STUDY ON CONNECTIVITY AND ENTROPY SCALE OF THREE-DIMENSIONAL FRACTURE NETWORK

The fracture network is complex in engineering rock mass, both the geometric characteristics and connectivity have an important influence on its permeability. In order to comprehensively quantify the influence of fracture trace length, dip angle, spacing and aperture on the connectivity and permeability of fracture network, basing on the principle of information entropy, the geological entropy theory and connectivity index entropy scale of three-dimensional fracture network is proposed. Compared the entropy scale with other traditional connectivity indexes, the rationality of entropy scale in evaluating the connectivity and permeability of three-dimensional fracture network is verified. The results show that the trace length of the fracture is negatively correlated with the entropy scale and the permeability coefficient. The fracture spacing and aperture are positively correlated with the entropy scale and the permeability coefficient. The dip angle of the fracture has little effect on the entropy scale and the permeability coefficient. The nonlinear relationship between entropy scale and permeability coefficient approximately satisfies quadratic polynomial. Basing on the statistical distribution of the fractures on the Left Bank Slope Jinping Hydropower Station, a numerical calculation method of three-dimensional fracture network seepage is established. By analyzing the relationship between the three-dimensional fracture network geometric characteristics and fracture areal intensity, dimensionless percolation density, entropy scale and permeability coefficient, The following conclusions are obtained: when the volume ratio is constant and the influence of aperture is considered, the fracture areal intensity and dimensionless percolation density cannot quantitatively characterize the influence of fracture network geometric characteristics. The length of fracture is negatively correlated with entropy scale and permeability coefficient. The fracture spacing and aperture are positively correlated with entropy scale and permeability coefficient. The dip angle of fracture have little influence on entropy scale and permeability coefficient. The nonlinear relationship between entropy scale and permeability coefficient approximately satisfies the quadratic polynomial.