Geotextiles in landfill closures

There are numerous areas of geotextile application in landfill covers, each with a somewhat unique set of requirements and considerations for the proper selection and evaluation of the most appropriate material. This paper provides an overview of geotextile requirements and specific references to available design literature for each of these application areas.     

Geosynthetics in landfill closures design considerations

Geomembranes can provide an effective low permeability cover at many sites. Maintenance of overall stability is essential to design performance. The beneficial effects of textured geomembrane, drainage terraces and tensile geogrids are discussed. The use of both vegetative and non-vegetative covers to resist erosion is presented. The effects of construction equipment traffic, freezing, root growth and vermin on the geomembrane are also discussed. Finally, geomembrane penetrations and a closure concept which does not physically join the closure geomembrane to the bottom geomembrane are discussed.     

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.     

Optimal placement of reinforcement in piggyback landfill liners

The optimal placement of geogrid reinforcement in clay liners subject to differential settlement was investigated both numerically and with centrifuge modelling. Two unreinforced liners, a liner reinforced at the top-quarter depth, a liner reinforced at the bottom-quarter depth and a double reinforced liner were modelled in the centrifuge. Differential settlement was induced on the model liners by lowering a trapdoor overlain with sand. By considering: 1) the magnitude of differential settlement required to induce micro-cracks in the liners, 2) the strain fields across the liners during differential settlement and 3) the distribution of these strain fields, it was found that dividing the available reinforcement equally between the top-quarter and bottom-quarter of the liner, i.e. double reinforcement, represents the optimal reinforcement strategy.     

Addressing the special concerns of landfill closures: VLDPE and textured geomembranes

Landfill closures often require a somewhat different set of properties for synthetic liners than do landfill bottom liner installations. In particular, cap design usually presents the geotechnical engineer with greater concerns regarding long-term slope stability and accommodation of differential settlement. Friction between synthetic liners and materials contacting those liners, multiaxial elongation, and flexibility increase in importance. Since leachate does not contact the liners, chemical resistance becomes less important. Resistance to the components of landfill gas is, in most cases, all that is necessary.

As a result, synthetic liners with a textured surface to improve friction angles, and very low density polyethylene (VLDPE) geomembranes are becoming very attractive to geotechnical engineers. They provide considerable improvement in those areas which are important for cap installation. These materials, however, behave differently in standard index and performance testing of geomembranes, when compared with traditional polyethylene liners. These behaviors and differences are important for geotechnical engineers to understand. They are discussed in this paper.     

Geogrid connections

Connections can have a significant impact on the performance of geosynthetic systems whether their intended function is separation or reinforcement. When reinforcement is the function, the connection must be considered as a limiting strength factor and evaluated by the same performance standards as the reinforcement material alone. If used in critical structures with design lives of more than 1 or 2 years, the geosynthetic and its connections must be evaluated for durability limitations such as creep, site damage and chemical degradation. Geogrid connections typically fall into this category.

Geogrid connections are accomplished by either overlapping or mechanical connections. Overlap connections must be designed and constructed to assure proper overlap lengths. Overlap length is governed by soil interaction behavior. Geogrid-soil interaction is measured by pull-out testing and pull-out performance is a function of geogrid dimensional stability. Overlaps can be secured by a variety of tyiing techniques but these ties are not efficient for load transfer. Geogrid Bodkin Joints are the preferred mechanical connection for assuring full load transfer between adjacent layers of some geogrids.

This paper discusses geogrid connections, the techniques used, and the factors that affect their performance.     

经编和玻纤格栅加筋粘性土的三轴试验研究

对经编格栅和玻纤格栅加筋粘性土进行不固结不排水的三轴压缩试验。试验结果表明,在粘性土体上布置格栅筋材,都能提高土体强度,但不同的筋材,其加筋效果是不一样的,经编格栅加筋土的加筋效果要优于玻纤格栅加筋土。加筋层数越多,加筋效果越好;随着加筋土应力增加,加筋土抵抗变形的作用才能得到更充分发挥,土体加筋效果更明显。不同筋材的加筋土,其粘聚力与内摩擦角的变化规律不一致;玻纤格栅和经编格栅加筋粘性土的加筋效果与砂土不同,不仅表现在粘聚力的增加上,还表现在内摩擦角的增加上。加强筋条结点连接的牢固性,能够提高加筋效果。     

Project-ending competence in premature project closures

Project management literature tends to focus on the early phases of a project and on the associated generic project management competences, such as planning, scheduling, budgeting, resourcing and motivating. Only a small fraction of the discussion is devoted to project closure and to the competences needed when a project fails to reach the goals and so needs to be closed prematurely. The purpose of this paper is to develop an understanding of project-ending competences needed in premature project closures. Two cases of premature project closure are analysed in different contexts: in the car industry and the aircraft manufacturing industry. The key findings concern the managerial challenges that are present in premature project closures: the need for involvement of senior and also project managers, the need to understand the often changed role of internal and external project stakeholders, and the need to understand that the ‘future matters’ in premature project closure.     

