Research On Different Scale Discrete Fracture Network Model And Permeability Of Rock Mass

Fractured rock is a combination of rocks and fractures, the fractures which are ubiquitously distributed in fractured rock mass often constitute the flow and migration path of underground fluid and radionuclide,thus have significant impacts on the seepage properties and stability of rock mass. It was found out that the Discrete Fracture Network Model (DFN) was a very effective tool to evaluate the mechanical tensor such as the hydraulic conductivity tensor of rock masses.Distribution of structural plane and major fracture sets were got based on in-situ observations and experiment,and three different scale models,which involve single fracture permeability coefficient that derived through theoretical study,were built to determine the hydraulic conductivity tensor of fractured rock masses reasonably.Based on the statistical characteristics of geometric elements of the fracture, the stochastic discrete fracture network model was built to characterize the structure of the rock mass using the Monte-Carlo method.As rock mass hydraulic conductivity is highly influenced by aperture,roughness and stress,the definition of those relations apt to describe the variability of the parameters was involed in the model.In addition, the theoretical single fracture permeability coefficient was revised by experiment.Then,with the use of Dijkstra algorithm,the seepage REV size of the small scale DFN and the hydraulic conductivity tensor could be obtained.In the submesoscale DFN,the "hole-effect" characteristic and the closure of the fractures were taken into consideration.This could not only reduce the fracture data of the DFN,but also make the model much more reliable.In the mesoscale DFN,as the persistence of joints might not be so good,the extra-child plates of fractures were inserted into the model,and the plate radius increased Manually.Then a shortest potential flow path was founded in the model.At the discontinuous district,smaller scale models were inserted,and then, the hydraulic conductivity tensor could be obtained.