【作者】 谢海建；

【导师】 陈云敏；

【作者基本信息】 浙江大学 ， 岩土工程， 2008， 博士

【摘要】 垃圾填埋场产生的高浓度和高毒性的渗滤液对填埋场底部和周边水体和土体造成了很大的威胁。国内外许多研究表明即使填埋场建造了标准的防渗系统,仍有相当多的场地对地下水和周围土体造成了污染。本文对国内外填埋场渗滤液的组分及其稳定化问题进行了总结和分析,得到了适合设计的渗滤液稳定化时间,并在此基础上提出了填埋场衬垫系统的击穿时间应大于渗滤液稳定化时间和填埋场运行期之和的设计理念;同时对国内外文献报道的渗滤液主要污染物在土、土工膜(GM)和土工复合膨润土垫(GCL)中的环境土工参数进行了汇总和统计分析,给出了这些参数的设计取值范围。对污染物在成层介质中的一维扩散(包括层状土和复合衬垫)机理进行了研究;提出了简化的分段式吸附等温线,并在此基础上研究了能考虑非线性吸附的污染物扩散模型。基于等效边界研究了污染物在复合衬垫中的一维渗漏-扩散问题。借助于这些理论分析方法研究了污染物在成层介质中的运移特性,研究了复合衬垫防污性能的影响因素,比较分析了我国常用的几种衬垫系统之间的防污性能等效性,并针对不同工况研究了GCL和压实粘土衬垫(CCL)的等效性。最后针对七子山填埋场进行了渗滤液运移的现场试验研究。取得了相应的研究成果:(1)得到了污染物在层状土和复合衬垫中的一维扩散解析解,并提出了层状土的平均扩散度。该解能考虑任意有限厚度介质层的扩散问题,同时能考虑初始浓度分布的影响及污染源浓度变化的影响。(2)结合分段式吸附等温线,得到了污染物在土体中的一维扩散解析解。该解析解具有简单和方便的特点,能较好地考虑土体对污染物的吸附作用。(3)基于等效边界的理念,得到了污染物在复合衬垫中的一维渗漏-扩散解析解,并在此基础上给出的无量纲设计曲线能有效地应用于基于性能的填埋场复合衬垫系统的初步设计。(4) 2m CCL和GM+CCL具有良好的防污性能。对于重金属离子,仅考虑其通过复合衬垫的渗漏作用会得到不确切的计算结果,复合衬垫下方的CCL和GCL的扩散性能和吸附性能对其的影响相当大。低水头作用时GM+GCL对于重金属离子的防污性能较好,随着水头的增大GM+GCL的性能显著下降。对于挥发性有机污染物,GM+GCL防污性能最差。(5)作为单一衬垫和作为复合衬垫两种不同情形下GCL等效于CCL的厚度均不超过0.1m。分析表明对于重金属,为达到与标准的GM+CCL同样的防污效果,需要在GCL下方增加的土壤保护层(AL)的厚度为5m。对于挥发性有机污染物,为达到GM+CCL同样防污性能则需要GM/GCL/AL系统中AL的厚度约为2 m。实际工程CCL取料困难及施工难度大时,可采用GCL+5 m AL代替。(6)考虑到挥发性有机污染物能通过扩散作用较快地通过GM,建议对填埋场的挥发性有机污染物含量进行控制。分析表明提高AL层对挥发性有机污染物的吸附能力能有效减少该层的厚度。GM+GCL+有机改良AL系统值得采用和推广。(7)现场试验表明13年后,Cl~-在填埋场底土中的运移深度超过了10 m。将一维扩散理论与实测结果的比较知对流作用对于污染物的运移较为重要;将一维对流-弥散解析解与实测数据的比较则可得到粘土层相关运移参数的取值范围,可为污染物进一步运移提供依据。(8)必须对填埋场的水头进行控制,如采用合适的填埋场封顶系统及渗滤液导排系统使得填埋场的水头能控制在一个较低的范围(如小于1m)。另外,土工膜和压实粘土的施工质量应进行严格的控制。更多还原

