【作者】 贾官伟；

【导师】 陈云敏； 詹良通；

【作者基本信息】 浙江大学 ， 岩土工程， 2010， 博士

【摘要】 固废堆场终场覆盖系统担负着减少雨水下渗以减少渗滤液产量和防止堆场中有害气体无组织释放的重任,土质覆盖层(Alternative Earthen Final Cover)由天然非胀缩土料组成、具有良好的耐久性,其造价及后期维护费用远低于传统复合型覆盖层,是进行填埋场终场覆盖的理想结构型式。目前我国许多城市的固体废弃物填埋场已经达到或接近使用年限,面临封场覆盖问题；土质覆盖层中水分的运移规律和调控方法也尚未明确,因而开展对土质覆盖层的研究具有重要的现实意义和理论意义。本文以国家自然科学基金面上项目“湿润气候区土质覆盖层-大气水分传递机理及控制方法”(50878194)为依托,通过数值模拟、模型试验、解析法等手段系统研究了固体废弃物填埋场土质覆盖层内的水分运移规律,探讨了覆盖层内水分的调控方法。本文所做的主要工作和相应的研究成果如下：(1)采用Gitirana(2005)的降雨入渗-产流边界处理方式,研究了湿润气候区降雨雨型对土质覆盖层地表入渗量的影响。研究结果表明,在日降雨量和初始条件相同时,对非均匀雨型,雨强峰值出现越早则其总入渗量越大；在部分工况下,前锋型(A1)的地表入渗量会大于均匀雨型；短历时强降雨的入渗量明显较全天降雨的雨型小；在研究湿润气候区长期气候条件下土质覆盖层服役性能时若不采用实时气象资料则均匀雨型和前锋型(A1)雨型是最保守的设计雨型。(2)基于非饱和渗流控制方程,采用指数方程描述非饱和土体的土水特征曲线和渗透系数随含水量的变化,建立降雨入渗条件下无限长斜坡内水分运移模型并求得解析解,将解析结果与数值模拟结果进行对比验证了解析解的正确性,通过此解析解分析了土性参数、前后期雨强及坡度等因素对覆盖层内水分运移和存储规律的影响。最后,利用从解析解得到的基质吸力剖面分析了土质覆盖层在降雨条件下的稳定性变化。研究表明土质覆盖层饱和渗透系数越小,则湿润锋前进速度越慢,入渗水分易滞留在表层；减饱和系数越大,则表层含水量变化大,入渗影响深度浅；持水能力越强则相同时间内湿润锋影响深度越浅；对于毛细阻滞型覆盖层,细粒层中的含水量和基质吸力变化大,而粗细粒层界面以下的粗粒层中含水量变化很小。(3)自制由模型槽、降雨模拟装置、侧向排水与深层渗漏收集及量测装置、基质吸力和动态图像采集系统组成的模型试验装置,研究了湿润气候区强降雨条件下毛细阻滞覆盖层与大气间的水分传递规律及强降雨条件下设置非饱和导排层(Unsaturated Drainage Layer, UDL)时毛细阻滞覆盖层的性状,通过数值手段对试验结果进行了模拟研究。研究结果表明,在湿润气候区的强降雨条件下覆盖层表面的地表径流占到降雨总量的69%-77%,砂土非饱和导排层可以很好地发挥侧向排水作用疏干覆盖层内的水分,表层粉土饱和渗透系数越小则侧向导排量与深层渗漏量之比越大。(4)建立综合考虑填埋体和终场土质覆盖层的数值模型,研究了湿润气候区长期持续降雨天气下降雨雨强、降雨分配模式、UDL层厚度、粉土层厚度和渗透系数、覆盖层坡度等对覆盖层侧向导排(Lateral Diversion)能力的影响规律。研究结果表明,UDL层可大大提高普通毛细阻滞覆盖层侧向导排能力,减少滞水现象的出现；UDL层厚度只影响早期降雨时的侧向导排长度,但对持续大量降雨时的最终导排长度影响不大；覆盖层坡度越陡则越容易疏干边坡上部特别是UDL层中的水分。最后为在土质覆盖层设计中科学合理利用倾斜毛细阻滞覆盖层的侧向排水效应提出了优化建议。(5)采用基于非等温多孔介质中水热耦合运移控制方程的数值软件,考虑外界气候条件、地表土体蒸发、植被蒸腾对根系生长区水分的提取作用,建立土质覆盖层-植被-大气相互作用数值模型,针对我国湿润、半湿润和半干旱地区典型城市长期实测气象条件,系统分析了不同结构型式土质覆盖层的响应,最后针对我国不同气候区终场土质覆盖层的设计提出了建议。更多还原

