage enhancement.The sensitivity of the dilatancy angle and the initial damage density is stronger.Crack normal stiffness show stronger sensitivity to compaction stage and linear elastic stage.c₁ has strong sensitivity at?stage,but smaller than dilatancy angle,the initial damage density,crack normal stiffness.?5?At low temperatures and confining stresses,form of failure is tension splitting with multiple axial crack around the destruction surface.At high temperatures and confining stresses,form of failure is steep angle shear failure and relatively intact,which would transform from brittle fracture to plastic steer dip shear deformation as the temperature and confining stress increases.