垃圾填埋场覆盖屏障气体运移特性与长期服役性能评价方法

Compared to the hydraulic conductivity of the landfill cover barriers, the gas permeability and diffusivity of the barriers have not been investigated in detail.The currently design of the landfill cover barriers is limited to the requirement of the hydraulic conductivity of the barriers.This cannot meet the requirement of landfill gas pollution control and gas recycling. This project aims to investigate the mechanism of landfill gas transport in the three cover barriers, i.e., compacted clay soil, geomembrane, and the geosynthetic clay liner (GCL).Different combinations of gas pressure, temperature and gas concentration will be considered in the laboratory studies. The mathematical model will be developed for gas permeability and diffusion coefficient regarding the main factors. The variation of the gas permeability and diffusion coefficient with the factors, such as gas pressure, soil gas content and soil porosity will then be investigated. The effect of long-term rainfall infiltration, wet-dry cycles and the differential settlement on the performance of the three typical landfill cover systems will be investigated in the large geotechnical centrifuge. On the basis of the findings of the column test and the centrifuge test, a coupled model for landfill gas transport through cover barriers considering the effect of atmospheric pressure, seepage and temperature will be developed. The model will be numerically solved and the evaluation method will be proposed for the assessment of the long-term performance of the landfill cover barriers. The rational types of the landfill cover barriers will be proposed on the basis of the long-term performance analysis. The research work of this project is of great importance to pollution control and recycling of the landfill gas. The research work will also be of great importance to the rational design of sanitary landfills.

与覆盖屏障的水力传导特性相比，人们对填埋气在覆盖防渗层中的运移机理还缺乏深入的认识；目前仅采用水力传导特性进行填埋场覆盖屏障的设计，无法满足填埋气污染控制和资源化利用的要求。本课题在控制压力、温度、气体浓度等条件下，通过室内土柱试验研究填埋气在压实粘土、土工膜和GCL等覆盖防渗层中的运移特性，建立气体渗透率、扩散系数与主要影响因素之间的数学模型，分析覆盖防渗层中气体运移参数的变化规律；通过大型土工离心模型试验揭示长期降雨入渗、干湿循环和不均匀沉降等作用下三种典型防渗层的劣化机理；在此基础上，建立大气压力、渗流和温度耦合作用下填埋气通过防渗层的运移模型，并通过数值方法进行解答，获得防渗层长期服役性能的评价方法。在此基础上针对不同气候条件获得合理的屏障结构型式。本课题的研究对现代卫生填埋场气体的污染控制和资源化利用，以及对现代卫生填埋场的科学设计都有重要的工程意义和理论价值。

我国填埋场垃圾组分复杂， 其中的有机质降解产生大量的气体。这些气体的主要成分是甲烷和二氧化碳，亦含有种类很多的臭气如氨气和硫化氢，以及大量的挥发性有机物如芳香族类气体。我国填埋气对周边大气环境污染严重，覆盖层是防止填埋气进入大气环境的重要屏障。本项目针对不同气候和覆盖层特征，对土质覆盖系统和土工膜覆盖层性能开展了系统的研究工作，已完成各项计划任务，达到了预期目标。通过单元体试验、模型试验、离心机试验、现场试验和数值模拟等多尺度研究手段，分析了优势流产生的规律，揭示了土质覆盖系统的液气击穿机理，建立了填埋气在非饱和覆盖系统的耦合运移模型，提出了土质覆盖系统填埋气扩散量、气体击穿时间和甲烷氧化等计算方法，为既有填埋场填埋气的污染评估提供了依据。获得了挥发性有机物在填埋场复合屏障中的运移解析模型，在此基础上对我国规范规定的3种覆盖层结构防气体扩散的性能进行了比较，为填埋场覆盖屏障的设计提供了依据。建立了土工膜临时覆盖层甲烷浓度的测试方法，获得了填埋场表面甲烷浓度的长期监测数据，为土工膜覆盖层性能的评估提供了可靠的方法；同时，本项目还结合离心机试验、现场试验和数值模拟结果，提出了兼有防渗和气体减排等功能的覆盖系统设计方法和覆盖层长期服役性能的评估方法，为实现填埋气的污染控制提供了科学依据。共发表及录用学术论文21篇，其中SCI期刊论文13篇，EI收录论文7篇；授权发明专利1项；研究成果获2015年上海市科技进步二等奖1项；培养博士生6名，硕士生7名。