Study on the Effect of Sandstone Microscopic Damage and Dynamic Compressive Properties After Heat Treatment

It has important guiding significance to study the influence of high temperature on physical and chemical properties and dynamic compression mechanical properties of rocks on the stability of rock mass engineering involving thermal behavior. The damage characteristics and dynamic mechanical characteristics of sandstone after different temperatures (20 °C, 200 °C, 400 °C, 600 °C, 800 °C, 1000 °C) are studied. The mineral composition, mineral content and pore structure of sandstone changed significantly after heat treatment. The content of clay minerals decreases and the content of quartz increases. And all the internal hematite is reduced at 400 °C. The content of macropores increases, and the pore size range decreases. The Split Hopkinson pressure bar is used to perform uniaxial impact compression tests on the heat-treated sandstone specimens with different average impact speeds (8.6 m/s, 14.6 m/s and 18.8 m/s). It is found that the impact speed would weaken the degrading effect of temperature on sandstone, and the temperature would increase the strengthening effect of strain rate. The change of the dynamic elastic modulus of sandstone under the coupling effect of temperature and loading includes the temperature weakening stage, the impact load enhancing stage and the temperature weakening stage. A damage dynamic constitutive model considering the combined effects of temperature initial damage and impact loading damage is established according to the study of the macroscopic and mesoscopic degradation characteristics of sandstone by temperature. The rationality of the model is verified.