TRIAXIAL UNLOADING TEST OF SANDSTONE AFTER HIGH TEMPERATURE
LI Jianlin1,CHEN Xing2,DANG Li1,DONG Yanhua3,CHENG Zhuang1,GUO Jing1
(1. Key Laboratory of Geological Hazards in Three Gorges Reservoir Area,Ministry of Education,China Three Gorges University Yichang,Hubei 443002,China;2. Multipurpose Project Administration,China Three Gorges Corporation,Yichang,Hubei 443002,China;3. College of Hydraulic and Environmental Engineering,China Three Gorges University,Yichang,Hubei 443002,China)
Abstract:Comprehensively considering the relationship of the rebound value and longitudinal wave velocity with the temperature,the change laws of the longitudinal wave velocity and mechanical characteristic with temperature of the sandstone after high temperature are studied by triaxial unloading test. The test results show that:(1) The longitudinal wave velocity of the sandstone becomes lower with the increase of baking temperature. And the velocity decreases more rapidly while the temperature becomes higher. (2) With the increase of baking temperature,the rebound value of the sandstone is not a simple monotone increase/decrease. (3) The mechanical properties of sandstone change under the interaction of friction characteristics and cement properties. The friction characteristics strengthen greatly after high temperature baking;and then,the strength of sandstone increases greatly under the high confining pressure. (4) The longitudinal wave velocity,rebound value and strength don?t have inexorable law after high temperature baking. (5) The unloading damage of natural air-dried rock samples under low confining pressure still shows a significant compression and shear failure mode. (6) By analysis of the test results,we believe that the tensile strength of rock samples decreases significantly after high temperature baking. The interior of sandstone produces the thermal stress after heat treatment. The thermal stress induces the thermal cracking of the surface and internal microcracks,which is the essential reason of the tensile strength decreasing.
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