摘要
目的：我国西北地区黄土分布广泛，黄土作为当地固废填埋场的覆盖土料具有广泛的应用前景。现场尺度测试压实黄土覆盖层的气相渗透系数，从而可用于评估其填埋气减排性能。方法：1．在西安固废填埋场建立压实黄土覆盖层试验基地（图2）；2．在试验基地的膜内核心测试区域布置通气试验系统，包括空气压缩机、通气管网、气压测试装置、含水率测试装置、温度传感器和静态箱（图3，5～7）；3．在覆盖层表面裸露时和植草后分别进行通气试验测试压实黄土覆盖层的气相渗透系数。结论：1．当饱和度低于85％时，干密度为1．45Mg／m3压实黄土的气相渗透系数随含水率增加而降低，但并不明显；但是当饱和度高于85％时，气相渗透系数随含水率增加而显著减小；2．黄土层和碎石层之间的毛细阻滞作用使得上部黄土层储存更多水分，并显著降低其气相渗透系数，这有利于降低填埋气的排放；3．裸露条件下，当压实黄土的体积含水率从36％增加至46％时，其气相渗透系数从3．67×10-12m2降低至5．73×10-14m2；4．植草后压实黄土的气相渗透系数比裸露条件下小近一个数量级，这主要是因为植被根系占据了压实黄土的大孔隙；5．现场尺度的压实黄土气相渗透系数比室内试验的结果高1至2个数量级，这主要是因为现场所用黄土含有大的结团，结团会增加黄土的孔隙直径以及减小孔隙的曲折度。
The use of loess as an earthen final cover material is promising in northwest China which has an arid and semi-arid climate. A full-scale testing facility with an area 30 m long by 20 m wide was constructed at the Xi＇an landfill of municipal solid wastes to investigate the performance of an inclined capillary barrier cover. The cover consisted of a compacted loess layer un- derlain by a gravel layer. The testing facility was well instrumented for a gas permeation test and recording of the soil conditions in terms of volumetric water content, pore gas pressure, and soil temperature. Tests were performed to measure the gas permeability of the compacted loess before and after the planting of vegetation on the cover. The field measurements demonstrate that the capillary break at the fine/coarse soil interface allows the upper compacted loess layer to retain more water, and conversely reduces its gas permeability, which is favorable for reducing landfill gas emissions. When the degree of saturation of the compacted loess was greater than 85%, the gas permeability decreased significantly with a further increment in volumetric water content. The growth of vegetation roots tended to fill the large pores in the upper loosely-compacted loess, resulting in a decrease in gas per- meability of one order of magnitude. The influence of soil clods in the compacted loess on gas permeability can be one to two orders of magnitude due to an increase in pore size and a decrease in tortuosity.
基金
Project supported by the National Basic Research Program(973 Program)of China(No.2012CB719805)
