Controlling strain in geosynthetic liner systems used in vertically expanded landfills

According to relevant new regulations in China,a composite liner system involving geosynthetic materials must be installed at the bottom of an expanded landfill.The deformation and integrity of the composite liner under a variety of factors are important issue to be considered in the design of a landfill expansion.In this paper,we investigate the strain distribution in geosynthetic materials within the composite liner system of expanded landfills,including strains in geosynthetic materials resulting from overall settlement and lateral movement of landfills,localized subsidence in landfills,and differential settlement around gas venting wells.The allowable strains of geosynthetic materials are discussed based on the results of tensile tests,and the corresponding design criteria for composite liner systems are proposed.Meanwhile,practical measures allowing strain control in geosynthetic materials used in landfill engineering are proposed.     

Seismic displacements of landfills and deformation of geosynthetics due to base sliding

Seismic design of waste landfills has been a subject of intense research over the past two decades, primarily due to the severe environmental impact of a potential failure. The majority of the related studies have been focused on the stability assessment of landfills utilizing permanent deformation methods. However, previous investigations have not fully addressed the impact of the composite liner system on the seismic performance of the geostructure, mainly expressed as potential sliding development, which is greatly affected by the geometry and the resulting initial static stress state of the landfill. Therefore, the aforementioned issues are investigated via a detailed parametric study, where the dynamic behaviour of the composite liner system is examined both analytically and numerically. The conducted coupled analyses indicated that the most significant parameters of the complex dynamic response of waste landfills can be reduced in two ratios that comprise functions of the main characteristics of the geostructure and of the excitation. Moreover, two distinct failure patterns have been identified with respect to the characteristics of the distribution of the permanent displacements along the interface and the axial deformation along the geosynthetic. The occurrence conditions of these failure patterns can be determined in terms of the two abovementioned ratios as verified by the analytical results of the critical acceleration of a simple SDOF system.     

城市垃圾填埋场堆体地形的改造设计 策略研究

随着中国城市土地资源的优化配置与存量利用成为趋势,城市垃圾填埋场越来越多地被改造为公园绿地、游乐场等公共活动用地,其中垃圾填埋堆体地形改造是垃圾填埋场改造中的难点和重点。垃圾填埋堆体的景观改造与一般景观地形建设相比,技术复杂性更高,设计限制条件更多。首先综述了堆体类型与景观改造目标,从堆体地形的特点、稳定性、填埋场区位与堆体形态及布局的关系等方面探讨了垃圾填埋堆体景观改造的技术要点,并结合优秀案例对不同类型堆体的景观改造策略进行深入分析与归纳,旨在为垃圾填埋场堆体景观改造实践提供相应技术与方法策略指引。     

卫生填埋场的平移破坏及影响因素

卫生填埋场的稳定性是填埋场设计、施工、运营和封场后最主要的考虑因素之一。本文介绍了卫生填埋场的基本构造、主要失稳模式和平移破坏研究现状,提出填埋场垃圾坝优化设计概念,并对填埋场平移破坏主要影响因素的研究现状、试验方法和取值进行探讨。     

Geosynthetic liner integrity and stability analysis for a waste containment facility with a preferential slip plane within the liner system

The paper examines the effects of settlement-induced downdrag on geosynthetic liner systems for a waste containment facility with steep side slopes for different design scenarios, and conducts the stability analysis of the waste mass during waste filling operations. Without the presence of a reinforcing layer above a geomembrane (GMB) liner, the liner experiences unacceptable tensile strains under both short- and long-term downdrag waste settlements. It is shown that an anchored high strength/stiffness geotextile (HS-GTX) reinforcement over the GMB can reduce the GMB tensile strains to less than 3%, but the HS-GTX itself may be overloaded. A geosynthetic slip layer over the full or partial HS-GTX reinforcement overlying the GMB can reduce the tensile strains of the GMB to less than 3% and of the HS-GTX to less than 5% by providing a preferential slip plane between the geosynthetic slip layer and the HS-GTX. A rupture of the geosynthetic slip layer is likely to occur resulting in the exposure of the HS-GTX to the waste, but the protection of the GMB by the HS-GTX is still expected. The results from the stability analysis show that, during waste filling operations under a given factor of safety, there is a critical relationship between the width of the top of the waste pile and the total waste thickness.     

