Damage Deformation And Energy Characteristics Of Granite Subjected To Cyclic Loading

Rock is known as a kind of medium material in the construction of tunnel engineering, foundation engineering and mining engineering; therefore, its mechanical properties are the foundation of construction safety. Engineering practice shows that rock mass will be subjected to cyclic loading during the stages of construction and operation of underground engineering, such as geological formation movement, seismic action or excavation and supporting of underground caverns. Then the mechanical properties of rock under cyclic loading play an important role in the long term stability of the geotechnical engineering construction. Rock mass is a kind of complicated geomaterial and its mechanical response is non-linear and anisotropic. According to the damage deformation and energy characteristic s of rock element under different confining pressures, a series of tests on rock subjected to cyclic loading and unloading are carried out.Based on the current rationale of damage, the damage variable is revised. Then a new calculation method of damage variable is proposed in the process of cyclic loading and unloading. On this basis, the relationship among damage variable, plastic strain, axial stress and cycle index under different stress levels is explored. Meanwhile, the evolution laws of deformation modulus and volumetric strain with the changing cycle index and axial strain are analyzed.The energy of rock is mainly composed of elastic energy and dissipated energy. The microscopic calculation method of dissipated energy is proposed based on the relativity principle and the difference between total energy and elastic energy. Subsequently, according to the stress-strain curve of rock under cyclic loading, the revolution laws of dissipated energy with a variable of cycle index, axial stress, deformation modulus, plastic strain and damage variable are obtained.Based on the damage deformation and energy transformation rule of granite in the process of fatigue damage, the threshold value of fatigue damage is analyzed quantitatively from the view of dissipated energy and damage variable. The threshold value is consistent with the one using volumetric strain as the control parameter. The fatigue damage states are different under different confining pressures, however, there is a significant linear correlation between the dissipated energy and damage variable before destruction. An equation for energy is proposed based on the analysis of dissipated energy and damage variable.