生活垃圾填埋场终场覆盖层的主要功能是防渗。部分湿润气候区因降雨量较多、土层储水能力不足,毛细阻滞覆盖层防渗效果不佳。在毛细阻滞覆盖层中添加非饱和导排层(unsaturated drainage layer,UDL)是改善毛细阻滞覆盖层在湿润气候区防渗性能的措施之一。开展室内模型试验对毛细阻滞覆盖层中UDL的侧向排水作用进行了实测和验证,对影响UDL侧向导排长度的因素进行了数值分析。模型试验尺寸为2.0 m×1.0 m×0.4 m(长×宽×厚),结构剖面从上至下依次为粉土层(20 cm)、砂层(10 cm)和碎石层(10 cm)。试验结果表明:累计降雨量为882.2 mm,UDL侧向导排水量为9.5 mm,占土层入渗水量的13.7%,水分侧向导排作用可观。UDL侧向导排长度影响因素数值分析结果表明:①细粒土厚度和渗透性对导排长度的影响因降雨量而异,当降雨量较小时,细粒土层越厚、渗透性越低,侧向导排长度越长;②UDL厚度对水分侧向导排长度影响不明显;③UDL进水值越低,细粒土储水能力越大,细粒土侧向导排失效时间和UDL侧向导排介入时间越晚,但持续降雨后期导排长度衰减速度更快,进水值须根据当地降雨条件和覆盖层粗、细粒土水力特性综合考虑。
Abstract
Seepage prevention is the main function of final cover of municipal solid waste landfill. Capillary barrier cover is not effective in some humid climates due to inadequate water holding capacity of soil. Adding unsaturated drainage layer (UDL) to the capillary barrier cover (CBC) is one of the measures to improve the performance of CBC in humid climate area. In this research, the lateral drainage performance of the capillary barrier cover with unsaturated drainage layer (CBC+UDL) was studied by combining indoor extreme rainfall model test and numerical analysis. Size of the cover model is 2.0 m×1.0 m× 0.4 m (length × width × thickness). The structural section from the upper to the lower is silt layer (20 cm), sand layer (10 cm), and gravel layer (10 cm) in sequence. The results of model test revealed that in the presence of 882.2 mm cumulative rainfall, the lateral drainage of UDL was 9.5 mm which accounted for 13.7% of the rainfall infiltration. Numerical simulation demonstrated that the effect of thickness and permeability of fine-grained soil on drainage length varied with rainfall amount: in the presence of small rainfall amount, a thicker fine-grained soil layer resulted in lower permeability and longer lateral drainage length. The thickness of UDL had little impact on the length of lateral drainage. A lower water entrance value of UDL would enhance the water storage capacity of fine-grained soil, and delay the failure of fine-grained soil and the effect of UDL. Nevertheless, the decay of drainage length in the late stage of continuous rainfall would accelerate. Therefore, the water entrance value of UDL must be considered comprehensively according to local rainfall conditions and hydraulic characteristics of coarse and fine grained soil covers.
关键词
毛细阻滞覆盖层 /
非饱和导排层 /
导排长度 /
渗透性 /
垃圾填埋
Key words
capillary-barrier cover /
unsaturated drainage layer (UDL) /
lateral drainage length /
permeability /
solid waste landfill
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基金
贵州省科技计划基础项目(黔科合基础1079,黔科合基础1513-4);国家杰出青年科学基金项目(51625805);贵州省科技厅社发攻关项目(黔科合SY字3055);中建四局科技研发项目(CSCEC4B-2015-KT-03)
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