填埋场斜坡上土工膜受力特性的离心模型试验研究

由于垃圾土沉降大,斜坡上土工膜易受到较大下拽力而破损,影响衬垫系统防渗功能。通过离心模型试验对填埋场斜坡上土工膜在垃圾土重力和沉降作用下的拉力和应变进行了研究,并通过FLAC数值对比分析,可获得如下结论：试验采用的模型垃圾土能很好地模拟现场垃圾土,模型土最大沉降量可达土层厚度的20%;土工膜存在中性点,以中性点为界土工膜可分为受拉区和受压区,中性点的位置与坡度和沉降有关,从坡顶到中性点拉应变逐渐变小,从中性点到坡脚压应变先增大后减小;坡度和沉降是影响土工膜拉力发展的重要因素,坡度或沉降越大,拉力越大,沉降是通过改变界面强度的发挥程度来影响土工膜拉力的发展;当采用单糙面土工膜（上光下糙）时,外部作用力很难向土工膜下界面传递,土工膜锚固端拉力几乎为零。     

山谷型垃圾填埋场失稳模式离心模型试验研究

利用能够在超重力离心环境下旋转的模型箱,进行了山谷型垃圾填埋场离心模型试验。试验结果表明,在40g离心加速度的条件下,前坡40°,后坡45°的填埋场在坡肩处变形较大,沿底部界面失稳的可能性较小。当模型箱转动11.6°(对应填埋体前坡51.6°,后坡56.6°,底坡11.6°),填埋体开始出现整体滑移,随着模型箱的转动角度不断增大,整体滑移呈加速趋势,并伴随有填埋体本身的大变形,其中垂直坡底方向的变形大于平行坡底方向。当模型箱旋转26°后(对应填埋体前坡66°,后坡71°,底坡26°),破坏模式由整体滑移变为沿填埋体内部滑移破坏。试验再现了垃圾堆体沿衬垫界面失稳过程,为山谷型填埋场衬垫界面参数取值方法提供数据支撑。基于测量数据、分析了垃圾土变形、破坏发展规律,探讨了垃圾土抗剪强度参数取值的主要影响因素。     

基础局部沉降下土工格栅加筋衬垫系统变形特性的试验研究

基础局部沉降会引起垃圾填埋场衬垫系统中的土工膜产生较大的拉应变,有可能导致衬垫系统性能下降,因此正确评价衬垫系统的应变就显得非常重要。通过模拟试验,采用应变片和位移计对基础发生局部沉降后土工格栅加筋衬垫系统的变形进行试验研究。试验结果表明:环境温度对衬垫系统的变形影响较大;相同组成材料下土工格栅和土工膜叠放在一起比其他方案更能降低土工膜的应变;衬垫系统刚度对沉陷范围影响不大,但对最大应变值影响较大。所得结果对垃圾填埋场衬垫系统的设计具有一定的指导意义。     

应变硬化垃圾堆体抗局部沉陷研究

通过三种不同材料堆体的局部沉陷模型试验发现局部沉陷条件下应变硬化材料可能产生"自支撑"现象。利用模型试验和退化情况下的解析解验证了数值分析模型模拟应变硬化材料堆体局部沉陷问题的有效性。在此基础上比较了采用不同垃圾应力应变模型的分析结果,考虑堆体材料应变硬化的复合指数模型和线弹性模型计算得到的沉陷区土压力明显小于与之对应的摩尔-库伦模型计算结果,采用传统摩尔-库伦模型计算得到的沉陷区衬垫系统挠曲变形和应变值偏大,因而针对砂土材料的Giroud(1990)Trapdoor土拱效应理论应用于垃圾堆体局部沉陷分析时存在一定的局限性。进一步分析了各种参数对衬垫系统表面土压力和变形的影响,发现沉陷区衬垫系统最大挠度和最大应变随垃圾堆体高度的增加而增加,随垃圾堆体模量和加筋体刚度的增加而减小。最后提出应变硬化垃圾堆体在局部沉陷条件下衬垫系统土工膜的应变计算和加筋层的设计方法,对于垃圾填埋场衬垫系统抗局部沉陷设计具有一定的指导意义。     

