摘要
目的：为更好地评价填埋场覆盖层系统的闭气性能，建立水气耦合条件下的覆盖层中气体运移模型。在此基础上分析大气压强波动、渗透系数变化和对流扩散等因素耦合作用下填埋气在覆盖层中的运移规律。创新点：建立水气耦合条件下填埋气在覆盖层中的运移模型，分析多种因素耦合作用下填埋气的运移过程，并比较对流运移和扩散运移的相对重要性。方法：1．通过理论分析，建立考虑压强、对流、扩散和非饱和情况的填埋气耦合运移模型；2．通过试验拟合，得到大气压强波动的拟合经验公式（公式（22）），构建考虑压强波动下填埋气多场耦合运移模型；3．通过仿真模拟，验证所建模型的可行性和正确性（图2），并分析包含大气雎强波动和渗透率等影响因素作用下填埋气的运移规律（图6～8）。结论：1．覆盖层厚度从1米变化到2米，覆盖层中填埋气的浓度变化可达31％；2．对于受大气压强波动影响较大的覆盖层系统（如1×10^3Pa），不能忽略压强波动对填埋气运移的影响；3．气体渗透系数在初期对气体运移有较大影响，随运移时间增加直至气体运移达到稳定状态，渗透牢的影响可以忽略（仅3％）。
Cover systems are used to prevent water infiltration into a waste body. They also play an important role in controlling landfill gas transport from the waste body to the atmosphere. It is important to assess the flux of landfill gas at the surface of a cover system by considering the coupled effects of rainwater infiltration and gas transport in the cover soils. We have developed a 1D mathematical model for coupled transient gas and water transport in unsaturated cover soils. The coupled model was solved by the finite element method. Results obtained by the proposed model agreed well with experimental data. Based on the proposed solution, the influences of gas pressure, gas permeability, and the thickness of the cover soils on soil gas concentration profiles were investigated. The difference in soil gas concentration reached up to 31% as the thickness of cover increased from 1 to 2 m. Gas concentration at a depth of 0.2 m decreased by 6% as the amplitude of atmospheric gas pressure fluctuation increased from 20 to 100 Pa. The gas concentration increased by only 3% when gas permeability increased by a factor of 2 for a relatively long period of gas migration （e.g., 60 h） under the given conditions. Results suggest that both diffusion and advection should be considered when estimating gas transport in unsaturated cover soils. The numerical model can be used in the design of cover systems in relation to gas breakthrough time, breakthrough concentration, and flux.
基金
Project supported by the National Basic Research Program of China(973 Program)(No.2012CB719806)
the National Natural Science Foundation of China(Nos.51478427,51278452,51578356,51508508,and 51008274)
the Fundamental Research Funds for the Central Universities(No.2014QNA4019)
the Natural Science Foundation of Zhejiang Province(No.LY13D060003)
Zhejiang Provincial Public Industry Research Project(No.2015C31005),China
关键词
填埋气
覆盖层系统
非饱和土
气水运移
耦合模型
Landfill gas, Cover systems, Unsaturated soils, Gas-water transport, Coupled model
