Research Initiation: Numerical Solution of Hazardous Waste Containment and Consolidation via Artificial Ground Freezing

这项研究调查了人工地面冻结作为控制和巩固危险废物的一种手段的使用。提出了一种土壤固化的二维有限元模拟方法。该数值策略利用创新的技术来表示树枝晶曲率、有限元网格部署以及数值热量和质量守恒。该凝固模型基于冻结相和非冻结相的耦合瞬变热和质量方程。边界条件考虑了界面能、动力学和溶质排斥效应。自适应有限元网格不断跟踪相前沿，从而直接在界面上应用边界条件。采用了自动重离散例程，在模拟过程中不需要用户干预。数值模拟将与现有的大规模实验数据进行比较，这些数据涉及土壤在有和没有氯化钠的情况下的固化以及添加了危险废物(氯仿、苯、甲苯和四氯乙烯)的土壤。人工冻土在土木工程中的应用已有一个多世纪的历史。它具有形成不透水屏障、脱水污泥和固结固体的能力。然而，对于任意几何形状，预测或控制作为时间函数的冻结屏障的位置是没有解决的。由于过冷和成分过冷，耦合的热质传递系统中存在着与枝晶生长相关的不稳定性。处理土壤固化的耦合传输系统不能修正为超出一维情况的解析解。因此，这项建议的研究具有很大的前景，可以为地面冻结的控制提供解决方案。

This research investigates the use of artificial ground freezing as a means of containing and consolidating hazardous waste. A two dimensional finite element simulation of soil solidification is proposed. The numerical strategy utilizes innovative techniques for representing dendrite curvature, finite element grid deployment and numerical heat and mass conservation. The solidification model is based on the coupled, transient heat and mass equations in both frozen and unfrozen phases. Boundary conditions account for the interfacial energy, kinetics and solute rejection effects. The adaptive finite element mesh continually tracks the phase front such that boundary conditions are applied directly on the interface. An automatic rediscretization routine is employed which requires no user intervention during the simulation. The numerical simulations will be compared to existing, large-scale experimental data for situations involving the solidification of soils with and without sodium chloride and soils spiked with hazardous wastes (chloroform, benzene, toluene and tetrachloroethylene). Artificial ground freezing has been in practice for over a century in civil engineering applications. Its ability to form impermeable barriers, dewater sludge, and consolidate solids has been demonstrated. However, predicting or controlling the location of the frozen barrier as a function of time for arbitrary geometries is unsolved. Inherent in the coupled heat and mass transfer system lie instabilities associated with the growth of dendrites due to undercooling and constitutional supercooling. The coupled transport system dealing with solidification of the soil is unamendable to analytical solutions beyond one dimensional situations. Consequently, this proposal research holds great promise if illuminating the solution to the control of ground freezing.