垃圾填埋场土工合成材料的界面特性试验方法研究

拉拔、直剪、单剪试验常用于材料间界面特性研究,通过对垃圾填埋场中组成复合衬垫的土工膜、土工布和砂土、黏土界面分别进行了土工膜与砂土、土工膜与黏土、土工布与砂土、土工布与黏土的拉拔试验,土工布与砂土、土工膜与黏土的直剪试验及土工网–土工膜–黏土组合界面的单剪试验。研究结果表明:土工合成材料与土界面特性主要取决于土工合成材料的表面性质,直剪和单剪试验得到应力–位移曲线的初始斜率高于拉拔试验;法向应力由低向高变化时控制滑动面也发生了变化,界面特性受到防渗结构层中相邻材料的影响;在3种试验中拉拔试验得到的界面强度包线最高,单剪次之,直剪最低;单剪试验能较合理地模拟垃圾填埋场复合防渗结构的工作条件,建议利用单剪试验技术确定界面的强度参数,直剪试验也是可选择的试验方法。     

浅析HDPE防渗膜在填埋场的施工应用

通过HDPE防渗膜在生活垃圾填埋场中的应用,介绍了HDPE土工膜的施工工艺流程,HDPE膜的铺设安装要求及HDPE特殊部位的处理方法,探讨了HDPE土工膜的焊接程序及要求,以推广HDPE防渗膜的应用。     

考虑垃圾体成层性的渗滤液回灌运移规律

渗滤液回灌不仅能处理渗滤液、节约费用和保护环境,而且加速了填埋场稳定化,增加了产气率。以上海某填埋场四期工程为计算模型,本文考虑垃圾土沉降导致的成层性,运用SEEP/W有限元软件模拟渗滤液喷洒回灌。垃圾土在自重作用下会产生较大的沉降变形,导致垃圾土的孔隙率随深度变化,残余含水量、饱和含水量及饱和渗透系数也随之变化。在数值模拟中,以VGM(van-Genuchten-Mualem)函数描述垃圾土渗透系数与基质吸力关系,以流量边界模拟填埋场顶部、底部的渗滤液回灌和导排,分析了回灌过程中渗滤液的饱和-非饱和渗流情况,进而探讨了垃圾土成层性、回灌强度和排水流量对渗滤液运移规律的影响。     

潮州生活垃圾填埋场防渗膜的选材与施工

介绍潮州市锡岗生活垃圾卫生填埋场防渗膜(HDPE土工膜)的选用、铺设、焊接和检测,以及施工技术要点和质量控制措施。     

复杂荷载作用下填埋场HDPE土工膜受拉计算

采用FLAC程序对典型荷载作用下城市垃圾填埋场HDPE土工膜的受力状况进行了计算分析。3种荷载条件包括:36 m高垃圾堆体自重荷载(分层填埋);下卧软弱黏土层不均匀沉降引起的荷载;地震引起的动力荷载。计算结果显示:①土工膜内的拉应力随着垃圾土分层填埋、基础不均匀沉降、地震荷载的作用而积累;②基础不均匀沉陷是影响衬垫层土工膜局部拉应力的主要因素;③中等强度水平的地震动输入(例如,峰值加速度为0.25g)可使覆盖层土工膜端部锚固位置拉应力超过极限拉应力。     

大型垃圾填埋场垃圾挡坝拓建三维有限元数值模拟研究

以广州某垃圾填埋场为实际工程案例,利用有限元模拟软件Midas-GTS建立模型,对垃圾填埋场挡坝拓建过程中新旧坝体的垫层连接问题和土工加筋的加筋间距问题进行稳定性分析,同时,将数值模拟结果和现场监测结果对比。研究结果发现：挡坝在拓建时可以使用高强度的垫层减小挡坝的位移,防止新旧坝体间的位移;土工加筋后的坝体位移和塑性应变随着加筋间距的减小而减小;有限元模拟与现场监测数据由于垃圾堆体的存在有较小的差异,变形规律一致。研究分析结果可以为垃圾填埋场挡坝拓建和类似拓建工程提供应用参考和理论指导。     

Subsidence performance of landfills

This paper presents field measurements of landfill subsidence for five municipal solid waste landfills. Data from the.five sites are within the range of landfill subsidence reported in other publications.

