三维裂隙网络中典型重金属污染物反应运移数值模拟

Reactive Transport Numerical Modeling of Typical Heavy Metal Pollutants in Three⁃Dimensional Fracture Networks

自然界中裂隙介质的具体结构往往控制着其中的水流流动和溶质运移过程.由于真实裂隙网络的复杂性,常据不同裂隙参数(形状、位置、大小、密度、走向等)概化并使用特定数学分布来刻画和产生离散裂隙网络,但这种离散裂隙网络介质因其高度非均质性和各向异性导致传统基于多孔介质理论的数值方法难于模拟裂隙水流和溶质运移过程.利用三维离散裂隙网络模型生成场地裂隙介质不连续体,并基于裂隙空间参数将离散裂隙网络模型映射为等效多孔介质模型,由此进一步耦合地下水流与多组分反应性溶质运移开源代码PFLOTRAN,以实现三维裂隙网络中重金属污染物反应运移过程的数值模拟与污染物通量的定量评估.算例研究表明,随着裂隙密度的增大,裂隙网络表征逐渐趋近于多孔介质;裂隙发育的密度和方向均影响着裂隙网络的连通性,进而影响裂隙水流中不同组分的迁移规律和通量评估,其中保守性组分与不同反应性组分的迁移行为有明显差异.同时,研究表明,裂隙粗糙度对刻画裂隙网络中的污染组分迁移过程和通量评估具有重要影响.本文方法可为场地裂隙介质中地下水流和污染物的反应运移提供有效模拟手段和定量评估工具.

The geologic discontinuities present in natural fractured rock governs groundwater flow and solute transport process.Due to the complexity of real-world fracture network,discrete fracture network(DFN)is often be described and generated based on specific probability distributions determined by different parameters(shape,location,size,density,orientation,etc.).Due to DFN’s highly heterogeneous and an isotropic features,it´s a challenge to simulate groundwater flow and solute transport processes using traditional numerical solution based on the experience achieved in porous media.In this paper,a 3-D DFN model is built for field-scale study,and mapped to an equivalent porous medium(EPM)model,which further couples groundwater flow model with the multi-component reactive transport code PFLOTRAN to achieve numerical simulation of the reactive transport process of heavy metal contaminants in the fractured network and quantitative assessment of mass fluxes.The study shows that the behavior of the fracture network gradually transforms into the transport in porous media as the density of the network increases;Both the density and orientation of fracture development affect the connectivity of the fracture network,which in turn affects the migration pattern and flux assessment of different components in fractured rock groundwater flow,where the migration behavior of conservative components and various reactive components are significantly different.Meanwhile,it is shown that roughness has an important influence on the migration process and flux assessment of the transport components in the fracture network.This paper provides an effective simulation and quantitative assessment tool for the reactive transport of heavy metals and groundwater flow in the fractured field.