Study On Coupling Mechanism Of Rock And Pore Water Under Cyclic Loading

The research on the characteristics of rock deformation failure and the damage evolution under cyclic loading is one of the frontier topics of rock mechanics and engineering. It also contributes to the correct understanding of the rock failure mechanism under cyclic loading, thus the long-term stability of engineering rock mass is scientificly evaluated. The fine sandstone, mudstone and limestone that are common in the Three Gorges reservoir area are taken as the study objects, among which the fine sandstone is the major object. The MTS815 Rock Mechanics Test System, RLW-2000M Coal and Rock Computer Controlled Rheological Testing Machine from State Key Laboratory of Coal Mine Disaster Dynamics and Control (Chongqing University) are applied to carry out these experiments, and the theories, such as seepage mechanics, damage mechanics, rock hydraulics and so on, are applied to do a helpful research. The results are gained as follows:1) In the experiment of monotonic loading strength failure, different stress-strain curves, from the test of uniaxial compression under different moisture content, the test of triaxial compression under different pore pressurem, and the test of triaxial compression under different confining pressure, are analyzed. The failure effects on rock strength by moisture content, confining pressure and pore pressure are studied.2) When different pore pressures keep constant, the creep process of axial and transverse strain can be divided into four stages. At the beginning stage, the rate of water flow reduces relatively quickly; at the steady stage, it becomes stable, and increases gradually at the accelerating stage; finally at the stage of creep destruction, it increases suddently at a high speed.3) The uniaxial cyclic axial stress experiments were carried out in different circumstances, including different water state (saturated, dry, drying), different stress levels, and different loading rate; meanwhile, the triaxial cyclic axial stress were performed in different confining pressure. Based on experimental results, the evolution laws of the cyclic axial stress -strain hysteresis curve are respectively analyzed, and the cyclic hardening and softening of rock are further studied.4) In the experiments of cyclic confining pressure under constant and variable amplitude conditions, the evolution law of rock deformation, cyclic hardening and softening, destruction features and fatigue damage characteristics are analyzed. Affected by pore water pressure, evolution law of water flow, together with the evolution law of rock deformation, cyclic hardening and softening, destruction features and fatigue damage characteristics, are analyzed in the experiments of cyclic confining pressure under constant and variable amplitude conditions.5) Cyclic hardening and softening behaviors, hysteretic characteristics, failure characteristics, fatigue damage characteristics, and the evolution law of rock deformation are researched in cyclic pore pressure tests, under different axial stress, different confining pressure, different range of pore pressure, different pore pressure amplitude, different cyclic pore pressure rates, different cyclic pore pressure constant time, and different rock materials.6) Through rock and pore-water coupling mechanism, four deformation stages can be distinguished, which are stage of water filling in pores and compression of pores, stage of elastic coupling effect, stage of yielding coupling effect and stage of fatigue failure. Through rock articles and pore-water coupling mechanism, four states appear, which are state of initial stress and water saturation, state of loading pore pressure, state of unloading pore pressure, and state of pre-fatigue failure.7) A statistical damage constitutive model of rock in axial compression, which is more simple and more universal, is put forward by using equivalent strain hypothesis, rock damage mechanics and weibull distribution of micro-unit strength. The secant poisson ratio is taken as variable of the model.8) The curve of fine sandstone deformation evolution law, cyclic hardening and softening, and strain hysteresis are analyzed in the experiments of fine sandstone fatigue damage deformation under cyclic pore-water pressure. Simultaneously,the fatigue damage variable evolution rule and cycle fatigue damage evolution equation are investigated, therefore fatigue damage model of rock under cyclic pore pressure is established based on the above parameters.