【Abstract】 The high concentration and high toxicity leachate generated in landfills have become a great threat to the surrounding environment. Though the standard liner systems have been constructed for many landfills to impede leachate contaminants, the groundwater and surrounding soils do have been contaminated due to landfilling.The components and the stabilization issues of the landfill leachate from China and the foreign countries were summarized and analyzed in the present paper. The time required for the leachate to be stable was suggested for liner design. The landfill liner system should be designed in such a way that the breakthrough time of the liner systems must be larger than the leachate stabilization time plus the landfill operation time. The transport parameters for different contaminants in soils, geomembranes (GM) and geosynthetic clay liner (GCL) were summarized and the typical values for design purpose were suggested. The mechanism of contaminant diffusion through layered media was studied by models. On the basis of a presented simplified non-linear adsorption isotherm, the effect of nonlinear adsorption on contaminant diffusion through soils was also investigated. Furthermore, the leakage and diffusion transport of contaminant transport through composite liners was investigated on the basis of the concept of equivalent boundary. Using the analytical and numerical methods presented, the performance of landfill liner system was studied and the equivalency between different liner systems was also evaluated. Finally, a field investigation on contaminant transport in landfill basal soil was carried out. The main conclusion is as follows:(1) An efficient general analytical solution and an elegant computer program have been developed for the problem on one dimensional contaminant diffusion in a layered media. The average degree of diffusion of the layered system is introduced based on the analytical solution. The model accounts for the arbitrary initial conditions and the variation of contaminant in the source.(2) An analytical solution of solute diffusion through soil is presented based on a simplified non-linear adsorption isotherm. The adsorption of solute on the clay minerals can be well reflected by the present isotherm. The presented method is relatively simple to apply and can be used for evaluating experimental results, and verifying more complex numerical models.(3) An analytical solution has been obtained for the leakage and diffusion transport of contaminant through composite liner on the basis of equivalent boundary. Non-dimensional design curves were developed for preliminary performance-based design of landfill composite liners.(4) 2m CCL and GM+CCL can provide better barriers for landfill leachate. As for heavy metal ions, leakage through composite liners is not the only important mechanism of solute transport in composite liners. The diffusion coefficient and the adsorption capacity of the underlying CCL or GCL have great influences on solute transport through composite liners. GM+GCL is a good barrier for heavy metal ions in the case of low leachate level. However, the breakthrough time of GM+GCL decreased greatly when the leachate level increases. Furthermore, GM+GCL is the worst liner systems for volatile organic contaminants.(5) It is indicated that GCL is equivalent to less than 0.1m of CCL in terms of both single liner and as a part of composite liner. For media having hydraulic conductivity, diffusion coefficients, distribution coefficients, and porosity similar to those considered in this study, the additional thickness of attenuation layer (AL) underlying GCL should be about 5.0 m for equivalency with GM+CCL standard composite liner for the heavy metal ions. The additional thickness of AL should be about 2.0 m for equivalency with GM+CCL standard composite liner for volatile organic contaminants. CCL can be substituted by GCL+5 m AL when the construction quality of CCL cannot be assured.(6) The concentration of volatile organic contaminants in the leachate should be controlled since they can readily diffuse through GMs. Furthermore, it is indicated that the thickness of the AL needed to achieve the same breakthrough time as the standard liner systems can be greatly reduced when the adsorption capacity of AL can be improved. The composite liner consisting of GM, GCL and the organo-treated AL or organo-treated CCL should be adopted and popularized.(7) The filed investigation indicate the maximum depth of migration of chloride was beyond the depths at each of the boreholes, while the migration distance of COD varied between 1 m-3.5 m for the four boreholes for 13 years of landfill operation period. It is indicated that advection transport maybe the dominant mechanism rather than diffusion transport. The range of the transport parameters of the contaminant were obtained by comparing the field data with the theory of one-dimensional contaminant transport.(8) Retro-fitted measures should be taken to control the leachate level and control the leachate generation rate. Furthermore, the construction quality of geomembrane and the compacted clay liner should also be controlled.更多还原