垃圾填埋场土工合成材料界面摩擦特性的拉拔试验研究

土工合成材料与填料的界面特性是决定垃圾填埋场中衬垫系统与土工合成材料受力特性的重要因素。选择3种不同种类的土工合成材料,用砂土和黏土为填料,通过拉拔试验研究土工合成材料的界面特性。试验结果表明:界面的峰值剪切强度与峰值位移随着法向应力的增加而增加;土工合成材料与黏土之间的摩擦角较大;填料为砂土时,无纺布与填料间的摩擦角最大,EPDM次之,HDPE最小;当HDPE上下都铺无纺布时,界面的摩擦系数最小。     

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.     

A numerical modelling technique for geosynthetics validated on a cavity model test

Numerical modelling approaches can aid in designing geotechnical constructions involving geosynthetics. However, the reliability of numerical results depends on how the model is developed, the constitutive model, and the set of parameters used. By comparing the numerical results with experiment, the present work verifies a numerical modelling technique developed to model multilayered geosynthetic lining systems for landfills. The numerical modelling technique involves strain softening at interfaces and allows the axial stiffness of the geosynthetics to evolve as a function of strain. This work focuses on a two-dimensional finite-difference model, which is used to simulate three types of experimental tests: conventional uniaxial tensile tests, direct shear tests, and a large-scale test that was used to assess the overall mechanical behaviour of a reinforced geosynthetic system that spanned over a cavity. This reinforced geosynthetic system consisted of a 50 kN/m polyvinyl alcohol geogrid reinforcement embedded in a layer of sand, a geosynthetic clay liner, a high-density polyethylene geomembrane, and a non-woven needle-punched geotextile. The uniaxial tensile tests, direct shear tests, and the large-scale test were numerically modelled and the numerical results were compared with experimental results. The results of the numerical modelling technique presented very closely match the results of the three experimental tests, which indicates that the numerical model correctly predicted the measured data.     

A new constitutive model for textured geomembrane/geotextile interfaces

The paper presents a study of the frictional behaviour of geosynthetics used for municipal solid waste landfills. Direct shear tests of several geomembrane/geotextile interfaces were performed to investigate the shear behaviour. Furthermore, analytical and numerical models were developed to describe the observed behaviour, especially to simulate progressive geomembrane/geotextile interface failure and the factors controlling its significance.     

Prefabricated bentonite clay liners

The development and use of prefabricated bentonite clay liners is a relatively recent development, even for a technology as young as geosynthetics. There are four currently available commercial products, each of which consists of essentially dry bentonite clay agglomerates (with or without a dry, but water soluble, adhesive) placed on a geotextile or geomembrane carrier layer. Often a covering geotextile is used above the clay, and for two of the products, the entire ‘sandwich’ is needled throughout.

For landfill liner systems, the major use of these materials appears to be as the lower component of a composite primary liner. This use is particularly interesting in the light of response action plans (RAPs) which are being required by many regulating agencies. For landfill closure systems, these materials can readily form the lower component of a composite cap system. Of interest here is their possible capacity to follow subsidence of the landfill and their ability to deform in an out-of-plane manner.

With the newness and potential of prefabricated bentonite clay liners, however, comes a number of questions. This paper attempts to present these questions and the currently available answers regarding the various products. In concludes by giving a number of suggestions and cautions for field placement based on the authors' experiences to date.     

Rapid prototyping of geosynthetic interfaces: Investigation of peak strength using direct shear tests

Rapid prototyping offers a platform technology for investigations within the geosynthetics research and manufacturing sectors. This paper considers the application of rapid prototyping for the development of geosynthetic interfaces. The benefits and challenges of three rapid prototyping techniques (fused filament fabrication, selective laser sintering and laser thermal ablation) are considered and comparisons are presented between the three technologies. The paper then compares prototyped models of geomembrane texturing to those of a factory sourced reference geomembrane, leading on to a systematic geometric assessment using laser sintered model geomembranes. The geometric assessment highlights the benefits of hooked geomembrane asperities to interact with geotextiles in low normal stress applications, with a 69% increase in peak shear strength reported for hooked asperities, compared to the factory reference geometry. Asperity spacing is shown to influence the measured shear strength, with an increase for a geomembrane geotextile interfaces with closer asperities and an optimum spacing observed for geomembrane clay interfaces, below which the failure plane slides over the top of the texturing. Increases in asperity height correlated to smaller than expected increases in shear stresses for both geomembrane-geotextile and geomembrane clay interfaces.Whilst current rapid manufacturing techniques are shown to offer the ability to test the influence of variables on the performance characteristics of geosynthetic materials, the limitations of each technique, polymer utilised and resulting chemical and physical behaviour of the sample must be understood to allow these techniques to be successfully deployed.     

