垃圾填埋场毛细阻滞型腾发封顶模型试验

Model test of a capillary barrier evapotranspiration cover for landfills

作为替代型垃圾填埋场封顶,毛细阻滞型腾发封顶具有诸多优点,但目前主要在欧美干旱、半干旱地区使用,对其在湿润气候区工作性能的研究较少。选用低塑性粉质黏土和砾砂作为填料,在杭州市一露天环境构筑模型土柱并培育植被,量测自然降雨、蒸发和植被蒸腾作用下土柱透水量、地表径流量和各深度含水率变化,探讨毛细阻滞型腾发封顶的工作机制。试验历时15个月,得到该封顶在降雨高峰期、晴热高温期、台风影响期和冬季阴冷期等时段的响应。试验结果表明,降雨和腾发作用下粉质黏土含水率变化较大,底部砾砂中也有较小幅度干湿循环,腾发可在整个封顶土层范围内起作用;当粉质黏土底部达到饱和,砾砂含水率接近4%时底部有水透出,此时该封顶暂时失效,后随水汽运移毛细阻滞界面功能恢复,该封顶仍能正常工作;试验过程中,降雨总量为1 782.6 mm,共产生地表径流为53.08 mm,透水为19.64 mm,其他降水均在土层吸持与腾发交替作用下最终返回大气,在试验期间该封顶能有效地阻止降雨入渗。

Capillary barrier evapotranspiration covers have many advantages over conventional covers. But they are mainly used in arid or semi-arid areas in USA and Europe. Whether they can be used in humid areas remains to be determined. Using low plastic silty clay and gravelly sand as material, a soil column is constructed in outdoor environment in Hangzhou and vegetation is planted. Water content, percolation and surface runoff are measured. Peak rainfall season, sunny and hot season, typhoon period and winter season are experienced during the monitoring 15 months. Results show that volumetric water content of silty clay changes greatly under natural infiltration and evapotranspiration; the and small dry-wet cycles exist in gravelly sand. It is shown that evapotranspiration acts on the whole depth of the cover. There comes percolation when silty clay in the bottom becomes saturated and volumetric water content of gravelly sand approaches 4%. The cover becomes temporarily ineffective and will soon be effective again when water content decreases due to vapor movement. Rainfall, surface runoff and percolation are 1 782.6, 53.08, 19.64 mm respectively. Most rainfall are stored in soils and later returned to the atmosphere by evapotranspiration. The cover can prevent percolation effectively during the test period.