Experimental Study On Macro And Microscopic Characteristics Of Rocks Under High Temperature

The geological environment which rock engineering such as deepresource extraction, formation of buried high-level radioactive nuclear wastedisposal and the reconstruction of underground engineering are likely toexperience a certain high temperature. Therefore, the strength anddeformation characteristics of rocks under high temperature will be directlyrelated to the design, construction and long-term safety.The mechanical parameters acoustic emission characteristics andmicroscopic structural changes of Linyi granite were studied under hightemperature using advanced laboratory equipment and testing techniques.And we discussed the constitutive equation of granite under hightemperature from the perspective of the disturbed state concept. The mainwork is as follows:(1) The laboratory tests are made for studying on mechanicalcharacteristics of Linyi granite, Shandong at room temperature to800℃using hydraulic-pressure servo testing system MTS810and MTS815. Thevariations of peak stress, peak strain, elastic modulus, stress-strain curve andfailure modes and causes are analyzed at as well as after differenttemperature.(2) The laboratory tests are made for studying characteristics ofacoustic emission(AE) of granite from Linyi in Shandong province at20℃to800℃using hydraulic-pressure servo testing system MTS810andacoustic emission instrument AE21C. The relationship between ringdowncount rate of granite and time as well as the relationship between AE parameters and stress-strain curves due to uniaxial compression loading areanalyzed under different temperatures.(3) A detailed analysis is made to detect the morphology of Xuzhoumarble from room temperature to1400℃using polarizing microscope andcombine it with acoustic emission characteristic parameters from200℃to800℃.(4) Based on the disturbed state concept theory, taking into account theeffects of temperature factors and establish the constitutive model of rockunder the conditions of high temperature.The main results are as follows through the above studies:(1) Studying results have shown that peak strength and elastic modulusdecrease continuously with increasing temperature, while peak strainincreases overall at high temperature. The mechanical index of granite afterhigh temperature decreased significantly with increasing temperature, butgenerally better than that at high-temperature. The failure type of Linyigranite shows distinct brittle failure when temperature is below800℃.(2) Studies have shown that ringdown count rate rises and AE activitybecomes more frequent with temperature increases both in the processes ofheating and loading. AE parameters are quite different at and after the hightemperature. Ringdown cumulative count of granite at high temperature ishigher than that after high temperature. The high temperature causes asignificant increase in energy and accelerating the energy dissipation.(3) Some results are achieved: there are more micro-cracks andmicro-voids and the internal injuries become more serious with increasingtemperature in the heating process. The difference of microscopicmorphology between Marble and granite under high temperature is mainlyreflected in the different crack initiation expansion speeds. There is acorresponding relationship between rock acoustic emission characteristicparameters and its internal crack network formation. The ringing cumulativenumber of rocks increases with temperature increases which indicate that theinternal cracks continue to expand with increasing temperature.(4) Theoretical curves were compared with the experimental curves using the established constitutive model of rock under high temperature. Thetheoretical curves at different temperatures well reflected the constitutiverelations of granite which provides a theoretical basis and reference usingnew methods to explore the constitutive relation of rocks under hightemperature.