Study On Mechanical Properties And Acoustic Emission Law Of Sandstone After High Temperature

The geological environment of deep underground geotechnical engineering such as underground coal gasification(UCG),geothermal energy exploitation and the disposal of highly radioactive nuclear waste will be affected by high temperature.When the rock is subjected to high temperature,it causes thermal damage and changes the physical and mechanical properties of rock.Therefore,it is of great theoretical significance for deep geothermal mining,construction safety and stability of underground geotechnical engineering to study the physical and mechanical properties of rocks after high temperature.Uniaxial compression test and acoustic emission monitoring are carried out on sandstone treated by different temperature,heating rate,high temperature duration and cooling method,and the physical and mechanical properties,acoustic emission characteristics and energy evolution are studied in the paper.The main contents and results are as follows:(1)The basic physical properties of sandstone under different temperature,heating rate,high temperature duration and cooling method were tested.The results show that the mass loss rate,volume increase rate,density decrease rate and P wave velocity decrease rate of sandstone increase with the increase of temperature.The mass loss rate of sandstone remain constant with the increase of heating rate at 350?,while it shows the trend of decrease at 950?,the volume increase rate,density decrease rate and P wave velocity decrease rate of sandstone show the trend of decrease with the increase of heating rate at 350? and 950?.The mass loss rate,volume increase rate,density decrease rate and P wave velocity decrease rate of sandstone increase with the increase of high temperature duration at 350? and 950?.The mass loss rate,volume increase rate and density decrease rate of sandstone remain unchanged under different cooling methods,but P wave velocity decrease rate is greater under water cooling.(2)The uniaxial compression tests of sandstone under different temperature,heating rate,high temperature duration and cooling method were carried out.The mechanical characteristics of sandstone were analyzed.The results show that peak strength doesn't change much when the temperature doesn't exceed 800?,but decreases suddenly at950?,and the elastic modulus decreases with the increase of temperature.The peak strength and elastic modulus show the trend of increase with the increase of heating rate at 350?,while at 950?,the peak strength and elastic modulus first increase and then constant.The peak strength and elastic modulus first decrease and then remain unchanged with the increase of high temperature duration at 350?,while at 950?,the peak strength and elastic modulus show the trend of decrease.The peak strength and elastic modulus of sandstone cooled by water are lower than those by natural cooling.(3)The uniaxial compression tests of sandstone under different temperature,heating rate,high temperature duration and cooling method were carried out,and AE monitoring was carried out to analyze the variation of AE parameters.The results show that the AE accumulative ringing count increases with the increase of temperature.The AE accumulative ringing count decreases with the increase of heating rate at 350? and950?.The AE accumulative ringing count increases with the increase of high temperature duration at 350? and 950?.The AE accumulative ringing count of sandstone cooled by water is lower than those by natural cooling.(4)The energy evolution law of sandstone under different temperature,heating rate,high temperature duration and cooling method during uniaxial compression is studied.The results show that the total energy required for sandstone failure,the elastic energy storage limit of sandstone and the dissipated energy after failure of sandstone increase with the increase of temperature when the temperature doesn't exceed 800?,and suddenly decrease when the temperature exceeds 800?.The total energy required for sandstone failure,the elastic energy storage limit of sandstone and the dissipated energy after failure of sandstone increase with the increase of heating rate at 350?,while at950?,the total energy required for sandstone failure,the elastic energy storage limit of sandstone and the dissipated energy after failure of sandstone first increase and then decrease with the increase of heating rate.The total energy required for sandstone failure,the elastic energy storage limit of sandstone and the dissipated energy after failure of sandstone increase with the increase of high temperature duration at 350?,while at950?,the total energy required for sandstone failure,the elastic energy storage limit of sandstone and the dissipated energy after failure of sandstone decrease with the increase of high temperature duration.The total energy required for sandstone failure,the elastic energy storage limit of sandstone and the dissipated energy after failure of sandstone under water cooling at 350? are all lower than those under natural cooling.