非饱和土壤胶体非均匀输移显色示踪技术与数值模拟研究

Investigations of colloid movement through unsaturated soils are driven by a variety of issues, including contaminant transport, and subsurface migration of heavy metals, phosphorus, pesticides and pathogenic microorganisms. The objectives of this project are to determine soil hydrology driving mechanism for heterogeneous colloid transport in unsaturated soils, to reveal the impacts of soil physcial and chemical properties on the colloid transport, and to develop a physcial-based model to simulate heterogensous colloid transport in unsaturated soils. We will develop and test a method to visualize macropores, heterogeneous soil water flow, and colloid paths in soil profiles. In-situ field experiments will be conducted under various boundary conditions and at different measurement scales to investigate the spatial and temporal characteristics of heterogeneous soil water flow and colloid transport processes in the unsaturated soils. We will solve the key scientific problems in the simulation of the heterogeneous colloid transport. These scientific problems include the impacts of unsteady soil water flow process and changes of soil physics and chemical properties on colloid transport, and the description of the fast migration of colloid with preferential soil water flow movement in a three-dimensional mesh region. Physical model will be developed with general constitutive functions to describe the interaction of soil physical and chemical properties and flow heterogeneity on the colloid transport. This fundamentally important project will provide the essential information for solving theoretical and practical issues of the groundwater environment and to provide a new model to describe complex colloid transport proceese in the unsaturated soils.

本项研究将发展全域性的三维示踪方法，实现对非饱和土壤性状、非均匀水流运动和胶体同步输移信息的完全测定；通过开展系统的实验，研究非饱和土壤中胶体非均匀输移特性在空间和时间过程中的变化规律，揭示非饱和土壤中非均匀流动对胶体输移的驱动机制，以及胶体在水动力、土壤物理及化学性状共同作用下的输移响应机理；解决非饱和土壤中胶体输移模拟所遇到的非均匀流动维数与计算网格维数不一致、非饱和土壤介质性状变化及高度非稳定水流驱动下的胶体非线性过程响应问题，发展具有普适性的非饱和土壤介质性状-非均匀水流驱动-胶体输移响应本构关系方程，构建具有完备物理机制的非饱和土壤胶体非均匀输移数值模型。为土壤水、地下水中与胶体相关的污染物迁移特性及其环境效应研究提供理论和方法支撑。

针对非饱和土壤中胶体非均匀迁移全局性示踪方法、胶体非均匀迁移行为特性、非饱和土壤介质性状变化-非均匀流动模式-胶体非均匀输移机理、和非饱和土壤非均匀胶体输移物理模型开展了系统性的实验研究、理论探索和模型构建工作。发展了基于Fe2+-TiO2电子转移的胶体全局性示踪显色成像示踪方法和基于各项异性的紫外偏振光（ASCD）胶体成像方法，形成了非饱和土壤胶体非均匀迁移全局性示踪方法。发展了非饱和土壤负压边界控制系统、研发了非饱和土壤胶体和溶质示踪剂原位连续测试方法，为非饱和土壤胶体迁移特性研究提供了真实的非饱和流场控制条件和原位连续监测方法。实验室和现场条件下，针对胶体非均匀迁移机理和模拟方法，开展了惰性溶质示踪剂-模拟胶体同步穿透实验、非均匀土壤介质-水流运动-溶质迁移-胶体输移连续背景解析实验、胶体非均匀迁移连续过程监测实验，揭示了非饱和条件下土壤介质性质和非线性流动特性对胶体迁移的影响机制、确立了变化含水率条件下胶体迁移特性与主控机制、构建了土壤介质-非均匀水流-溶质迁移-胶体非均匀迁移模式的映射关系、阐明了非均匀流动条件下胶体迁移的驱动机制和过程响应机理。发展了基于基质流区-优先流区的两区水流运动与胶体运动叠加的数值模型、基于水流-胶体非均匀模式映射关系的胶体迁移模型、以及基于活动性流场的胶体非均匀迁移模型，系统性的发展了基于介质条件和流动条件的胶体迁移数值模拟方法。通过广义势能和梯度特征了多因子耦合作用下的胶体迁移本构关系，与非线性流动特性相耦合，构建了具有完全物理机制的基于广义势能的胶体迁移模拟方法。相关研究在Journal of Hydrology等期刊发表SCI研究论文9篇，获得水利部大禹水利科学技术进步一等奖1项。相关成果对非饱和土壤节水增效和提升环境效益提供了重要的理论支撑。