大气-植被共同作用下土质覆盖层水气耦合运移规律及调控机理

Soil covers are widely used to control water and gas transfer between landfill waste and the atmosphere. However, the great majority of existing studies have been only focused on water transport in soil cover. To provide theoretical and methodological basis for the assessment and optimization of soil cover with respect to the ability of preventing water infiltration and gas emission, it is necessary to carry out an investigation on water-gas coupled transport in soil cover subject to combined actions from the atmosphere and plant and the corresponding co-conditioning mechanism. This project aims to develop a co-conditioning theory for water-gas coupled transport in soil cover and hence to promote the development of innovative soil cover. To realize the above objectives, the key is to establish a two-phase seepage mathematical model for unsaturated soils including root and to reveal interaction mechanism of water-gas coupled transport in soil cover and the corresponding co-conditioning mechanism. Laboratory tests, physical model tests, theoretical study and numerical modeling will be carried out in this study from view points of material properties and cover structure. In addition to enriching multi-field coupling seepage theory, the success of this project will also provide necessary theoretical and methodological basis for the design of co-conditioning water-gas coupled transport in landfill as well as guide the design of final cover system of landfill.

土质覆盖层广泛应用于调控填埋体与大气间的水、气传递，然而目前研究大多只侧重水分运移，深入研究其水、气耦合运移规律及调控机理才能为其防渗及闭气性能的评价及优化提供理论依据及设计方法。本项目拟发展土质覆盖层水、气联合调控理论，促进新型土质覆盖层的发展。为此，建立含根系非饱和土体水、气二相渗流数学模型，探索多场作用下土质覆盖层水、气运移的相互作用机理和水、气联合调控机理，是实现土质覆盖层防渗及闭气功能设计的关键和亟需解决的问题。本项目拟综合土单元及物理模型试验、数学模型和数值模拟手段，从材料特性和覆盖层结构两个层面上对大气-植被共同作用下土质覆盖层水、气耦合运移特性和调控机理展开系统深入研究，拟建立土质覆盖层水、气联合调控理论，发展具有防渗闭气功能的新型土质覆盖层。成果能丰富多孔介质多场耦合渗流理论，为填埋场水、气综合调控设计提供必要的理论依据及计算方法，指导填埋场封场覆盖系统的科学设计。

为了防止大气中的雨水进入垃圾体产生渗沥液，同时防止垃圾体降解产生的填埋气进入大气中，垃圾填埋场要求其顶部封场覆盖层具有很好的防渗闭气性能。大气条件和种植在覆盖层表面的植被对覆盖层的防渗闭气性能有重要影响，但其作用效果及作用机理还有待研究。本项目综合土单元、物理模型和现场试验、数学模型和数值模拟手段，从材料特性和覆盖层结构两个层面上对大气-植被共同作用下土质覆盖层水、气耦合运移特性和调控机理展开系统深入研究。研究结果表明，在材料特性层面上，含植根土具有比无植根土更强的持水能力；温度升高会导致含植根土的持水能力下降，非饱和水渗透系数增大；含植根土非饱和透气系数比无根土小，并且根系参数越大，含植根土的非饱和透气系数越小；在25-60℃温度范围内，含植根土的非饱和透气系数差异不明显。在结构层面上，相比于单层和双层毛细阻滞结构的含植被土质覆盖层，三层毛细阻滞结构的含植被土质覆盖层具有更强的防渗闭气性能；相比于无植被层和鸭脚木植被层，以草皮形式种植的狗牙根植被层可以在干旱条件使覆盖层表层土维持更高的含水率，从而维持覆盖层的闭气效果；覆盖层底部通气条件可减小雨水的下渗；对于带有坡度的覆盖层，应在坡顶处加强覆盖层的闭气性，在坡底处加强覆盖层的防渗性。本项目研究成果能丰富多孔介质多场耦合渗流理论，为填埋场水、气综合调控设计提供必要的理论依据及计算方法，指导填埋场封场覆盖系统的科学设计。