Evaluation of interface shear strength of composite liner system and stability analysis for a landfill lining system in Thailand

The paper presents the case history of laboratory evaluation of the interface shear strength properties of various interfaces encountered in a modern day landfill with emphasis on proper simulation of field conditions and subsequent use of these results in the stability analyses of liner system. Over 70 large direct shear tests were systematically conducted to evaluate the interface shear strength properties of composite liner system using project specific materials under site specific conditions, being used at non-hazardous and hazardous landfills project situated in Sa Kaeo Province, Thailand. The critical interfaces were located between the geotextiles and the smooth geomembrane (GM), the smooth GM and the geosynthetic clay liner (GCL), and the smooth GM liner and the compacted clay liner (CCL) with the interface friction angles ranging from 6.5° to 10.5° for dry conditions and 6.5° to 9.5° in wet conditions. The residual shear stress for these interfaces was attained at a displacement less than 4 mm. Three methods, namely, limit equilibrium method (LEM), limit method (LM), and the simple composite column (SCC) approach were used to evaluate the tensile loads induced in the geosynthetic components. The SCC approach proposed by Liu, C.N. [2001. Tension of geosynthetics material regarding soils on landfill liner slopes. Proceedings, National Science Council ROC(A), 25(4), 211–218] that takes into account the force equilibrium as well as displacement compatibility yielded satisfactory results. The factor of safety for geosynthetic components in the liner was found to be greater than 3.0 for both types of landfill.     

垃圾填埋场终场腾发覆盖系统的研究进展

垃圾填埋场的传统覆盖形式为压实黏土、土工合成材料、土工膜或由这些材料组合而成的屏障型覆盖系统,由于垃圾降解和固结沉陷等原因,几乎所有屏障型覆盖系统在长期使用过程中都可能破坏失效。近年来,腾发覆盖作为一种替代覆盖技术在美国的垃圾填埋场得到广泛应用。腾发覆盖由一层植被土构成,它利用非压实土层储蓄渗入的降水、依靠植物的蒸腾和土壤蒸发消耗土壤水,从而实现渗沥污染控制。腾发覆盖的植被宜采用灌木和草皮混合形式,覆盖土层宜采用壤土或黏壤土,土体密度宜为1.1～1.5g/cm3,土层厚度取决于植被和当地气候。腾发覆盖是一种经济、实用、易于建造和维护的生态覆盖技术,但不宜用于蒸发量∶降水量〈1.2的沿海地区。     

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%.     

兰州某垃圾填埋场场地岩土工程条件评价及防渗处理方案建议

通过对垃圾填埋场场地岩土工程条件的分析,对垃圾填埋场拟采用的防渗方案进行了比选,提出了粘土铺盖加HDPE（高密度聚乙稀）防渗膜的综合防渗方案,对同类工程防渗设计具有参考意义。     

A multi-camera based photogrammetric method for three-dimensional full-field displacement measurements of geosynthetics during tensile test

Conventional methods for measuring the deformational response of geosynthetics, such as the linear variable differential transformers (LVDTs), strain gauges, and extensometers have several limitations in fully determining the complete strain distribution in geosynthetics. This paper presents a multi-camera based photogrammetric method to track the 3D full-field displacements of geosynthetics during tensile tests. The proposed method extends the conventional one-camera based photogrammetry for static object measurements to multi-camera-based photogrammetry for object measurements with continuous movements or deformations. It is non-contact, cost-effective, highly accurate, and capable of measuring the 3D full-field displacements of the geosynthetics. A tensile test on a geogrid specimen was performed to verify the effectiveness and accuracy of the proposed photogrammetric method. The results from the tensile tests using both the proposed method and conventional methods, such as machine-controlled displacement measurements and extensometer, were presented and compared. It was observed that the average absolute difference between the proposed photogrammetric method and the machine-controlled movements of the bottom clamp was 0.25%, and the average absolute error was 0.038 mm. The average difference in measurements made by the proposed method and extensometer was 0.07%. It was further found that the proposed method can provide more comprehensive input, such as the complete strain and modulus distributions in the geosynthetics, for a probability-based geosynthetics design.     