土工格栅加筋边坡优化设计研究

基于加筋材料的拉拔试验结果和极限平衡理论,针对具体边坡工程进行了不同加筋方案的计算与分析,对比了计算模型和设计方法的适用性,给出了满足边坡稳定条件的最佳设计方案。计算结果表明:采用改进瑞典法或荷兰法的计算结果相近且较原瑞典法有明显的提高,更能体现加筋效果;地震效应和地下水对加筋结构有较大影响;水利法应用于稳定地基上加筋边坡目的性强,能获得满足稳定性条件的合理布筋量;当地下水位较高时,筋材宜通铺。双层加筋效果较单层加筋有明显提高,但并非后者的简单叠加。单层加筋时,铺设位置对于边坡稳定性的影响有限,若铺设于坡身更能减少布筋量,降低造价。对比分析还表明,无论采用何种加筋方式,加筋前后的最危险滑弧位置均会发生改变,后者会向边坡中心和地基深处发展,对于提高其稳定性有明显作用。     

土工格栅使用中的几个问题

通过产品技术性能的对比,提出当前国内设计使用土工格栅中存在的一些问题和发展我国土工格栅的对策。为了使土工格栅达到与国际接轨的目的,以英国耐特龙集团公司的产品标准作为一个相对的基准对国内产品进行了评价。强调了对使用周期长的工程,设计时必须选用格栅的蠕变强度,而不是质量控制强度。介绍了蠕变强度的一系列评价方法,提出了国产塑料土工格栅与世界接轨的建议。     

土工格栅在边坡加固工程中的应用实例

阐述了土工格栅加筋挡土墙作为一种新型的柔性支挡结构,具有工期快(短)、投资省、适应力强等优点,着重分析了其原理,并结合具体的边坡治理工程实例,对其设计方式及施工方法作了简单介绍,并与传统的边坡治理手段在经济上进行了分析与对比,其成果显示土工格栅加筋挡土墙节省投资近1/4。     

土工网在桥头引道路堤中的应用研究

以室内试验研究了路基土与土工网之间的综合摩阻力、张力膜效应及不同土工网铺设间距对复合土反应模量的影响，并依托上海市城市外环线1期工程，研究了桥头引道加筋路堤和不加筋路堤的地基顶面垂直土压力、水平土压力、地基顶面沉降、路堤坡脚侧向位移和路面工后沉降等．结果表明，将土工网加筋路堤用于解决桥头跳车效果明显。     

土工格栅在软弱路基处理中的应用

阐述了土工格栅的应用对地基土的加固原理及相应的地基的承载力计算公式,并通过工程实例介绍了其应用对于沉降、水平位移等方面的良好的调节作用.     

道路施工中土工格栅的运用分析

随着城市化进程地不断加快,我国的公路事业取得了巨大的发展,许多先进的施工工艺和施工设备也得到了广泛使用。本文分析了通过有效的措施和方法在土工格栅道路工程中增强道路桥梁工程的施工质量的同时增强公路企业的市场竞争力。     

土工格栅受力状况的测试技术

研制了测试土工格栅内力的传感器,介绍了其工作原理,构造和系数标定等过程.并结合某试验工程,就传感器的埋设方法及其受力状况的测试结果进行了叙述和分析.     

土工格栅在土质陡边坡的技术应用

在对旧路进行拓宽改造时,按常规坡率放坡,会遇到路基加宽部分坡角落在路旁边的水塘或河道中,增加处理难度和占地费用。介绍了天津杨北公路改建过程中,为避免占压河道,节省投资,首次采用加土工格栅的陡边坡,使其边坡率变小变陡。经过10 a使用,未出现任何问题,完全达到设计要求。     

土工格栅嵌锁力的理论计算方法探讨

针对土工格栅嵌锁力提出了一套简化的理论计算方法。通过对碎石填料和格栅作用模型的简化处理,给出了一种格栅与填料颗粒的单元嵌锁模式,并通过对该嵌锁模式下的填料颗粒的两种运动趋势—平移和转动进行讨论和分析,推导了不同条件下格栅的极限拉力,得出了最终的单元嵌锁力。     

谈垃圾填埋场渗滤液处理设计

采用ICP-AES技术检测和分析了重金属的类别与浓度,同时结合国内外最新研究讨论了垃圾渗滤液处理新技术,提出了该技术处理过程中存在的问题,并总结了生活垃圾的综合利用方法。