降解、压缩和干湿循环耦合作用下垃圾持水特性及填埋场液气导排控制研究

Municipal solid waste (MSW) landfills in China face the problem of low efficiency in leachate drainage and landfill gas (LFG) collection. This is resulted by the formation and variation of unsaturated, saturated and gas-filled dry zones in landfills. Landfilled MSWs undergo coupled processes of biodegradation, compression and liquid-gas flow. It is difficult for liquid-gas flow modeling to determine the unsaturated, saturated and gas-filled dry zones in landfills without considering bio-hydro-mechanical coupled effects on the change of water retention properties for MSWs. This project will study the relationship of particle size and inner-particle moisture content with the degree of biodegradation for MSWs through laboratory experiments. Soil-water characteristic curves (SWCC) of MSWs with different degrees of biodegradation and compression will be tested under drying-wetting cycles. The effect of suction change on waste deformation will be assessed. The effects of particle-size, void ratio and hysteresis on water retention properties of MSWs will be studied, and a hysteresis model will be established to assess the increment of saturation during the bio-hydro-mechanical coupled processes. The governing equations for liquid-gas flow as well as the corresponding program of a bio-hydro-mechanical (BHM) coupled model proposed by the applicant will be updated through the hysteresis model. The formation and variation of typical liquid-gas zones in Chinese landfill will be studied through the BHM coupled model. Optimization methods for the design and operation of leachate drainage and LFG collection systems will be developed.

我国城市垃圾填埋场液气存在形式复杂，垃圾体存在非饱和区、饱和区及封闭气包区，这些区域的形成以及不断发展和变化是我国填埋场液气导排难以有效实施的根本原因。填埋场垃圾受到降解、压缩和渗流的耦合作用，未考虑耦合作用下垃圾持水特性的变化导致目前液气耦合运移分析无法揭示填埋场典型液气存在形式。本项目通过室内试验揭示固相颗粒尺寸及胞内水含量与降解程度的相关关系；在此基础上开展降解-压缩耦合作用下不同饱和度路径垃圾土水特征曲线测试，分析基质吸力对垃圾变形的影响，揭示降解、压缩和干湿循环耦合作用过程中固相颗粒尺寸和孔隙比变化以及干湿滞回效应对垃圾持水特性的影响规律，建立降解、压缩和干湿循环耦合作用下垃圾饱和度增量计算模型，并对已有固-液-气耦合作用模型的渗流控制方程和相应的数值分析程序进行更新；针对我国填埋场工程特点，分析填埋场典型液气存在形式的形成、发展和变化规律，提出液气导排系统设计和运行优化方法。

开展城市生活垃圾持水特性研究对于填埋场液气存在形式分析及液气导排系统设计和运行优化具有非常重要的意义。通过人工配制新鲜样的室内降解试验，获取不同降解程度垃圾试样。测试了垃圾试样的降解程度表征指标C/L和DOD、固相颗粒颗分曲线和比重。提出吸水纸法结合烘干法测试垃圾试样胞内水含量，并通过室内试验验证了方法的可靠性，发现2个月内胞内水基本释放完毕。提出了考虑降解的颗分曲线计算模型，该模型能够较好地预测不同降解龄期下垃圾试样的颗分曲线。研制了大尺寸城市生活垃圾骨架和孔隙水体积变化系数测量装置，利用该装置测试了新鲜状态和2个月降解龄下各3个不同孔隙比试样的土水特征曲线，分析得到了孔隙比和降解对垃圾持水特性的影响规律。提出了基于颗分曲线和孔隙比的土水特征曲线预测模型，该模型较好的预测了2个月降解龄垃圾试样和高龄期钻孔试样的土水特征曲线，且所预测得到的土水特征曲线能够较好地反映孔隙比和降解对于垃圾持水特性的影响规律。通过上述试验确定了垃圾骨架和孔隙水体积变化模型参数的取值。开展了不同降解程度垃圾试样渗透系数的室内试验，建立了考虑降解-压缩耦合作用的渗透系数计算模型。建立了考虑优先流和基质流的填埋场竖井降水模型，获得了渗沥液水位降深的解析解。更新了已有固-液-气耦合模型和分析程序，针对我国高水位填埋场，分析了两个填埋场的现场竖井抽水试验，建议降水设计时wf和kfr/kmr的取值分别为0.45和500；分析了中型和大型填埋场填埋气收集率与渗沥液水位的相关性，建议渗沥液水位控制在填埋厚度的30%以下，以确保填埋气收集的有效性。