填埋场防渗垫层服役性能数值模型研究

Numerical study on performance of anti-seepage liner of landfills

防渗垫层是卫生填埋场的有机组成部分,是阻止渗滤液污染物运移扩散的重要屏障。针对中国填埋场中常用的4种典型单层衬垫结构形式,选用渗漏量、溶质通量及吸附量作为评价指标,建立数值模型对垫层的防污性能进行对比研究。选择镉离子和苯作为填埋场渗滤液中重金属离子和有机污染物的典型代表。结果表明复合衬垫对重金属离子的防污性能显著优于单层压实黏土衬垫;在低渗滤液水头条件下,土工聚合膨润土(GCL)复合衬垫与压实黏土复合衬垫的防污性能接近,但随着渗滤液水头的增大,土工聚合膨润土复合衬垫的防污性能显著优于压实黏土复合衬垫。对有机污染物,综合考虑其通过完整土工膜的弥散过程及通过土工膜缺陷的渗漏过程,结果表明复合衬垫的最主要通道,衬垫底部有机物通量要比重金属离子通量大1～5个量级,土工聚合膨润土复合衬垫对有机物的防污性能最差。渗漏量、溶质通量及吸附量等指标能对大范围、长服役周期内垫层的防污性能做出科学合理的评价,相关结果能为防渗材料的比选及衬垫结构的设计及优化提供参考。

Anti-seepage liner plays an important role in modern landfills as the main structure preventing the landfill leachate from polluting environment.Four typical liner structures frequently used in Chinese landfills are analyzed,and three indexes,including leakage rate,mass flux and sorption capacity,are employed to evaluate the performance of liners.Cadmium and benzene are chosen as the typical inorganic and organic pollutants in leachate.The defects of geomembrane are the main pathway of inorganic pollutants,and the results show that performance of single CCL liner is much worse than that of the composite liner due to the excellent obstruction ability of geomembrane.The performances of GM+CCL composite liner and the GM+GCL composite liner are close with a low leachate head,but the GM+GCL composite perform better when the leachate head reaches a high value(eg.10 m).As to organic pollutant,the leakage through the geomembrane defects and the diffusion through the geomembrane itself are both considered.The results show that the mass flux of benzene at the base of liner is 1~5 magnitude higher than that of Cadmium,and the GM+GCL composite liner provides a minimum defense to the organic pollutant due to its lowest thickness.The evaluating indexes using here are proved to be able to provide reasonable and scientific assess to the large-scale and long-term performances of the landfill liner.The proposed methods and results can contribute to a better design or refining of landfill liner.