Experimental Research on Creep Properties of Hard Rock under Long-term Load Conditions

— As the excavation depth of underground engineering increases, the engineering becomes more and more complex. The splitting failure of underground caverns of large hydropower station is a common phenomenon that was not accounted for theoretically so far, which is one of the important factors affecting the safety of underground construction and the long time running stability. Long-term load conditions and great depth are considered to be the main factors that lead to the creep deformation of underground hard rock mass. Therefore creep tests under long-term load conditions are conducted for the purpose of studying the creep properties of the deep hard rock mass. An important hydropower station is taken as the research background project, and the Granite is taken as the research object to carry out the long-term creep test. During the test, the effect of long-term load conditions of hard rock is mainly recorded. Based on the results of the systematic analysis, it is concluded that the mechanical properties of granite are largely affected by high stress: (1) The creep process of granite can be divided into three stages: the transient creep, the steady creep, and the accelerated creep, with different strain rate in each creep region. (2) The granite generates instantaneous deformation at every loading level, the higher the confining pressure, the greater the initial transient strain. (3) The creep deformations of specimens increase with time and stress, it begins to appear an obvious creep deformation when the stress level reaches a certain value, the higher the confining pressure, the greater the creep deformation, and the earlier the creep phenomenon. (4) The higher the confining pressure, the shorter the creep duration, and the more liable to be broken. (5) With the increase of confining pressure, the rock tends to shear failure.