Study On The Damage Evolution Mechanism Of Fractured Rock Mass Under High Seapage Pressure

Water pressure within the joints and fractures of rock masses results in diversification of the stress across the fractures and the decrease of mechanical strength. The rupture of the fractured rock masses and water inrush is induced by the expending, perforation and damage of fractures within rocks under engineering disturbance-seepage pressure coupling effect. The damage evolution mechanism of fractured rock masses under high seepage pressure were investigated systematically by the combined methods of in-situ test, laboratory test, numerical simulation and theoretical analysis. The main conclusions are as follows:Five phases in the complete stress-strain process of the rock mass were proposed, which show different characteristics of acoustic emission frequency and the rate of energy, as well as the variation of permeability. The damage of rock masses under seepage pressure is influenced by the confining pressure, which inhibits the damage, and influenced by seepage pressure within the fractures which stimulates the damage. The permeability of rocks was related by its damage and shows the external manifestations of damage. The permeability evolution corresponding to the damage of rocks shows obvious stages. A mutation increase point exits in the permeability evolution process.Based on the results of in-situ high seepage pressure water test of fractured rock masses, the relevance between the permeability of fractured rock masses and seepage pressure is analyzed. With the increase of seepage pressure, the permeability of fractures rock increases as an exponential function, and the increase trend occurred the obvious sectional feature which is expressed that there are obvious mutation points in the increase curves of hydraulic conductivty. Analysis shows that the main reason leading to the increase of hydraulic conductivty is the increase of the opening of the fracture surface under the hydrostatic pressure affect. Through the fitting analysis of test data, the connection appraisal model of the hydraulic conductivity of fractureed rock mass with the initial seepage capacity and fracture state parameters(openness and stiffness) under high seepage pressure is derived.By using the theory of fracture mechanics, considering the crack closing and opening, I make a theoretical analysis on the crack initiation and propagation mechanism of the fractured rock masses under the hydraulic pressure. The analysis shows that the size of the seepage water pressure is inversely proportional to the crack initiation strength, the size of confining pressure is proportional to the crack initiation strength, the radius of curvature of the crack tip is inversely proportional to the crack initiation strength. In the study of the propagation of the crack under the osmotic pressure, it is found that whether the crack is open or not, the seepage water pressure increases the crack propagation and the confining pressure is the opposite.Under the action of artificial disturbance and ground water seepage, the deformation process which is often associated with the flood disaster of the fractured rock mass from stable state to unstable failure can be divided into two stages: stable evolution and abrupt instability. From the perspective of the damage evolution mechanism of fractured rock mass, the permeability of rock fracture is mainly controlled by the opening degree and the connectivity of the fracture, and influences the strength of seepage pressure and the stress state of rock mass. After the failure and instability of the rock mass, the seepage pressure will increase rapidly, which leads to the great change of the seepage state of the fractured rock mass.With numerical study of the damage and failure of the floor of mining coal seam above the confined water carried out, the evolution law of stress field, damage, fracture and seepage field were researched. The influences of roof caving, floor heterogeneity and water pressure on the damage and fracture of the floor and the evolution of seepage were analyzed.