设垃圾坝填埋场的三楔体滑动分析

 提出新建及扩建设垃圾坝填埋场的三楔体极限平衡分析法，给出安全系数的近似解，使得填埋场沿背部、底部及垃圾坝内坡处衬垫界面的三折线型滑动分析大为简化，发现其具有较好的工程适用性。该方法与精度较高的Spencer法所给出的计算结果吻合良好，且能考虑填埋体内摩擦角的影响。研究结果显示，衬垫界面的强度直接影响填埋体沿衬垫界面的稳定性，而填埋场各坡坡度、填埋场高度和宽度以及垃圾坝的高度对安全系数均有较大的影响。对扩建填埋场的分析结果表明，扩建填埋体沿新老场交界面的安全系数较低，在扩建填埋场的设计中应引起重视。另外，扩建填埋场的横向扩建宽度越大，则其界面安全稳定性越好。     

CERCLA landfill closures: Construction considerations

A properly functioning cover over an uncontrolled landfill which is regulated under the Comprehensive Environmental Response Compensation and Liability Act (CERCLA) depends on both a well-engineered cover design and prudent construction practices.

This paper focuses on several geosynthetic construction issues which ultimately impact the performance of the final constructed cover. Preparation and placement issues related to subgrade preparation, geosynthetic placement, cover soil placement and test sections are presented. Storage and seaming of the geosynthetics are discussed. Construction quality control and quality assurance programs are emphasized. In addition, relevant design issues pertaining to settlements, interface friction, and rigid-nonrigid connections are discussed.

Although these issues apply to all landfills, this paper is based on experience gained from design, review and construction oversight of CERCLA landfill covers by the US Army Corps of Engineers.     

Design and placement considerations for clay and composite clay/geomembrane landfill final covers

The performance of clay and clay geosynthetic combinations for landfill barrier layers has not always proved predictable and the integration of geosynthetic materials into conventional landfill designs presents some interesting problems which were previously unforeseen.

This paper looks at identifying and mapping the approach to some specific considerations for clay and geomembrane/clay barriers. These considerations include: long-term performance of clay barriers, short-term and long-term stability of clay barriers, clay/geomembrane interface behavior, and the phenomena of moisture build-up beneath exposed membrane liners.     

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。     

Modelling the behaviour of mechanical biological treatment outputs in landfills using the GasSim model

The pretreatment of the biodegradable components of municipal solid waste (MSW) has been suggested as a method of reducing landfill gas emissions. Mechanical biological treatment (MBT) is the technology being developed to provide this reduction in biodegradability, either as an alternative to source segregated collection or for dealing with residual MSW which still contains high levels of biodegradable waste. The compost like outputs (CLOs) from MBT plants can be applied to land as a soil conditioner; treated to produce a solid recovered fuel (SRF) or landfilled. In this study the impact that landfilling of these CLOs will have on gaseous emissions is investigated. It is important that the gas production behaviour of landfilled waste is well understood, especially in European member states where the mitigation of gaseous emissions is a legal requirement. Results of an experiment carried out to characterise the biodegradable components of pretreated biowastes have been used with the GasSim model to predict the long term emissions behaviour of landfills accepting these wastes, in varying quantities. The landfill directive also enforces the mitigation of potential methane emissions from landfills, and the ability of landfill operators to capture gaseous emissions from low emitting landfills of the future is discussed, as well as new techniques that could be used for the mitigation of methane generation.     

Case histories of landfill erosion protection using geosynthetics

This paper presents case histories of geosynthetics installed for erosion control at solid waste landfills. A case history of a successful application at a landfill in Ohio is discussed, along with a less successful application at a landfill in Missouri. The erosion process and typical design standards employed at modern landfills to mitigate the effects of erosion are discussed. Discussion of an ongoing research project and recommendations conclude the paper.     

