Experimental Study On Biot Coefficient Of Granite After Heating And Water-cooling Treatment

During the mining of Hot Dry Rock,the rock is rapidly cooled by water under high temperature conditions.The physical and mechanical properties of granite after heating and water-cooling treatment are studied and analyzed.On the other hand,considering the mining process of geothermal resources,the surrounding rock is in a dynamic equilibrium system of thermal-hydro-mechanical(THM)multi-field coupling.The study of the physical and mechanical properties of rock under THM multi-field coupling condition is the basis for evaluating the safety and stability of surrounding rock.Therefore,the physical and mechanical properties and pore structure of granite after heating and water-cooling treatment are studied.In this thesis,granite after high temperature heating and water-cooling treatment used as research obeject is studied.The physical properties are analyzed from the aspect of pore structure and mineral composition.And the variation of parameters of its physical properties with heat temperature has been discussed(including density,porosity,gas permeability,longitudinal wave velocity,thermal conductivity,mineral content,specific surface area,pore size and distribution);The conventional triaxial compression test is carried out to obtain basic parameters of the mechanical properties of granite after heating and water-cooling treatment(including peak strength,elastic modulus,Poisson's ratio),and the variation of ites mechanical properties with heat temperature has been investigated.At the same time,based on the parameters of its mechanical properties obtained by the conventional triaxial compression test,the Biot's coefficient was introduced to study the deformation characteristics of the internal pores of granite after heating and water cooling treatment.And the influence of stress induced and heating and water-cooling treatment on Biot's coefficient of granite are discussed.The main conclusions are as follows:(1)According to the evolution law of the physical and mechanical properties of granite after heating and water cooling treatment,it can be divided into three stages according to temperature: 25? ~ 200?,200? ~ 500? and above 500?.At range of 25? ~ 200?,the strengthening effect caused by heating and water cooling treatment increases the compactness of the sample and enhances the physical and mechanical properties.At range of 200? ~ 500?,the thermal cracks caused by the heat treatment increases.When the heat treatment temperature is higher than 500?,the thermal decomposition of biotite and the ?-? phase transformation of quartz will cause the volume of mineral particles to increase,which will cause a large number of micro-cracks inside the rock sample to greatly weaken its physical and mechanical properties.(2)It is found that a large number of micro-cracks in the granite generate when it experienced high temperature heat treatment through micoroscopic test(including X-ray diffraction analysis,Analysis on specific surface area and pore,Scanning Electron Micoroscope)which caused an increase in specific surface area,an increase in total pore volume,and no significant change in mineral contet.At the same time,it can be concluded that the content of biotite and quartz is the key to affect the physical and mechanical properties of granite.(3)The axial Biot's coefficient of granite increases with the increase of axial strain,and the lateral Biot's coefficient of granite does not increase that obviously or even decrease with the increase of axial strain.With the increase of confining pressure,the changes of axial and lateral Biot's coefficient are limited by the confining pressure.(4)The relationship between the Biot's coefficient of granite and the temperature of heat treatment is consistent with the evolution of the physical and mechanical properties of granite with temperature.