Experimental Study On Thermal Damage Mechanism And Mechanical Properties Of Rock

Rock is a structure composed of one or more mineral components,contains many microcracks and microporous holes and has anisotropic physical and mechanical properties,in the development of geothermal resources and the deep disposal of nuclear waste,the mechanical properties of rocks are often affected by temperature.In this paper,the Shaanxi Huashan granite is selected as the research object,and a series of experimental studies are carried out on granite samples treated with different temperatures.The mechanical behavior,the mesoscopic mechanism and the acoustic emission characteristics are discussed,the main research work and conclusions are as follows:First,the stress-strain response of granite at different temperatures and the variation trend of the mechanical parameters with the temperature were studied by uniaxial and triaxial compres.At the same time,the mineral composition of granite after temperature was analyzed by X-ray diffraction test.The results show that the granite at normal temperature is gray white,and gradually becomes warm hue with the increase of temperature,the brittleness and volume are increased at same time;Within the same temperature range,the compressive strength under triaxial compression is much greater than that under uniaxial compressive strength,and the effect of confining pressure on improving strength is more obvious with increasing temperature;The X-ray diffraction curve shows that the diffraction information of the main composition of the rock samples is not obviously changed when it is below500?,after 500?,the diffraction peak of quartz decreases obviously in the range of26.5°~ 27.0°diffraction angle.Then,ultrasonic testing of granite samples after the temperature of 20,300,500,700 and 900 degrees centigrade was carried out.The thermal damage characteristics of rock are investigated through the change of wave velocity and form,at the same time the microscopic observation of rock temperature damage was observed with the aid of scanning electron microscope.The study found that when the temperature is below500 ?,the velocity of longitudinal wave decreases slowly with the increase of temperature.When the temperature is above 500 ?,due to the phase transition of quartz in granite,the velocity of the longitudinal wave rapidly decreases;After 700?,the damage of rock samples is serious,and the attenuation of wave velocity is gradual;The scanning electron microscope image shows that with the increase of temperature,the number of cracks increases.Finally,the AE energy count in real time temperature and post time temperature are compared with the uniaxial compression and acoustic emission test,and the shape of the stress-strain curve,the peak stress,the peak strain,the modulus of elasticity and the failure mode are discussed.The results show that the higher the temperature,the more cracks in the interior of the granite,as weill as the more significant the internal damage and acoustic emission activity;After the same heat treatment,the plastic stage of the real time temperature is more obvious,the peak strain is larger,the peak stress and the modulus of elasticity are smaller,The main reason is that the thermal stress effect of granite under temperature is obvious,and the internal crack part healing after temperature leads to the increase of rock sample stiffness.