城市生活垃圾填埋场气压分布一维稳态分析模型

掌握填埋场气压分布是填埋气灾害控制和资源化利用的基础。提出了分层垃圾填埋体气压分布一维稳态分析模型及求解方法。该模型可分析含有给定抽气压力或给定抽气流量水平导气层的填埋体气压分布。采用该模型探讨了垃圾分层特征、封顶覆盖层下和填埋体内的高渗透性水平导气层、填埋体底部渗沥液导排系统兼作填埋气导排通道对填埋体气压分布的影响规律。通过参数分析得到以下结论：填埋体垃圾不考虑产气速率和固有渗透系数随垃圾埋深增加而减小（产气速率和固有渗透系数按埋深平均）会高估填埋体内气压;封顶覆盖层下和填埋体内设置水平导气层可有效降低填埋体内气压;填埋体底部填埋气导排通道对填埋气气压较大的深部垃圾降压效果较明显。分析结果表明,该模型可指导填埋气收集系统设计,如水平导气层位置和间距布置及抽气功率选择等。     

垃圾填埋场边坡稳定安全监测指标及警戒值

随着垃圾的产量和填埋量迅速增加,垃圾堆体的稳定问题日益突出,填埋场运行中安全监测显得十分重要。针对某大型垃圾填埋场失稳事件,对该填埋场堆体边坡开展了近2年的监测,获得了各种气象条件下渗滤液水位、地表水平位移、竖向位移、深层侧向变形等监测数据,特别是2008年6月强降雨期间垃圾堆体边坡局部失稳和2009年2月污泥坑周边堆体滑移过程中完整、全面的监测数据。基于监测数据,并结合实际降雨条件、填埋场运行状况,对填埋场失稳的内在因素进行详细的分析,得出渗滤液水位过高是导致堆体边坡失稳的主要内因,水平位移速率是填埋场边坡稳定状态最为敏感的指标。最后 根据监测数据 进行统计分析 ,提出垃圾填埋场稳定安全监测关键指标及警戒值, 为今后垃圾填埋场的现场监测工作提供重要依据 。     

Oberflächenabdichtungen aus PE‐HD‐Dichtungsbahnen für Altdeponien

Surface lining with HDPE geomembranes of old municipal waste landfills. Until mid‐2005 approximately 250 old municipal waste landfills have to be closed, because they failed to meet the requirements according to the state of landfill engineering. After closure, a containment and remediation concept has to be put into action. At landfill sites with appropriate conditions (e.g. base liner and waste water collection system), one may try to stabilize the waste body by forcing up through water infiltration the anaerobic biochemical reaction within the waste body or by aerobic stabilization techniques. However, engineered capping systems are an indispensable tool in the containment strategy for waste disposal. Reliable, highly effective and long lasting liner systems can be installed even under the special conditions on the surface of old landfills. In particular, selected HDPE geomembranes are highly suited for these conditions. However, approval of geomembrane products for this application is essential, since geomembranes made of different HDPE resins as well as differently produced out of the same HDPE resin may extremely differ in their long‐term and installation properties.     

Colloid and heavy metal transport at landfill sites in direct contact with groundwater

Colloids are ubiquitous in aquatic systems and are suspected of facilitating contaminant transport. At sites where the disposed waste is in direct contact with ground water, two main prerequisites for colloidal transport are fulfilled: these two prerequisites are a high concentration of colloids and many different contaminants, some that are very unlikely to be transported in an aqueous solution. In our investigation, three landfill sites with different historical background and hydrogeological conditions were examined. The colloids upstream, downstream, and inside the waste disposal sites were characterized with respect to their size distribution and chemical composition. The particle concentration upgradient and downgradient of the sites were 2-23 and 8-80 mg/L, respectively. Inside the waste disposal sites the particle concentration was 160-870 mg/L. The particles upgradient reflected the mineral composition of the aquifer, with calcareous colloids and silicates dominating the composition. Downgradient of the sites, we saw an increase of iron-precipitates and salt colloids, together with organic colloids. However, the downgradient colloids were significantly different from the colloids and particles inside of the disposal sites with respect to their size and chemical composition. Colloids inside the disposal sites reflected the waste composition and degradation. The association of heavy metal ions to colloids and particles showed a surprisingly high fraction of dissolved metal ions. We determined that the lowest metal ion concentrations (less than 20% of the total concentration) were associated with the colloid size class between 10 nm and 1 microm, which is considered most mobile in porous systems. The association of Fe and Mn to colloids was dominated by the redox conditions inside the disposal sites, where there was a reducing environment, Fe and Mn were dissolved. Outside the disposal sites, where there was an oxidizing environment, these metals formed colloids and particles >1 microm. Together with these particles, As was precipitating. For other metal ions (Cd, Co, Cu, Ni, Pb, Zn), we determined an association to colloids coinciding roughly with the colloid size distribution. The results suggest that the change of hydrochemical conditions at the interface, from a reducing, high ionic strength environment inside of the disposal sites to an oxidizing, low ionic strength environment in the groundwater together with physical filtration effects for the larger particles, is an effective chemical barrier for colloids. Field observations suggest, that the colloids form a rather persistent coating around the aquifer matrix that reduces the hydraulic conductivity and enhances the sorption capacity of the aquifer close to the waste disposal sites. In every case, there was an increase of the contaminant concentrations downstream of the waste disposal sites, but the increase was less than expected from the initial transport calculations, which were under the assumption that there was a direct contact between the waste disposal site and the groundwater. It seems more than likely, that under the given conditions, colloids are contributing to a self sealing layer at the landfill bottom. The results of this study are relevant for the assessment of many landfills without appropriate landfill sealing systems.     

