Experimental study on creep properties of gneissic granite at high temperatures

The increase of excavation depth of underground cavern leads to the instability of surrounding rock. Geothermal energy and great depth are considered to be the leading factors that result in the creep deformation of underground hard rock mass. So creep tests at high temperature and high stress are performed by using the rock automatic three-axis servo rheometer for the purpose of researching the creep behavior of the deep underground hard rock mass. Firstly, the samples in site were taken back to the laboratory, and then were processed into cylindrical specimens in accordance with the specification. Secondly, the test scheme was designed with three temperature and three confining pressure conditions on the basis of the real geology of the hydropower station engineering, and after that, the long experimental process began. Finally, the test data were dealed with computer to obtain the various curvilinear relationship, and the test features were also described in line with the testing phenomenon. The conclusion throughout the results of the systematical analysis indicates that the that the mechanical properties of granite are largely affected from elevated temperatures and high stress. That is, when at the same temperature conditions, the creep deformation increases with the increase of stress, while when at the same surrounding pressure conditions, the creep deformation increases with the increase of temperature. However, the changing trend of the long-term strength is diverse. In other words, the long-term strength of rock increases with the increase of the surrounding pressure at the same temperature conditions, but decreases with the increase of the temperature at the same temperature conditions.