| With the rapid development of nuclear energy in China,the proper disposal of high-level radioactive waste(HLW)has gradually become one of the key issues for nuclear safety and environmental protection.At present,the storage of HLW buried in underground repositories is internationally regarded as a safe and effective method,and the underground research laboratories(URLs)also play an important role in the development of verifying HLW deep geological disposal technology and evaluating site suitability.In this paper,the permeability of fractured granite rock in the area of URLs in northwestern China is taken as the goal of this research,and the three-dimensional seepage analysis program TPMFLOW is compiled.Due to the outcrop data of the fractured granite rock measured in the field,and through the statistical analysis of the parameters data,the program TPMFLOW was applicated to model,optimize and modify this 3D discrete fracture network at first.Then the program's equivalent pipe network model module and the trench pipe network model(TPM)module were applied to generate two kinds of pipe network models,which could be used to explore the representative element volume(RE?)size and the permeability tensor of the homogeneous areas I??.At last,the finite element model were generated to preliminarily predicts the seepage results in this large sites.The research work and corresponding results are summarized as follows:(1)Based on the 3D point cloud model constructed by digital close-range photography,abundant and accurate information of granite fractures were extracted.The program TPMFLOW was applicated to stochastically model the 3D discrete fracture network of disc-shaped.In order to eliminate the calculating error of the fracture diameter and volume density caused by the theoretical formula,diameter correction,volume density correction and depth correction were executed,which makes the model more consistent with field drilling data.Finally,the optimization of the model was performed to improve the calculation efficiency.(2)Applying modified fracture model to generate equivalent pipe network model,the three-dimensional discrete fracture network was firstly equivalent to a circular variable-section pipe element,then calculated and visualized with the result of nodal head distribution and velocity distribution in the form of pipe element.Finally,the RE? sizes and permeability tensors of the homogeneous areas ? to ? were extracted and visualized by TPMFLOW,which were basically in line with expectations:the ratio of RE? size to typical trace length approximately ranges between 7 and 11.The homogeneous areas ?,?,?,? and ? near the fault F31 to F34 are proved to have higher permeability,while the permeability tensor of the remaining homogeneous areas are relatively lower,basically remain at around10-10 m/s to 10-11 m/s.(3)In order to reduce a more appropriate imaginary trench characteristic of fluid flow between fractures,a trench pipe network model—TPM is proposed in this paper.The principle of the flow distribution and the flow redistribution in pipe element are used to form the theoretical part of the TPM analysis module,in which the distribution and the redistribution of flow are equivalent to the change of conductance.The result of permeability tensors in the homogeneous areas ? to ? were also predicted and then visualized,it shows that the values of TPM situation were slightly larger than the equivalent pipe network model,but the spatial distribution of permeability of the two models are almost the same.Moreover,the irregular body of the spatial permeability calculated by TPM is relatively more smooth,which means a more featable law of spatial permeability.The simulation results of permeability coefficient in homogeneous areas ?-1,?-2 and ?-3 are basically in the same order of magnitude compared with field drilling data.(4)The finite element model was established using above-mentioned data,such as equivalent permeability tensors parameters of each homogeneous area.And then preliminary analysis and prediction of the seepage characteristics of the large sites were obtained as well.It is concluded that the permeability is higher in the homogeneous area that is closed to the fault under the first boundary condition.This result of velocity is happened to be closely related to the permeability tensors of the medium.Except for the homogeneous area ?,the overall seepage of the research area in the model is mainly in the direction of fault F31,F34to F33 under the first boundary condition.And the magnitude of equivalent permeability coefficient of the model in this seepage direction is also low,which means the permeability law basically meets expectations.In general,the permeability in this area is relatively low,which means a suitable area for repositories of HLW and underground research laboratories. |
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