【Abstract】 The principal goal of landfill final cover is to prevent or control infiltration of precipitation, thereby reducing leachate production, and to control the emission of landfill gas into the atmosphere. The alternative earthen final covers (AEFCs) are constructed with relatively non-plastic soils with greater durability and lower cost and it requires relatively lower post-closure maintenance than conventional covers, so AEFCs are good choices for the landfill final closure. At present, many landfills in China are close to its service life, so they need a final cover. Therefore, it is of practical significance to study the performance of AEFCs.The research works in this paper are based on the general project "Study on the water transport between landfill earthen final cover and atmosphere and its controlling method in humid areas" funded by National Science Foundation of China. Numerical simulations, model tests and analytical methods were carried out to study the issues. The main research works and conclusions are as follow.(1) The influence of rainfall patterns on the infiltration into landfill earthen final cover was investigated based on the infiltration-runoff boundary conditions proposed by Gitirana (2005). The results show that as the peak rainfall intensity occurs earlier, the cumulative infiltration will be larger for the non-uniform pattern under the same daily precipitation; the cumulative infiltration of advanced pattern (A1) will be larger than the uniform pattern under certain conditions; the cumulative infiltration of rainstorms will be less than the rainfall pattern with 24 hours duration; not only the uniform pattern but also the advanced pattern (A1) should be taken into account in the study of long term performance of AEFCs in humid areas.(2) An analytical solution for water movement in an infinite slope was presented on the basis of the governing equation for unsaturated flow. To obtain the analytical solution, it is assumed that both the soil-water characteristic curve and permeability function can be described with exponential functions. The analytical results were compared with the results obtained from the numerical simulation, which shows that the analytical solution is reasonable. The influence of soil properties and antecedent rainfall and subsequent rainfall intensity on the water movement and storage were investigated. The results show that the less the saturated permeability, the shallower the wetting front; the lager the desaturation coefficient, the shallower the wetting front; the larger the water storage capacity (θs-θr), the shallower the wetting front; for the capillary barrier, the volumetric water content and matric suction in the fine-grained layer changes greatly, but the volumetric water content profile in the lower layer almost remains at the initial value.(3) The model test system comprised of model tank, rainfall simulator, water collection and measurement system and monitoring system was developed. The water transport between capillary barrier and atmosphere and the performance of capillary barrier with unsaturated drainage layers under high rainfall intensity were investigated through the model test. The results show that runoff occupies 69%～77% of the total precipitation. The UDL can drain the water from AEFCs through lateral diversion. The lower the saturated permeability of surface layer, the lateral diversion will be more dominant than the deep percolation.(4) Numerical models combined the landfill earthen final covers with wasted disposal were developed. The influence of rainfall intensity, the thickness of the UDL, the thickness and saturated permeability of surface layer, the inclination of the cover on the diversion length were investigated through numerical simulations. The results show that the UDL can increase the diversion length of the common capillary barrier and reduce the occurrence of perched water. The thickness of the UDL can influence the diversion length in the initial stage of rainfall, but it can not increase the final diversion length of AEFCs subjected to continuous high rainfall. The steeper the cover slope, the more water will be drained from the cover, especially in the UDL. Some suggestions on the utilization of lateral diversion capacity of inclined capillary barriers were proposed to optimize the cover design.(5) The numerical model that can describe the interactions between landfill earthen final cover-vegetation-atmosphere was developed. The model based on the non-isothermal flow equation considering the thermal moisture coupling takes the meteorological condition, the evaporation from the ground surface and the transpiration of the vegetation into account. The performance of AEFCs in humid, sub-humid, semi-arid areas in China was investigated. Some suggestions for the AEFCs design in China are given based on the numerical simulations.更多还原