Performance issues of barrier systems for landfills: A review

The objective of the paper is to give an update in key topics related to performance issues of barrier systems for landfills. The objective of using barrier systems is to minimize the impact of contaminants on the surrounding environment. To achieve this goal puncture protection of the geomembrane must be ensured. An update is first given with respect to this matter. The question of the stability on slope of geosynthetic barrier systems is then discussed and an insight is given in modeling and laboratory measurement of parameters required to perform reliable modeling, especially as regards the case of piggy-back landfills. Geotechnical centrifuge modelling tests are very important for simulation of landfill stability induced by the failure of geosynthetic interfaces and validation of complicated numerical models, especially for the high food waste content landfills. The seismic design or assessment of landfill stability with respect to geosyntheics needs to be investigated. Finally, the question of transfers through bottom barrier systems is addressed, giving an update especially in the analytical solutions developed in the past 10 years in China in this matter. The breakthrough time based design method for landfill liner system was then summarized. The behaviour of double-liner system and its simplified performance-based design method should be further investigated in the high food waste landfills with high leachate level.     

土工合成材料在城市固体垃圾填埋场中的应用

对一系列新型化工产品———土工合成材料在城市固体垃圾填埋场中的应用 ,特别对其中土工织物 (GT)、土工膜 (GM)、土工合成材料粘土垫 (GCL)、土工网 (GN)、土工复合材料 (GC)以及土工泡沫 (GF)等在填埋场衬垫、封盖系统中的应用作了全面的总结 ,详尽地分析了各种材料的主要用途     

Interaktionsverhalten von Geokunststoff und Boden unter statischen und zyklischen Beanspruchungen

Interaction behaviour of geosynthetics and soil under static and cyclic loadings. When used in reinforced structures, bridging of voids or abutments geosynthetics are exposed to static and cyclic loadings from traffic, machines and construction work. For the proof of internal stability in these structures detailed knowledge of the interaction behaviour between the geosynthetic and the surrounding soil in the anchorage area is required. No sufficient experience of the behaviour under cyclic loadings is available at the moment. In this contribution information on cyclic loadings of reinforcing elements is given, a testing framework for the examination of this topic is presented and key parameters are extracted. A method for the determination of cyclic displacements and a universal design concept for the anchorage area of geosynthetics are derived from the presented test results.     

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.     

Dynamic friction and the seismic performance of geosynthetic interfaces

The stability of geotechnical structures which contain geosynthetic interfaces is closely linked to the shear strength between the geosynthetics themselves, both in static and dynamic conditions. Static friction is the maximum interface shear strength mobilised before displacement, whereas dynamic friction is related to the kinematics of the displacement itself. In polymer materials, dynamic friction may be widely variable, depending on the type, geometry and integrity of the surfaces in contact, as well as on the intensity and time-history of the seismic signal. This means that predicting interface shear strength is not simple. This paper focuses on the evaluation of dynamic interface shear strength between geosynthetics, using the results of both inclined plane tests and shaking table tests; this latter test also provided a means to analyse interface behaviour under the conditions of real seismic records. To this purpose, two common geosynthetic interfaces, which exhibit different behaviour under dynamic loading, were tested. One interface was a smooth HDPE geomembrane in contact with a nonwoven polypropylene geotextile, while the second was a textured HDPE geomembrane in contact with a different type of nonwoven polypropylene geotextile.The test results shows that dynamic friction mobilised during seismic events depends on the relative speed according to the same law outlined by the free sliding tests and by the shaking table tests carried out with sinusoidal base motions. Moreover, for the two different types of studied interfaces dynamic friction may be greater, lesser or equal to the static friction and the assumption of a constant value of dynamic friction does not lead to an accurate prediction of the seismic displacements under various earthquakes.     

