Study On Size Effect Of Permeability For Fractured Rock Mass As Well As Its Influencing Factors

In the larger rock engineering design, construction, operation and maintenance process, the property of fractured rock mass permeability and its changes determined the characteristics of rock mass seepage and the control effect of hydraulic structures on seepage flows. Finally, it also has major effects on the stability and safety of the engineering structure, and is a main issue which needs deeply research. Therefore, some related research and evaluation methods about the topic of rock mass permeability characteristics and its influencing-factors, more and more are taken seriously.As the existence of structural planes in rock mass, such as joints, cracks, weathered bedding, dykes interfaces, geological faults and so on, the inhomogeneity, discontinuity, anisotropy and other rock mass features become more significant. Therefore, mechanics and seepage characteristics of fractured rock mass are different from those of general homogeneous medium. Rock mass is composed of complex geological body. It is made up of rock matrix and various geological structural plane. The latter is formed by the action of geological tectonix activities. Because of the complexity and variability of rock mass structures, the characteristics of inhomogeneity, anisotropy and nonlinearity all intensively present. But in geotechnical engineering, on the one hand, excavations of rock mass in engineering, are likely to result in the initial stress field within rock mass to change to some extent, such as crack initiation, sliding, opening, closing, extension and so on. Then, the structure of rock mass were changed, and caused the change of seepage characteristics of rock mass. On the other hand, the completed geotechnical engineering structure, changes the groundwater seepage field of some corresponding area, finally resulting in the change of the stability of the rock mass within the domain. Therefore, the study on seepage characteristics of fractured rock mass is of important significance in the practice of geotechnical engineering.In this paper, the study is focused on the size effect of permeability for fractured rock mass and its influence factors. Specifically, this includes:the significance to research on permeability characteristics of fractured rock mass; how to determinate the permeability coefficient of fractured rock mass; the size effect of permeability coefficient for fractured rock mass and its influence factors. The contents are as follows:(1) The basic theory of fractured rock mass seepage was investigated. The influence of crack to rock mass permeability properties, including spatial structure and geometric parameters are analyzed.(2) In order to simulate the fracture network of rock mass, Monte-Carlo method was mastered. Then the fracture network models were generated. Fracture geometry distribution model and the fracture network generation technique based on Monte Carlo method are introduced.(3) The Cubic Law is introduced, and is revised.(4) The fundamental principle of the discontinuous displacement method is given.(5)The permeability coefficients of fractured rock mass from numerous samples of randomly generated fracture networks are substantially calculated, and their size effect is studied in detail. Then the impact about its influence factors, such as groundwater pore pressure, the initial ground stress, young’s modulus and poison’s ratio, is analyzed.(6) Discussion and conclusion...