三尺度、多组分、多场耦合溶质运移机理及模型研究

Multicomponent solutes transport under multifield and multiscale conditions is of widespread relevance with many diverse projects in geoenvironmental engineering, such as the construction and maintenance of municipal solid waste landfill, the cut-off of groundwater and contaminated soils. This project is based on mechanism analysis, establishment of theoretical model, Lab tests and numerical simulation. Applying the hybrid mixture theory, a three-dimensional hydraulic-mechanical-chemical fully coupled model for multicomponent system will be developed. The model is multiscale as it includes three levels of observation: micro, meso and macro. The distinction between the micro-, meso- and macrostructure provides the opportunity to describe and explain the interaction mechanisms between soil particle, solute and pore water, to take into account the dominant phenomena that affect the behavior of each structural level and the main interactions between them comprehensively and accurately.A series of permeability tests will be carried out in flexible-wall permeameters and test chamber to specify the model parameters. The processes of solute transport and transformation in clay liner under complex infiltration conditions will be simulated and reproduced with the proposed model using COMSOL Multiphysics. The simulation results will be analyzed to predict and evaluate the long-term performance of the barriers, based on which one can propose measures of seepage and contaminant transport prevention. The results of this research are potentially significant to provide theoretical foundations and scientific basis in designing the waste contaminant barriers and evaluating its environmental safety for large-scale landfills in our country.

在城市固废堆场建造运维、污染场地地下水围封阻隔等环境岩土工程领域中，均会涉及到三尺度、多组分、多场耦合条件下的溶质运移问题。本项目拟通过机理分析、理论建模、室内试验和数值模拟相结合的方法开展研究。基于复合混合物理论，建立多组分、跨尺度耦合的水力—力学—化学多场全耦合模型，主要针对影响溶质运移的土颗粒、溶质、孔隙水三者间相互作用机理、影响不同尺度结构行为的主要机制以及不同尺度间的相互作用给予全面、准确的描述和解释。采用污染土柔性壁渗透仪和自制试验箱体开展系列室内试验，借助多场耦合分析软件COMSOL Multiphysics对所建模型进行数值求解，从而揭示复杂入渗条件下溶质在防渗黏土垫层中的运移转化规律，并对水力防渗屏障的长期服役性能进行预测和评价，进而提出相应的防渗隔污控制措施。该项目研究能够为我国大型垃圾填埋场防渗系统的设计及环境安全性评价提供重要的理论基础和科学依据。

针对复杂条件下的溶质运移机理开展了深入系统的研究，研究成果能够为设计合理、经济的防渗系统提供理论依据，对于堆场防渗系统的设计及隔污垫层长期有效评估具有重要的实际意义。主要研究工作和成果如下：.（1）在微观尺度和宏观尺度框架内，基于有效浓度描述的离子微观质量平衡方程和动量平衡方程，采用体积平均技术，推导了离子的宏观质量和动量平衡方程。.（2）在离子的运移方程中引入了活度系数，构建了适用于多孔介质材料的可考虑孔隙液相组分活度的多组分溶质非线性扩散理论框架。.（3）基于推导离子宏观动量平衡方程，通过给定相关驱动力的具体本构方程，建立了多离子体系在黏土垫层中的扩散方程。.（4）考虑溶质扩散的依托环境，对受土体电场影响的溶质离子活度系数模型进行修正，建立了基于动量平衡的多组分溶质在带电性黏土中的扩散模型。.（5）引入Guntelberg修正活度，基于化学势表征扩散驱动力的广义线性扩散通量方程，考虑扩散势和黏土半透膜效应对离子扩散行为的影响机制，建立了非理想体系下多离子在黏土垫层中的扩散模型。.（6）基于微观平衡方程，通过体积平均化方法得到多离子在宏观尺度上采用质量分数描述的质量平衡方程，能够描述组分在黏土中质量交换的现象。.（7）基于不可逆热力学原理构建了组分质量交换与系统能量耗散以及化学势之间的关系，建立了非平衡吸附模型的理论框架。 .（8）考虑多组分溶质共存的实际情况，在自由能函数中引入活度系数，建立了多组分溶质在黏土中的非平衡吸附模型。.（9）建立适用于填埋场黏土垫层的水-力-化全耦合溶质运移模型，考虑了溶质运移过程中土体物理特性、水力特性及输运特性的变化及对土体宏观特征和溶质运移的影响，实现了应力场、渗流场和浓度场的完全耦合，能够综合描述黏土垫层变形、孔隙液流动及溶质运移规律。