不均匀沉降作用下土质覆盖层防渗性能劣化机理及调控方法

Degradation of waste produces large differential settlements, causing cracks in landfill covers and thus deterioration on water infiltration. However, the great majority of existing studies have ignored the preferential flow induced by differential settlements. To provide theoretical and methodological basis for the assessment and optimization of soil cover with respect to the ability of preventing water infiltration subjected to differential settlements, it is necessary to carry out an in-depth investigation on water transport in soil cover subject to combined actions from the differential settlements and the corresponding co-conditioning mechanism. Based on the development and self-healing of cracks, this project aims to develop a co-conditioning theory for water transport in soil cover subjected to differential settlements and hence to promote the development of innovative soil cover. To realize the above objectives, the key is to obtain the water transport subjected to the self-healing of cracks and to reveal co-conditioning mechanism of water transport in soil cover and the corresponding co-conditioning mechanism. Laboratory tests, physical model tests and field tests will be carried out in this study from view points of the self-healing of cracks. In addition to enriching water seepage theory subjected to large deformation, the success of this project will also provide necessary theoretical and methodological basis for the design of water transport in landfill as well as guide the design of final cover system of landfill.

垃圾降解导致不均匀沉降显著，引发覆盖系统产生裂隙，造成防渗性能的劣化。然而目前研究大多忽略不均匀沉降引发的优势流，深入研究不均匀沉降下水分运移规律及调控机理才能为覆盖系统长期防渗性能的评价及优化提供理论依据及设计方法。本项目拟从不均匀沉降引发裂隙的发展和自愈合特性出发，发展不均匀沉降条件下水分运移理论，促进土质覆盖系统水分运移调控理论的发展。为此，探索不均匀沉降作用下土质覆盖系统水分运移规律，揭示裂隙自愈合变化规律及调控机理，是实现长期防渗功能设计的关键和亟需解决的问题。本项目拟综合单层土体试验、物理模型试验和现场试验，对不均匀沉降下土质覆盖系统的水分运移特性和调控规律展开深入研究，拟建立考虑裂隙自愈合特性的水分运移调控理论，发展具有长期防渗性能的土质覆盖系统设计方法。成果能丰富大变形多孔介质渗流理论，为填埋场水分运移调控设计提供必要的理论依据及计算方法，指导填埋场覆盖系统的科学设计。

垃圾降解导致不均匀沉降显著，引发覆盖系统产生裂隙，造成防渗性能的劣化。然而目前研究大多忽略不均匀沉降引发的优势流，深入研究不均匀沉降下水分运移规律及调控机理才能为覆盖系统长期防渗性能的评价及优化提供理论依据及设计方法。本项目从不均匀沉降引发裂隙的发展和自愈合特性出发，发展不均匀沉降条件下水分运移理论，促进土质覆盖系统水分运移调控理论的发展。为此，探索不均匀沉降作用下土质覆盖系统水分运移规律，揭示裂隙自愈合变化规律及调控机理，是实现长期防渗功能设计的关键和亟需解决的问题。本项目综合单层土体试验、物理模型试验和现场试验，对不均匀沉降下土质覆盖系统的水分运移特性和调控规律展开深入研究。研究发现，不均匀沉降促使土层出现贯穿整个土层的裂隙，形成雨水入渗的优势通道，导致雨水入渗速率增加。当不均匀沉降量为7.5cm时，毛细阻滞覆盖系统的击穿时间缩短了1h，粗粒土层的侧向导排量增大了38%，说明沉降量较小时，粗粒土层依然具有良好的侧向导排性能。粘土层平均渗透系数增大了两个数量级，最终产生下渗量为25.8mm。当不均匀沉降量为22cm时，粘土层的防渗性能进一步劣化，平均渗透系数增大为1.7×10-6m/s，下渗量增大至89.9mm。当产生不均匀沉降时（22cm），降雨时间对水分运移的影响较大，降雨历时12h的粗粒土侧向导排量比降雨历时4h增大4.1倍，降雨历时12h的渗漏量比降雨历时4h增大113%。而倾斜角度对不均匀沉降条件下覆盖系统水分运移影响较小，这主要由于不均匀沉降引发的裂隙是雨水下降的主要优势通道，倾斜角对优势通道内的水分运移影响较小，因此覆盖系统倾斜角应设计为规范最大值。根据这些调控指标设计的三层覆盖系统在湿润气候下（深圳）运营1年，水分运移规律和模型试验相似，累计下渗量为12mm，小于EPA规定的允许下渗量，说明不均匀沉降条件下三层覆盖系统的防渗性能仍符合要求。本项目成果能丰富大变形多孔介质渗流理论，为填埋场水分运移调控设计提供必要的理论依据及计算方法，指导填埋场覆盖系统的科学设计。