特殊地下水环境中化学淤堵的细观机理及其数学模拟研究

Chemical clogging is a common phenomenon in groundwater engineering, such as tailings dam, landfill, etc. Because it could change the permeability characteristics of soil-rock media and affect the safety and stability of engineering, chemical clogging has become a hotspot and difficulty in research of groundwater science. In order to reveal the micro-mechanism of chemical clogging and present the preparedness plans, this study would research the chemical clogging of tailings sand and garbage soil by combining site investigation and sampling, laboratory-scale column experiments, nuclear magnetic resonance (NMR) and mathematical model. It would analyze the change rule of pore structure, porosity, permeability, concentration, etc. It would reveal the mechanism of chemical clogging in the groundwater environment. Based to the transition state theory and Kozeny-Carmen equation, it could determine the type，path and condition of chemical reaction in tailings sand and garbage soil. Then, while the coupling relationship among chemical reaction, porosity, permeability coefficient and time would be obtained, the coupling model between groundwater flow and solute transport should be built in special groundwater. The method of numerical solution also is developed. The reliability and parameters sensitivity of the model is analyzed in order to provide theory basis for scientifically managing the special groundwater resources.

化学淤堵是尾矿库、垃圾填埋场等特殊地下水环境中常见的一种现象，其以改变岩土体介质的渗透特性、影响工程安全运行而成为地下水科学与工程领域研究的热点和难点。为进一步从细观角度揭示多孔介质中化学淤堵的发生机理，提前做出防治预案，本项目拟采用现场调研、室内柱试验、核磁共振细观无损测试和数值模拟相结合的方式，对以尾矿砂和垃圾土为代表的地下水介质中化学淤堵现象进行研究。分析地下多孔介质的孔隙结构、孔隙率、渗透系数、溶质浓度的变化规律，揭示地下水环境中化学淤堵的发生机理；基于过渡态理论和Kozeny-Carmen方程，确定引起尾矿砂和垃圾土等多孔介质发生淤堵的化学反应类型、条件、路径，构建化学反应-孔隙率-渗透系数-时间之间的相互关系，建立特殊地下水环境中地下水流与溶质迁移耦合模型，开发数值求解算法，并对模型可靠性、参数敏感性进行分析。为进一步科学管理特殊环境中的地下水资源奠定理论基础。

淤堵是尾矿库、垃圾填埋场等特殊地下水环境中常见的一种现象，其以改变岩土体介质的渗透特性、影响工程安全运行而成为地下水科学与工程领域研究的热点和难点。本项目基于现场调研，对调研样品进行物理和化学特性分析，发现尾矿粒径为0.25-0.5mm的砂粒占比44%-58%，为粒径的主要成分,尾矿砂表面主要含氧元素和硅元素，渗滤液中Fe2+离子浓度较大，为化学淤堵的发生提供了条件,垃圾龄期与腐殖质土含量成正比关系；开展室内渗透破坏试验，利用核磁共振技术，分析不同细粒尾矿砂在渗流条件下的孔隙变化规律,结果表明，沿渗流方向，颗粒损失和上限粒径均减小，砂样下部以大孔径为主，上部微孔和中孔占比较大；基于核磁共振装置设计试验模拟细粒尾矿渗透破坏进程，发现随着侵蚀时间的增加，孔隙范围越来越窄，孔隙率越来越大，大孔径分布越来越集中；建立考虑化学淤堵的尾矿坝数值模型进行渗流计算，结果显示淤堵作用下浸润线均有上升，坝体内水位雍高；对栗西尾矿库增设简化辐射井之后的渗流场进行数值模拟，在相同干滩长度下，浸润线高度整体趋势降低，坝坡溢流情况得到明显改善；选取垃圾填埋单元为研究对象，提出一种考虑非均质渗透特性和堆填过程的渗流模型建立方法，建立导排层淤堵模型并进行瞬态渗流场分析，结果表明降雨强度增大，导排层淤堵，中间覆盖层渗透性降低均可引起垃圾填埋场滞水位的升高。