Study On Penetration And Deformation Of Coarse Particle Granite Under High Temperature And Triaxial Stresses

The development of high quality hot dry rock geothermal resources involves the penetration and deformation of pore-fractured rock masses at high temperature.In the enhanced geothermal system,the heat transfer efficiency of artificial thermal reservoir was directly determined by its permeability of bedrock,and deformation generated by thermal reservoir during the temperature rise and fall may cause surface ground to lift or subside,besides,with the depth of wellbore increases,temperature becomes higher and higher,which makes drilling and maintenance more difficult.Based on the background of hot dry rock geothermal exploitation,this paper analyzes the penetration properties and deformation characteristics of granite at high temperature and triaxial stresses,find the Mohr-coulomb failure criterion of granite at real-time high temperature and high pressure by mechanical loading experiment,following primary conclusions are summarized:(1)Hydrostatic stress has obvious inhibiting effect on penetration and thermal deformation of granite,the larger hydrostatic stress,the more obvious suppression effect.For permeability,with the hydrostatic stress rises,peak value,initial value and multiple relationship of peak value to initial value are all decreases,but both the temperature of initial permeability and peak permeability are increases;meanwhile,with hydrostatic stress rises,both the amount of expansion deformation and coefficient of thermal expansion of granite are decreased while threshold temperature of thermal deformation increasing with hydrostatic stress rising.(2)The suppression effects of external loading on permeability and thermal deformation of granite are quantitatively described by parameters,simultaneously,factor of temperature was also considered.(3)In a single thermal cycle,the amount of compressive deformation of granite in the cooling stage greater than the amount of expansion deformation in heating stage,this gap value is reducing with the increase of thermal cyclic times;with the increasing thermal cyclic times,threshold temperature of thermal deformation is also increase,and deformation in cooling stage gradually changes from ahead of temperature to lag behind of temperature.(4)With confining pressure rises,peak strength,elastic modulus and post-peak deformation modulus of granite are all increased linearly,mechanical properties of rock mass were enhanced obvious,the evolution law of peak strength and peak strain of granite with temperature in loading stage were conformed second-order polynomial function form,under the coupling effect of temperature and stress field,evolution of mechanical properties of granite with temperature are tend to be complexity,no longer vary monotonically like the condition of confining pressure affect.(5)It is verified that the Mohr-Coulomb strength criterion has good adaptability to this research work.Introduce the function form of the Mohr-Coulomb strength creterion to induce the strength criterion of granite,and both temperature and stress field are take into account,the result is shown as equation 5-18,the mechanical parameters which in accordance with this analytical formula vary with temperature are basically consistent with the results of real time experimental measured.