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

本研究调查了使用人工地面冻结作为一种手段，包含和巩固危险废物。提出了一种土体凝固的二维有限元模拟方法。数值策略利用创新技术来表示枝晶曲率，有限元网格部署和数值热量和质量守恒。凝固模型是基于冻结阶段和未冻结阶段的耦合瞬态热量和质量方程。边界条件考虑了界面能、动力学和溶质排斥效应。自适应有限元网格连续跟踪相阵，使边界条件直接作用于界面上。采用了一种自动再离散程序，在仿真过程中无需用户干预。数值模拟将与现有的大规模实验数据进行比较，这些数据涉及有氯化钠和没有氯化钠的土壤的凝固情况以及含有危险废物（氯仿、苯、甲苯和四氯乙烯）的土壤。人工冻结在土木工程中的应用已有一个多世纪的历史。其形成不透水屏障，脱水污泥和巩固固体的能力已被证明。然而，预测或控制冻结势垒的位置作为任意几何的时间函数是没有解决的。耦合传热传质系统中固有的不稳定性与过冷和过冷引起的枝晶生长有关。处理土壤凝固的耦合输运系统在一维以外的情况下不能得到解析解。因此，这一建议的研究对于阐明控制地面冻结的解决方案具有很大的希望。

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.