MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering, Department of Civil Engineering, Zhejiang University, Hangzhou 310058, China.
MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering, Department of Civil Engineering, Zhejiang University, Hangzhou 310058, China.
Sci Total Environ. 2020 May 20;718:137195. doi: 10.1016/j.scitotenv.2020.137195. Epub 2020 Feb 8.
Loess is widely distributed in Northwest China where the rainy season coincides with the warm and vegetation growth period. The use of loess as a capillary barrier cover (CBC) material is promising. However, how the loess/gravel CBC perform as a capillary barrier and landfill gas emissions controller remains elusive. In this study, the performance of a designed CBC comprised 1.3 m-thick compacted loess underlain by 0.3 m-thick gravel in extremely wet and dry years of Xi'an city from 1950 to 2000 was analyzed using numerical modeling. An instrumented CBC test section comprised 0.9 m-thick compacted loess underlain by 0.3 m-thick gravel was constructed to show the hydraulic responses in real conditions from January 2015 to January 2017. The numerical results indicated that the designed CBC performed well as a capillary barrier as no percolation occurred during the extremely wet periods. Despite adopting a CBC of 0.4 m thinner than the designed one, the test section produced only 16.16 mm percolation during the two-year monitoring period, and that can meet the recommended limit of 30 mm/yr. The effect of the capillary break on increasing the water storage within the CBC was observed at the test section in fall. The increased water storage can significantly decrease the gas permeability, and thus improve the performance of the CBC as a LFG emissions controller. Furthermore, the LFG emissions can be controlled to meet the limit set by the Australian guideline by decreasing the bottom gas pressure and artificial watering. Finally, a procedure was proposed to enhance the performance of CBCs.
黄土广泛分布在中国西北地区，该地区的雨季与温暖和植被生长期相吻合。因此，将黄土用作毛细屏障覆盖（CBC）材料具有广阔的应用前景。然而，黄土/砾石 CBC 作为毛细屏障和垃圾填埋气排放控制器的性能仍不清楚。在本研究中，采用数值模拟的方法，分析了 1950 年至 2000 年西安地区极端湿润和干燥年份中，1.3m 厚压实黄土下 0.3m 厚砾石作为 CBC 的性能。在 2015 年 1 月至 2017 年 1 月的实际条件下，通过建造一个 0.9m 厚压实黄土下 0.3m 厚砾石的 CBC 测试段来展示其水力响应。数值结果表明，设计的 CBC 作为毛细屏障表现良好，因为在极端湿润期间没有渗流发生。尽管采用的 CBC 比设计的 CBC 薄 0.4m，但在两年的监测期间，测试段仅产生了 16.16mm 的渗流，这可以满足建议的 30mm/yr 的限制。在测试段，观察到毛细断裂对增加 CBC 内储水的影响。增加的储水量可以显著降低气体渗透性，从而提高 CBC 作为垃圾填埋气排放控制器的性能。此外，可以通过降低底部气压和人工浇水来控制垃圾填埋气排放，以满足澳大利亚指南规定的限制。最后，提出了一种提高 CBC 性能的方法。
