Calculation scale reduction on determining permeability tensor for fracture networks using tube element

Abstract:

To explore the preferential flow pathways of seepage in the fracture space, reduce the amount of calculation and make the model more practical under the premise of meeting the accuracy, according to the measured structural surface data, a three-dimensional (3D) fracture network with the same statistical characteristics as the field rock mass was generated by using the disc model, and the seepage channel was simplified to one-dimensional tube element model. The influences of reducing the calculation scale by group arrangement and full arrangement on the permeability tensor and the size of representative elementary volume (REV) were investigated respectively. The scale reduction effect was verified using practical engineering data. Results show that the reduction error of full arrangement was relatively small. When the calculation scale was reduced to 70%, the accuracy of the permeability tensor was basically unchanged. The REV size of the permeability tensor of the fractured rock mass increased with the increase of the reduction scale. There was indeed a backbone fracture network skeleton with larger diameter fractures controlling the seepage characteristics, and sufficient accuracy of the permeability tensor could still be ensured when the calculation scale of the fracture network was reduced to a certain extent.