基于线性吸附效应的CCL非饱和渗透特性

Unsaturated permeability of compacted clay liner under linear adsorption conditions

摘要:

压实粘土衬垫（CCL）作为卫生填埋场最主要的防渗措施，其主要组成成分的粘性土体，在阻渗过程中会吸附渗滤液中的污染物质，改变土体孔隙结构，显著影响CCL防渗性能。假定CCL土体对污染物的吸附服从线性模式，土中孔隙均匀分布，土孔隙体积的改变只受污染物吸附效应影响，基于质量和体积关系分析，建立考虑污染物吸附效应的非饱和渗流模型，采用数值方法分析了CCL对污染物的吸附效应对其非饱和渗透系数的影响。结果表明，填埋场CCL对污染物的吸附作用可有效降低防渗系统孔隙率，显著提高CCL防渗性能。在考虑吸附效应条件下，吸附分配系数、污染物浓度、初始孔隙率和有效饱和度等参数对CCL非饱和渗透性能有较大影响。研究成果为科学选择CCL材料、优化填埋场CCL设计、确保生活垃圾处置安全提供了理论依据。

Abstract:

The compacted clay liner (CCL), the main anti-seepage facilities in landfill and generally made up of clayey soil, will adsorb the contaminants of the leachate when it prevent the leachate from polluting the groundwater and surrounding soils. The permeability of the CCL is affected by its microscopic pore structure changes due to the adsorption of clay. It is assumed that the adsorption of contaminants on the CCL is in accordance with the linear model, the pore distribution in the CCL is uniform and it is only affected by the adsorption. Based on the conservation of volume and mass, an empirical formula was presented for CCL to evaluate the changes of porosity induced by the adsorption. Meanwhile, a new unsaturated permeability model was also suggested considering the adsorption effects of contaminants on the CCL pore structure. Finally, the effects of adsorption of CCL on its unsaturated permeability were analyzed by numerical calculation. The results show that the adsorption of contaminants on CCL can reduce the porosity and improve the performance of seepage-prevention of CCL. Taking the adsorption effects into account, the unsaturated permeability of the CCL is significantly affected by the adsorption distribution coefficient, contaminant concentration, initial porosity and effective saturation. The studies may be helpful to the selection of materials of CCL, provide theoretical references for designing of CCL, and ensure the safe disposal of municipal solid waste.