Thermo-Mechanical Coupling Test Of Granite Containing Pre-Existing Fissures

Rock mass failure in high temperature environment exists widely in deep rock mass engineering such as nuclear energy and geothermal development.the damage of high temperature rock mass has a great impact on the safety and quality of energy exploitation,and has attracted much attention in various high temperature rock mass engineering.In order to study the mechanical properties and failure mechanism of rocks under high temperature environment,this paper investigates the coupled thermomechanical(TM)behaviors,in real time,of granite containing three pre-existing fissures under uniaxial compression.The ligament angle spans from 75° to 120° with an interval of 15°,and the testing temperature varies from 25 °C to 700 °C.(1)The strength and deformation of the granite are first considered as functions of the temperature and the ligament angle ?.According to the experimental data,the elastic modulus of the granite greatly decreases at 400 °C,and the peak strength of the granite substantially decreases at 600 °C.In addition,the experimental results show that the fracturing behaviors of the granite specimens depend on not only the temperature but also the fissure array.For relatively small ligament angles,the crack coalescence between the inner tips of the pre-existing fissures only depends on the ligament angle,while for relatively large ligament angles,the crack coalescence between the inner tips of pre-existing fissures depends on both the ligament angle and the temperature.(2)The granite specimens mainly exhibit tensile failure modes at 25~200 °C,the brittle-ductile transition occurs at 300 °C,the granite specimens experience a mixed tensile-shear failure mode at 300~400 °C,and they experience a shear failure mode at T=500~700 °C.(3)In addition,the thermal damage of the granite is analyzed by thin section observation and electron microscopy scanning(SEM).Thin section observations show that the thermoinduced cracks in the granite mainly include intercrystalline cracks and intracrystalline cracks.SEM results show that the intracrystalline cracks and intercrystalline cracks occur dramatically in granite at T=400~700 ?.Electron probe micro analyzer(EPMA)experimental results show that the physical properties of the granite are considerably affected by temperature,while the chemical compositions of the minerals remain unchanged at T=25~700 °C.The damage to the microstructure ofthe granite at high temperatures is caused by physical changes rather than chemical changes.