Research On The Influence Factors Of Fractured Rock Mass REV Size And Equivalent Permeability Coefficient

The seepage of fractured rock mass is very important to the safety of underground engineering.In the field application,the equivalent continuum method is one of the most commonly used methods to study the seepage in fractured rock mass.Due to the randomness of fracture distribution and the anisotropy of fracture,there is not necessarily representative unit volume(REV)in macroscopic view,and the fractured rock mass does not necessarily meet the permeability tensor characteristics.The applicability mechanism of the equivalent continuum method to study the seepage flow in fractured rock mass is not completely clear.In view of the fact that the density,trace length,direction and roughness of fractures are important factors affecting REV size and permeability characteristics of fractured rock mass,a seepage program of two-dimensional fracture network is developed in this paper,and the effects of fracture density,trace length and roughness on REV size and permeability characteristics of fractured rock mass are studied respectively.The main research results and conclusions are as follows:(1)According to the known distribution information of geometric parameters,a twodimensional discrete fracture network is generated based on Monte Carlo method.According to the breadth first algorithm,the main fracture network is drawn,and the influence of different statistical distribution on fracture connectivity and fracture connectivity is explored.The results show that the fracture connectivity and fracture connectivity of fracture network with uniform azimuth distribution are greater than those with normal distribution.The fracture connectivity of fracture network with lognormal trace length distribution is less than that of fracture network with negative exponential trace length distribution.There is a good nonlinear relationship between the fracture density and the number of connected paths,and a good linear relationship between the fracture length and the number of connected paths.(2)The mathematical model of two-dimensional fracture network discontinuous media seepage is improved,and the corresponding calculation program is compiled by MATLAB software.The correctness of the program is verified by the corresponding calculation example.The equivalent permeability coefficients of fracture networks with different statistical distributions are calculated.When the fracture length is smaller than that of the study area,the equivalent permeability coefficient of fracture network with uniform azimuth distribution is greater than that of fracture network with normal azimuth distribution.The equivalent permeability coefficient of fracture network with lognormal trace length distribution is greater than that of fracture network with negative exponential trace length distribution.(3)The REV size and permeability tensor of fractured rock mass are calculated by using the developed seepage program of fracture network.The REV size and permeability tensor of fractured rock mass with different fracture density,trace length and roughness are analyzed.The results show that with the increase of density and trace length,the REV size of fractured rock mass decreases gradually.When the fracture density and trace length reach a certain value,the fractured rock mass has good tensor properties.With the increase of relative roughness,REV size of fractured rock mass increases gradually.