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Abstract: 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 underlain 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 permeability 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.

This manuscript describes field measurement of gas permeability of a compacted loess that is proposed to be used as a final cover material for MSW landfill in Northwest China. The results provided by the authors are of interest to the researchers and practitioners from the field of landfill covers since the field experimental results of gas permeability of unsaturated loess have been rarely published in the literature. The experimental setup, instrumentation and procedure are provided in details. The authors do have some good descriptions and explanations of test results. However, a more in-depth interpretation of experimental data may help the readers to better understand the scale effect for field measurement as compared with laboratory measurement.

现场测试固废填埋场压实黄土覆盖层的气相渗透系数

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