Determination Of Seepage Tensor Of Three Dimensional Fracture Network By Rotating And Fitting

Rock mass is a very complex geological structure.Its macroscopical hydraulic properties depend on the structure of rock mass,mainly controlled by the distribution characteristics of structural planes and their combinations.The spatial distribution of structural planes,such as size,shape and occurrence,makes the seepage of rock mass heterogeneous and anisotropic,which determines the seepage analysis of rock mass is a complex and practical research topic.With the development of computer technology,computer simulation technology is used to determine the permeability characteristics of rock mass.Combined with field test,the seepage tensor reflecting anisotropy of rock mass is obtained at macro level.This method is widely applied.In this paper,a discrete fracture network model is applied to simplify the complex cracks into a pipe element model.Two methods are adopted to simulate the seepage tensor of fractured rock mass.One is using the constant head boundary method,calculation of multiple parameter sets of the seepage tensor,which is close to the actual situation of rock mass flow is more than one parameter model used in the past,to improve the accuracy of seepage analysis;the other is through a 3D rotation research domain,the optimal parameters by inversion method,through all directions the seepage coefficient and seepage ellipsoid fitting determination of seepage tensor.In the aspect of surface ele-ment model,some basic research work has been done in this paper,which lays the foundation for the calculation of surface element model in the future.The specific work is as follows:In actual situations,there are differences in the sizes of cracks in each rock mass.If a parameter is used as the ratio of all gap width to pipe diameter,the calculation error will be larger.In this paper,during the simplification of tube unit,according to the number of crack groups,multiple parameters are set as the ratio of gap width to diameter of each fracture.The optimal value of these parameters is determined by ge-netic algorithm,and then the seepage tensor of rock mass under the condition of fixed head boundary is obtained.At the same time,the advantages and disadvantages of the two methods in the calculation of seepage are also analyzed in the case of the gap width as the fixed value.Based on pipe element model,using the seepage ellipsoid to determine seepage tensor is a very effective method,but in the previous studies,to determine the ratio of gap width and diameter is obtained by using boundary head method inversion,the paper uses genetic algorithm in the ellipsoidal ratio on the gap width and the diameter of the quasi the process of inversion,determine the optimal gap width and the diame-ter of the value,which makes the final calculated seepage tensor is more consistent with the actual situation.In terms of the establishment of the surface element,the division method of tri-angular element on the single fracture surface is initially determined,which provides an effective method for future complex fracture structure meshing.In terms of seep-age calculation,a triangular element finite element method is simply provided.By this method,the node head and flow rate can be determined,which will make preparations for the seepage computation in the three-dimensional fracture network later.