我国四类衬垫系统防污性能的比较分析

对我国填埋场采用的四类衬垫进行了防污性能的比较分析。评价参数包括渗漏率、污染物击穿时间及衬垫系统底部浓度值。除了2m压实黏土衬垫(CCL)外,其余3种均为包含土工膜(GM)的复合衬垫。分析模型采用了污染物通过有缺陷膜复合衬垫的一维运移解析解。以镉离子(Cd2+)为渗滤液中重金属离子的代表;以苯为其中挥发性有机污染物的代表。研究表明土工复合膨润土垫(GCL)复合衬垫的渗漏率最小,2m黏土最大,两者的差别可在3～5个数量级。GCL复合衬垫对重金属离子具有较好的防污性能,尤其是在高水头及复合衬垫接触较差的情形。厚度较大的2m黏土对挥发性有机污染物的防污性能较好,其击穿时间要比GCL复合衬垫大2～3个数量级。随着水头的增大,CCL复合衬垫的防污性能逐渐地优于2m黏土。在10m水头作用下,CCL复合衬垫底部的100年浓度可比2m黏土小近一个量级。单层膜衬垫的防污性能较差,不适合作为填埋场的衬垫系统。控制填埋场复合衬垫的施工质量和渗滤液水头尤为重要。     

Properties of geosynthetics exhumed from a final cover at a solid waste landfill

Samples of geocomposite drain (GCD), geomembrane (GM), and geosynthetic clay liner (GCL) were exhumed from a final cover at a solid waste landfill to assess their condition after 4.7–5.8 yr of service. Permittivity of the GCD diminished by a factor of 3.9, but the transmissivity was higher than published by the manufacturer. Ply adhesion of the GCD diminished by a factor of 2.0. Geonet ribs in the geocomposite drain (GCD) contained a light coating of fines and plant roots, but there was no evidence of significant clogging. The geotextile on the upper surface of the GCD met the commonly used criterion for filtration (AOS < 0.6 mm for adjacent soil with <50% fines), indicating that this filtration criterion was satisfactory. Tensile yield strength of the GM diminished by a factor of 1.2, but the melt flow index was unchanged and the oxidation induction time exceeded the manufacturer's specification. GCD-geomembrane interface strength appeared unchanged. Four GCL samples had hydraulic conductivities 1000–10,000 times higher than the hydraulic conductivity measured during construction, whereas hydraulic conductivity of the other seven samples was practically unchanged. Based on these observations, the following reduction factors are suggested for installation damage and near-term service conditions (<6 yr) for the geosynthetics used at this site: GCD permittivity or transmissivity – 4.0, GCD ply adhesion – 2.0, geomembrane tensile strength – 1.5, and GCD-geomembrane interface friction – 1.0. No recommendation is made regarding a factor for the hydraulic conductivity of GCLs.     

Field study and numerical modelling for a road embankment built on soft soil improved with concrete injected columns and geosynthetics reinforced platform

Generally numerical modelling can provide an accurate and cost-effective approach to understand the behaviour of geosynthetic-reinforced column-supported embankment. When the problem geometry cannot be simplified to the two-dimensional plane-strain or axisymmetric, a full three-dimensional solution is required to obtain sensible results. This study presents a modelling of the geosynthetic-reinforced composite ground supporting a road embankment. Response of soft soil is captured by adopting Modified Cam-Clay model. In addition, Hoek-Brown constitutive model is considered to simulate non-linear stress-dependent yield criterion for Concrete Injected Columns (CIC) that describes shear failure and tensile failure by a continuous function. To assess whether the proposed numerical model can capture real behaviour of composite ground, field monitoring data of deep soft clay deposit improved by CIC from Gerringong Upgrade is used to validate the model. The settlement and lateral displacements of ground, stress transferred to column, and pore water pressure results for the embankment during and after the construction, measured using the field instrumentations including settlement plates, inclinometers, earth pressure cells on CIC, and pore pressure transducers, are compared with numerical predictions. In addition, the numerical results provide insights to investigate load transfer mechanism in the composite ground, capturing response of soil – column - embankment system.     

热-水力-力学-传质耦合过程模型及工程土障数值模拟

提出了一个非饱和多孔介质中的热 -水力 -力学 -传质耦合过程模型。利用文献 [1]中提出的热 -水力 -力学本构模型 ,对工程土障系统进行数值模拟。数值模拟结果显示了环境条件对废物场中的热量产生和传输过程对工程土障中水力 -力学行为的影响以及可能在工程土障中产生塑性应变 ,导致土障破坏。污染物浓度分布的数值结果显示了温度与降水过程对污染物随地下水向土障周边自然环境渗透的倾向。数学模型及所发展的有限元求解过程可以为评估土障系统长期工作的有效性和土障系统的合理设计提供有力的工具