Experimental Study On Physical And Mechanical Properties Of Granite After High Temperature-water Cooling Cycle

In this paper,in the hot dry rock geothermal development,the rock circulation high temperature and the water cooling problem are selected as the research background.The representative granite from the dry hot rock was selected and subjected to high-temperaturewater-cooled cycling at different temperatures in the laboratory,and the static uniaxial compression test and the static Brazilian splitting test were conducted on the granite after cycling using a universal testing machines.The effects of different temperatures and different number of high temperature-water cooling cycles on the physical and mechanical properties of granite such as density,saturation water absorption,longitudinal wave velocity,compressive strength and tensile strength were analyzed,and the damage deterioration mechanism of granite after high temperature-water cooling cycles is explored by analyzing the macroscopic fragmentation mode and fine damage of granite,and the following conclusions were drawn:(1)It was found that the appearance of granite was greatly changed by the effect of high temperature.Yellow spots appeared on the surface of specimens at 400?,and the surface of specimens gradually turned white at 600?.When the temperature is higher than 400?,micro-cracks begin to appear on the surface of the specimen,and with increase of the number of cycles,the cracks become wider and deeper.At 600?,the edge of the rock sample is broken.(2)The increase in temperature and the number of high-temperature-water-cooling cycles caused the physical and mechanical properties of granite such as mass,density,saturated water absorption,longitudinal wave velocity,compressive strength,tensile strength,elastic modulus and tensile modulus to be degraded to different degrees.And a high correlation was found between the physical property parameters and mechanical property parameters.The longitudinal wave velocity and the saturated water absorption show a linear increasing relationship,and the compressive strength and the tensile strength show a linear decreasing relationship.(3)Observing the failure of granite samples under uniaxial compression,it is found that with the increase of temperature and the number of high temperature-water cooling cycles,the failure mode of granite will experience three failure modes: tension split failure,oblique shear failure,and cone shear failure.Through the screening experiment,it is found that the rock damage is more broken with the increase of temperature,the surface cracks gradually increased and the tree-like cracks appear.(4)Through ultrasonic test and SEM(scanning electron microscope)scanning the granite treated by high temperature and water cooling,found that the increase of the temperature reduces the flatness of the granite surface structure and the degree of cementation between particles.As the number of high temperature-water cooling cycles increases,the surface microcracks gradually appear,and gradually widened and deepened.The increase of pores made the waveform of the granite gradually sparse and disordered,indicating that the internal structure of the granite was greatly damaged.(5)The damage variable of granite increases with the increase of temperature and the number of high temperature-water cooling cycles,which were fitted with linear fitting function and cubic polynomial respectively,and the fitting results were better.The increase of damage variable indicates that the damage degree of granite increase with temperature and the number of high temperature-water cooling cycles,and the influence of temperature is more serious.