Hydraulic and solute transport coupling model for fractured rock mass with discrete fracture network using computational method

The hydraulic and solute transport in fractured rock mass is of great importance for controlling the pollutant migration in groundwater. Based on the discrete fracture network model, a 3D computational method is proposed to investigate the coupling behavior of hydraulic and solute transport in fractured rock mass, with rock matrix modeled by solid elements and complex fracture networks represented by the zero-thickness elements. The proposed method is validated against the results from the refined modeling and analytical approach in the case of solute transport in a fracture-matrix system without and with reactions. It is further employed to simulate the mass transport process in fractured rock mass containing a large-scale fracture network, to predict the solute concentration distribution and to estimate the main influencing factors of the solute field. It is shown that the proposed numerical method is capable of capturing the water and solute movement in the fracture network and rock matrix. Due to the dominant flows in the percolated fracture network, the solute plume is greatly affected by convection of water flows in fractures, resulting in a highly heterogeneous distribution. With the aid of parametric sensitivity analysis, it is demonstrated that the convection effect attributable to fracture aperture is the main control factor affecting the solute field, compared with the diffusion effect caused by fracture matrix. On the premise of ensuring the calculation accuracy, the proposed method brings down the computational cost and also possesses an apparent advantage in settling down the three-dimensional computational solution for fractured rock mass containing a complex discrete fracture network.