Improved Three-demensional Discrete Fracture Network Model And Multi-scale Pipe Network Model With Its Application Research

Taking the permeability of fractured granite rock at a high discharge waste laboratory site in northwest China as the research target,a three-dimensional discrete fracture model generation program and a multiscale pipe network model were compiled based on Matlab.Through the measured rock outcrop data in the site,the program was compiled to model the 3D discrete fracture network model and generate the parameter corrections by combining the combined morphology of the joint surface parts with the parameter statistical analysis.The equivalent pipe network model is used to calculate the modeled seepage characteristics of each homogeneous zone and obtain the corresponding permeability tensor as well as the main value of permeability and main direction.The equivalent permeability coefficient in each direction is used as the object,and the permeability tensor ellipsoid is fitted with the main direction of the permeability tensor in the radial direction.And based on this ellipsoid and the equivalent pipe network model,a composite pipe network model for wide-scale seepage analysis considering the influence of different scales of structural surfaces is proposed,and the fluid seepage characteristics over a wide area in the region are predicted by this model.The research work and corresponding results are summarized as follows.(1)Based on the traditional discrete fracture model,considering the partial mechanical genesis of the site rock joint surface,the conjugate structural surface is added to the model and the program is written to generate an improved 3D fracture network model.Body density and radius calibration of the structural surface is carried out to eliminate the error between the parameters of radius and body density of the structural surface calculated by theoretical equations and the actual situation,introduce correction coefficients,and regenerate the model using the corrected structural surface parameters.(2)Extract the reconstructed model skeleton,generate the equivalent pipe network model,equate the3 D discrete fracture network into circular variable-section pipe units,calculate the nodal head distribution and visualize it.The scale of the rock characterization unit body in each homogeneous zone is calculated,the study domain is established with the corresponding scale and the model is generated,the equivalent permeability coefficients in multiple directions are obtained,and the corresponding permeability tensor results are calculated and visualized.The permeability coefficients of Ⅰ,Ⅲ-1,Ⅲ-2,Ⅲ-3,Ⅳ and VI homogeneous zones range from 4.542e-9 m/s to 1.815e-8 m/s;the permeability coefficients of Ⅲ-4,Ⅱ and V homogeneous zones range from 4.170e-8 m/s to 5.946e-8 m/s.Based on the main direction of the permeability tensor,the equivalent permeability coefficients in each direction are used to fit the permeability tensor ellipsoid.(3)A composite pipe network model for large-scale seepage analysis considering the influence of structural surfaces at different scales is proposed.The large-scale study domain is established,and the program is used to divide the tetrahedral grid and calculate the node and pipe information to form the rock matrix pipe network model.In the model,it is assumed that each pipe bears one-sixth of the regional seepage of each tetrahedral rock matrix unit adjacent to it.The hydraulic conductivity of the pipes is obtained by taking values on the ellipsoidal surface of the infiltration tensor in the corresponding homogeneous zone and back-calculating them with the volume of the area bearing the seepage.The equivalent permeability coefficient is calculated to verify the usability and correctness of the model.(4)Based on the rock matrix pipe network model,a composite pipe network model incorporating large structural surfaces and fracture zones is established respectively for preliminary analysis and prediction of the site area in the pre-selected area.The overall seepage direction of the model in the study site area is from west to east,and in this direction,the macrostructure surface promotes the steady-state seepage in the overall area,but the accelerated change of water head with the fracture zone makes it "block" the seepage in the local area,which theoretically supports the rationality of establishing an underground laboratory and a high discharge waste repository in the area.This theoretically supports the rationale for the establishment of an underground laboratory and a high-level waste repository in this area.