At one site with variable subsidence of up to 10 percent of the landfill height in 3 years after capping, portions of an in-situ HDPE cap geomembrane were uncovered. The geomembrane showed no visual signs of subsidence-induced distress.     

Tension in geomembranes on landfill slopes under static and earthquake loading—Centrifuge study

Geomembranes are some of the most commonly used geosynthetics in landfill liner systems. Geomembranes may experience harsh environmental conditions such as extreme temperatures or earthquake loading. Earthquake loading can be an extreme loading case for landfills located in seismic regions. This study, based on dynamic centrifuge testing, investigates the effects of simulated earthquake loading on the tension experienced by the geomembrane on a landfill slope. The landfill modelled in the dynamic centrifuge tests was a 7 m high municipal solid waste (MSW) landfill with a single geomembrane-clay liner system (45° side slope and 10 m slope length). Results show that moderate earthquake loading (base acceleration between 0.1 and 0.3 g) can result in a permanent increase in geomembrane tension of 5–25%.     

HDPE土工膜端部张拉力的大规模实测数据分析

 垃圾填埋场边土工膜主要受到温度应力和垃圾压缩引起的张拉力的作用，为评价垃圾填埋场防渗系统中高密度聚乙烯(HDPE)土工膜的温度应力和垃圾填埋压缩引起的端部张拉力，以短纤维无纺布、HDPE土工膜组成防渗系统，进行大规模现场试验。试验结果表明：伴随环境温度的下降，HDPE土工膜中产生温度应力，当填埋高度较小时作用在HDPE土工膜端部的张拉力主要为温度应力；随着填埋高度的增加，压缩引起的HDPE土工膜端部张拉力增大。用有限元算法对压缩引起的端部张拉力进行分析，并采用温度与HDPE土工膜张拉力的关系对温度应力进行分析。计算结果与实测结果的对比情况表明，考虑填埋压缩引起的张拉力的应力松弛后计算结果更加接近实测结果。     

Shear strength of landfill liner interface in the case of varying normal stress

Landfills are sequentially filled by solid waste lifts, thus normal stress on the liner interface changes in different shear stages, which may affect selection of interface strength in landfill slope stability analysis. Shear tests were conducted at the liner interfaces of geomembrane/geotextile (GM/GT) and geomembrane/geocomposite/sand (GM/GC/Sand), and the normal stress changed in different shear stages. Values of friction angles on both the GM/GT and GM/GC/Sand interfaces obtained by direct and simple shear tests under increasing normal stress in the hardening, softening, and large-displacement stages were lower than those obtained by the traditional direct shear test. The reduction was greater for peak friction angles. Since the peak liner interface strength obtained by staged loading is lower than the peak interface strength by using the traditional shear test method, using the peak shear strength obtained from the traditional direct shear test for the base floor liner to conduct slope stability analysis may cause an un-conservative result. It is necessary to consider the effects of normal stress changes on the liner interface strength in landfill slope stability analysis.     

Assessment of HDPE geomembrane performance in a municipal waste landfill double liner system after eight years of service

In the late 1970s and early 1980s, environmental regulations were upgraded in a general national movement to effect secure management of our municipal and residual solid wastes. The new regulations required varying combinations of natural and/or synthetic barrier and drainage layers to prevent the unrestricted release of contaminants.

The acceptable barrier materials included synthetic flexible membrane liners (FMLs) of various types. One of those most commonly used has been high-density polyethylene (HDPE) geomembrane. HDPE has been selected because of its good chemical resistance characteristics, among others. Background compatibility testing has shown the HDPE geomembrane to be extremely resistant to the leachates that are generated by municipal and residual solid waste landfills. The background testing for design has generally been based on relatively short-term tests that are conducted under extreme conditions to ‘forecast’ service life.