Evaluation of Interface Shear Strength between Geosynthetics Under Wet Condition

This paper presents direct shear testing data for interfaces between a nonwoven geotextile or two types of geosynthetic clay liners (GCL) (reinforced and unreinforced) and two types of geomembranes (smooth and textured). In this study, the effect of moisture on interface shear behavior was investigated by performing shear tests in both dry and wet (or hydrated) conditions because the geosynthetic interfaces in a landfill are easily exposed to rain, leachate and groundwater beneath the liners. The degree of strength reduction with increasing displacement and the effect of the normal stress level on friction angles were examined, and the modified hydration method applied for the GCL was also validated. The test results showed that the normal stress level, interface water presence and hydration methods dominated the interface shear strength and behavior. The relationship between the peak secant friction angle and the normal stress demonstrated that the friction angle decreased with increasing normal stress, implying that the shear strength for safe design should be determined by using the maximum value of the normal stress applied in landfills. Finally, comparisons with a few published test results were presented and some design implications for the geosynthetic-installed landfills were discussed.     

城市固体废弃物(MSW)的工程性质

填埋是处理城市固体废弃物（ＭＳＷ）的主要方法，对现代卫生填埋场进行设计和审查时均需进行广泛的土工分析，正确选择废弃物的工程性质对填埋场设计工作极其重要。由于ＭＳＷ构成极不均匀，其工程性质变化范围很大，并随时间而变，而且很难进行直接量测。本文根据收集到的资料，给出了ＭＳＷ某些工程性质如容重、含水量、孔隙率、渗透性、持水率、凋蔫湿度、抗剪强度和压缩性等的典型值，可供现代卫生填埋场进行初步工程评价时作参考。     

三峡库区污水处理厂污泥处置现状研究

目前,重庆三峡库区共建有污水处理厂18座,日产污泥132．95t／d。污泥处理主要采用浓缩＋机械脱水的工艺,然后送至垃圾填埋场填埋。运行过程中,由于脱水污泥含水率较高（80％左右）,且未经稳定化处理,已经极大的影响了填埋场的正常运行。针对这种情况,本文提出：在有垃圾填埋场的情况下,通过机械脱水、石灰稳定化等处理后进行填埋,不具备卫生填埋条件的实行堆肥后资源化利用。     

垃圾填埋场渗沥液水位壅高及工程控制

 我国垃圾填埋场渗沥液水位普遍壅高,严重影响安全运行。测试和总结垃圾的持水特性、饱和渗透系数以及渗沥液导排层渗透和淤堵特性。通过数值分析,揭示垃圾初始含水率、持水特性以及垃圾和导排层渗透系数对填埋场水位的影响规律。结果表明,垃圾饱和渗透系数随深度和龄期减小、导排层淤堵、垃圾初始含水率高导致水位明显壅高;而垃圾饱和渗透系数较小时,堆体内易形成局部滞水。结合实际工程,验证数值模拟结果,提出并实施水位壅高控制的工程措施,效果十分显著。     

Interface friction: An owner''s perspective

The introduction of geosynthetics to landfill applications has generally resulted in significant environmental protection improvements. Most significant applications have been the use of geomembranes in landfill liners and final covers. Other geosynthetics that are commonly utilized, often in conjunction with and adjacent to geomembranes, include geotextiles and geonets. However, when geosynthetics are used, especially when they are placed adjacent to each other in a liner or final cover configuration, the frictional characteristics of the resulting interfaces can become a very important factor affecting the design, construction and operation of a landfill. The impact of the frictional characteristics of such interfaces and the related potential stability issues on the design, construction and operation of landfills, from a landfill owner's perspective, is the subject of this paper.