An Investigation Of Thermal Effects On Mesoscopic Properties Of Granite By X-ray CT Technique

In many high temperature rock engineering,such as the development of geothermal energy,deep disposal of nuclear waste,the underground gasification of coal,and the multiple exploitation of oil,the seepage and mechanical properties of the rock under the effect of high temperature are changed.The reason is generation,propagation and gathering of micro-cracks induced by high temperature.Moreover,the spatial location and spatial distribution of micro-cracks will significantly affect their mechanical properties under external loading conditions.Therefore,it is helpful to reveal the mechanism of the change in material macro-properties that studying thermal effect of rock from micro view and the heterogeneity and anisotropy of the spatial location and spatial distribution of micro-cracks,which is important for the safety of the high temperature rock mass engineering.In this paper,the variation of porosity,heterogeneity and anisotropy of granite after thermal treatment at different temperatures,after circulating thermal treatment at 500 °C and after rapid cooling in water are studied based on X-ray Computed Tomography technique.The high temperature can significantly influence the micro-properties of granite.The porosity of granite increases obviously as temperature increases between 400 °C to 800 °C.It is slightly influenced by temperature beyond this range.The heterogeneity and anisotropy of granite are mainly dominated by the initial cracks below 200 °C.However,the temperature is higher than 200 °C,the heterogeneity and anisotropy are mainly determined by cracks induced by the temperature.At 500 °C,both of the heterogeneity and anisotropy of granite increase to their maximums.When the temperature is high enough,such as 1000 °C,the granite is almost isotropic material.The first thermal loading at 500 °C has a significant influence on the micro-properties of granite.Subsequently the multiple cyclic thermal loading has no obvious influence on micro-properties of granite.After the first thermal loading,the porosity,heterogeneity and anisotropy of granite all increase significantly.Subsequently in the process of multiple cyclic thermal loading,the porosity,heterogeneity and anisotropy change slightly.Rapid cooling method could significantly affect the micro-properties of granite.At 800 °C,the internal damage of granite after water cooling is obviously greater than that after natural cooling.And the granite material cooled by water is more homogeneous and isotropic than that cooled naturally.