Recently, a municipal solid waste landfill double liner system that was constructed in 1988 was exhumed. The HDPE geomembranes of this liner system had been exposed to varying degrees of leachate since 1989. Samples of the HDPE were extracted from the in-place liner system and were laboratory-tested for physical, mechanical and endurance properties. The selected suite of tests duplicated the test protocol conducted in 1988 as part of the liner system construction quality assurance (CQA) program.

The results of this testing show that the HDPE properties are still within the range of data generated by the original testing in 1988. No degradation in properties was indicated by this testing program. The HDPE had been exposed to the leachate, methane, and static and dynamic stresses for approximately 8 years. The results of this test program support the design selection of HDPE as the synthetic barrier component of this landfill liner system.     

垃圾填埋场沉降变形条件下气-水-固耦合动力学模型研究

基于多孔介质流气–水–固耦合和微生物降解理论,建立描述这一复杂动力学行为的二维气–水–固耦合数学模型,并给出耦合模型的数值格式。通过数值仿真实现垃圾填埋体的变形沉降及气体产生和迁移演化过程的可视化,得到气体压力及产气量随填埋年份的变化规律。数值计算结果表明:填埋体内总应力及孔隙度的改变与垃圾降解变化规律一致;抽气过程使场内气体压力得到释放;由于沉降作用填埋场内水相饱和度有增大的趋势,其中底部变化较顶部明显;此外,气井产量的变化与气体迁移单相模型的计算结果基本吻合,验证耦合模型的可靠性,其研究成果为垃圾填埋场沉降控制与气体资源化利用提供技术支持和理论依据。     

垃圾填埋场边坡上土工膜的受力分析

在垃圾填埋场中,土工膜可以隔离垃圾体与周围环境,避免地下水受到污染。在土工膜上填埋垃圾和土层,沿其长度方向将有剪应力作用,使得土工膜发生变形,内部产生拉力,为保证土工膜的安全使用,需要对土工膜的拉力进行分析。将土工膜与黏土界面的剪应力–位移关系曲线分为弹性、软化和残余强度3阶段,采用三阶段弹塑性模型来描述土工膜与黏土界面的剪切变形特性,推导出了界面处于弹性、软化和残余强度3阶段时土工膜位移–拉力的微分控制方程,由于3个阶段分界点的位置是未知的,利用迭代法求解土工膜的拉力,分析了填埋高度和坡度的变化对土工膜拉力的影响。     

土工膜破坏原因分析及防治措施

为了防止雨水流入垃圾中形成的渗滤液等多种有害物质流入地下污染地下水以及周围环境,现代垃圾填埋场都设置了防渗系统.防渗系统一般由无纺布、防渗材料以及膨润土土工毯等组成,由于在热应力、拉应力以及穿刺等各种因素的作用下,可能导致防渗系统破坏而使有害物质流入地下.介绍了造成防渗系统破坏的原因及其防治措施.     

Numerical study of strain development in high-density polyethylene geomembrane liner system in landfills using a new constitutive model for municipal solid waste

Tensile strain development in high-density polyethylene (HDPE) geomembrane (GMB) liner systems in landfills was numerically investigated. A new constitutive model for municipal solid waste (MSW) that incorporates both mechanical creep and biodegradation was employed in the analyses. The MSW constitutive model is a Cam-Clay type of plasticity model and was implemented in the finite difference computer program FLAC?. The influence of the friction angle of the liner system interfaces, the biodegradation of MSW, and the MSW filling rate on tensile strains were investigated. Several design alternatives to reduce the maximum tensile strain under both short- and long-term waste settlement were evaluated. Results of the analyses indicate that landfill geometry, interface friction angles, and short- and long-term waste settlement are key factors in the development of tensile strains. The results show that long-term waste settlement can induce additional tensile strains after waste placement is complete. Using a HDPE GMB with a friction angle on its upper interface that is lower than the friction angle on the underlying interface, increasing the number of benches, and reducing the slope inclination are shown to mitigate the maximum tensile strain caused by waste placement and waste settlement.