裂隙岩体渗流溶质运移耦合离散裂隙模型数值计算方法

研究裂隙岩体渗流溶质运移问题对于岩土工程地下水污染物预测控制具有重要意义。基于离散裂隙网络模型,采用实体单元模拟基质岩块、无厚度单元模拟复杂裂隙网络,提出了裂隙岩体渗流溶质运移耦合的三维数值计算方法。针对无反应项和含反应项两种情况,通过算例分析了单裂隙中溶质迁移行为,并与精细模拟方法、解析方法的结果进行对比验证;进一步将该法应用于预测大规模裂隙岩体溶质浓度分布规律及发展趋势,并评价了主要影响因素。结果表明,该法可有效模拟裂隙网络、基质岩块中水分溶质传输行为;由于贯通裂隙网络的优势流影响,溶质羽主要受控于裂隙水的对流作用,出现了高度非均匀分布现象;通过参数敏感性分析发现,相较于岩块基质的扩散作用,裂隙开度产生的对流作用是影响浓度场分布的主控因素。在保证精度的前提下,该法可大幅减小计算量和计算时长,对于解决含复杂裂隙网络岩体渗流传质的三维数值模拟问题具有明显优势。

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.