摘要
随着经济高速发展,环境问题日益突出,现代卫生填埋场是目前处置生活垃圾的有效、安全和最终的方法,其稳定性是关系填埋场安全和经济的重要问题。本文全面介绍填埋场的构造、类型、失稳模式及原因、稳定性主要影响因素和分析方法;重点研究设垃圾坝填埋场沿衬垫系统的折线平移破坏,以及沿填埋体内部圆弧旋转与沿衬垫平移的组合破坏,建立分析模型,探讨填埋场稳定性的变化规律;详细分析垃圾坝和渗沥液对填埋场稳定性的影响。
针对设垃圾坝填埋场,建立填埋场稳定性分析的平移破坏统一模型以及旋转和平移组合破坏模型。这二个模型都是将滑移体分为主动、中间和被动三个楔体,通过对各个楔体的极限平衡分析,建立方程计算填埋场稳定安全系数。
统一模型用于分析沿填埋场侧壁、底部及垃圾坝背部和沿填埋场侧壁、底部及垃圾坝底部的两种平移破坏模式的稳定。为验证模型的合理性,分析安全系数平均值和真实值的最大相对误差以及楔体间安全系数和整体安全系数的关系,并通过与未设垃圾坝的和设垃圾坝但只考虑单一破坏模式的分析模型的计算结果的比较,说明统一模型的正确性、可行性与兼容性。该模型能考虑垃圾坝断面形状、垃圾坝背与垃圾体作用力方向、复合衬垫系统界面的粘聚力和摩擦角等因素对平移破坏的影响,还能用于不设垃圾坝填埋场的平移破坏分析。根据二种破坏模式的分析结果,还可对垃圾坝断面进行优化设计。填埋场渗沥液对稳定性影响极大,液面增高,安全系数显著减小。通过对设垃圾坝填埋场四种渗沥液分布情况下的稳定分析,得出当底部渗沥液面水平,侧壁渗沥液面平行于侧壁时,填埋场稳定性最差的结论。
组合模型用于分析沿填埋体内部圆弧旋转与沿衬垫平移的组合破坏模式的稳定。通过最小安全系数的计算,确定组合破坏面位置。对于圆弧状的主动楔体,采用传统条分法。该模型能分析设垃圾坝填埋场可能发生的沿坝背或坝底滑移的组合破坏,也能分析不设垃圾坝填埋场的组合破坏。通过分析组合破坏安全系数的平均值和真实值的最大相对误差以及楔体间的和整体的安全系数的关系,并通过与单一的圆弧或平移破坏模式的计算值的比较,说明该模型的正确性和实用性。
最后,基于本文建立的设垃圾坝填埋场的统一模型和组合模型,以杭州天子岭第二填埋场(设垃圾坝)和厦门东孚填埋场(不设垃圾坝)为例,进行不同工况的稳定分析。
With the rapid economic development, environmental issues have become increasingly prominent, sanitary landfill becomes an effective, safe economic, and final way to deal with Municipal Solid Waste. Its stability is an important problem about economic and safety. This paper starts with aspects of landfill such as basic structure, type, failure mode, failure causes, main factors of failure, stability analysis methods. And then, it focus on the stability rules of the broken line translational failure of sanitary landfills with retaining wall along the interfaces of liner system and the combination failure of internal rotational failure in the landfill body as well as translational failure along the interfaces of liner system though building the analysis models. Moreover, influences retaining wall and leachate on the stability of sanitary landfill are analyzed in detail.
Consistent model and combination model are built for analysis the stability of sanitary landfills with retaining wall, which is divided the failure body into active, middle and passive wedges. An equation is established to calculate the safety factor through the limit equilibrium analysis of every wedge.
The consistent model is developed to analysis the translational failure of sanitary landfills with retaining wall along the lateral phase and the base of landfill as well as the back or base of retaining wall. To verify the model is reasonable, the maximum relative differences between average and true factors of safety are calculated and the relationship between the safety factors of wedges and whole fills are analyzed. The factors of safety are also compared with the results by the model of two wedges for landfills without retaining wall and the model of one failure style only for landfills with retaining wall. Those show that the consistent model is corrective, suitable and comprehensive. The model can consider the influence of the section of retaining wall, the force direction between the back of wall and the waste fill as well as the cohesion and friction angle along the interfaces of combined liner system. The model can also be used to analysis the translational failure of landfills without retaining wall. The optimum design of retaining wall can be conducted according to the results of the consistent model. Leachate is a tremendous impact on landfill stability. When the leachate level is increasing, the safety factor is reducing significantly. Further, through the analysis of four conditions of leachate distribution in landfills with retaining wall, Each safety factor of leachate distribution is calculated separately, then the conclusion which landfill stability is worst when the leachate level is horizontal to the foundation and parallel to the sidewall.
As for the combination failure of internal rotational failure in the landfill body as well as translational failure along the interfaces of liner system in landfills, the combination model is developed. Through calculating the least safety factor, the least safety factor is searched. The slice method is used to analyze the arc- shaped active wedge. The model can not only be used to analyze the combination failure in landfills along the back or base of retaining wall, but also to analyze the combination failure in landfills without retaining wall. It shows that the analysis model of combination failure is corrective and practical, which the maximum relative differences between average and true factors of safety are calculated as well as the relationship between the safety factors of wedges and whole fills are analyzed, more then, the safety factors of combination failure are also compared with that by the model of rotational or translational failure.
Finally, based on the stability analysis models of translational failure and combination failure in sanitary landfill in this paper, the stability of the second sanitary landfill in Hangzhou Tianziling(with retaining wall) and the sanitary landfill in Xiamen Dongfu(without retaining wall) are analyzed in different conditions.
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