Destructive testing of geomembrane seams: Shear and peel testing of seam strength

An essential step to assure the proper long-term performance of a geomembrane liner that is in the process of being installed is 100% inspection of the seams to ensure their continuity. This step must be complemented with destructive testing of the seams to ensure their strength and integrity. At the present time, the principal destructive tests of seams involve strategic sampling and testing of the seams in accordance with standard ASTM methods for seam strength in shear and peel modes. This paper describes the seam testing of the different types of geomembranes and discusses specific tests that are used. Also discussed are the variables that are involved in the testing and the requirements that should be stated in the specifications in order to assure full understanding of the acceptance criteria and the requirements of quality control and quality assurance. The results of testing current geomembranes are presented. Finally, some limitations of destructive testing of seams are discussed.     

Geomembrane factory and field thermally welded seams comparison

This technical paper presents a unique comparison of geomembrane factory and field welded thermal seams for a large off-stream water reservoir project. The results of the comparison show that factory welded seams exhibit higher seam peel and shear strengths at yield, less variability, and more consistency than field welded thermal seams. In particular, the results show that factory seams are about 10% stronger than field seams in shear and about 9% stronger in peel strength at yield. More importantly, this resulted in 100% of the factory welded seams passing the project seam strength requirements even though the factory welding speed was 1.1–1.6 times faster than the field welding speed. Conversely, about 25% of the field welded seams did not pass the initial specified field seam shear strength requirement, which caused significant delays, scheduling, and other construction issues. As a result, the field seam shear strength requirement was reduced from 9.6 kN/m to 8.2 kN/m to increase the number of field seams that achieved project requirements. Because the geomembrane was primarily factory fabricated, there were about 78% less field seams on this project than if the geomembrane was entirely field fabricated.     

Bureau of reclamation experiences with PVC seams

The Bureau of Reclamation has been using polyvinyl chloride (PVC) plastic in its buried membrane canal lining work for over 20 years. Results of tests conducted on samples of inservice linings indicate that the factory-fabricated seams retain excellent shear and peel strength properties with no apparent signs of deterioration. The practice of using a 1-m overlap unbonded PVC field seam proven has adequate for most irrigation canal lining applications, but would not be suitable for applications requiring 100% seepage control. Results of laboratory investigations conducted in conjunction with a study on the underwater lining of operating canals with PVC indicate that an adhesive formulated for the repair of vinyl swimming pool liners can be used to make underwater PVC field seams. Results of these investigations also indicate that field seams made in the dry can achieve enough early peel and shear strength development (within 15 min) for placement underwater.     

Durability of chlorosulfonated polyethylene geomembrane seams after accelerated aging tests

Accelerated aging tests have been conducted on seam specimens prepared by the different methods used to seam chlorosulfonated polyethylene (CSPE) geomembrane. These included factory seams prepared by dielectric seaming, by hot air and with a bodied solvent as well as a field seam made with a bodied solvent. Accelerated aging tests were conducted in hot air at 100°C and in a 63°C Xenon Arc Weather-O-Meter. Shear strengths of seams increased significantly during the early aging exposures, as the CSPE cured, and they remained at the higher level for the duration of the tests. This was true for both potable and industrial CSPE grades.     

土工膜焊缝剪切强度与充气时间和充气压强的关系

土工膜焊缝剪切强度是整个防渗结构可靠性保障的关键因素之一。为了得到充气时间和充气压强对土工膜焊缝质量的影响,本文选择七种不同厚度的HDPE土工膜在不同充气时间和充气压强条件下进行焊缝剪切强度试验。试验结果表明:相同充气时间和充气压强条件下,土工膜焊缝剪切强度随着土工膜厚度的增加而增大,且曲线变化几乎一致;无论充气压力多少,充气时间长短,相同土工膜厚度试验条件下,不同厚度的HDPE土工膜在焊缝剪切强度方面表现出良好的稳定性,所有试验组的焊缝剪切强度值大小及其变化相近,剪切强度变化系数最大为6.72%,最小为0.81%,充气压力和充气时间对土工膜焊缝剪切强度影响很微小;土工膜焊缝剪切破坏主要发生在焊缝区域与土工膜母材的连接处薄弱部位,应当引起重视。     

Concerns regarding polyethylene geomembrane seams: One owner's perspective

The primary goal of an owner when constructing geomembrane liners at waste disposal facilities is the long-term protection of the environment. This paper presents the concerns of one owner regarding how to assure that the seams which join the geomembrane sheets provide the same level of integrity as the parent material. Discussions of concerns regarding seam strength, ductility, chemical compatibility, installation, testing, and resistance to stress cracking are presented. Also presented are procedures specified by one owner which we feel will help alleviate some of the prior mentioned concerns.     

Effect of soil compaction conditions on geomembrane-soil interface strength

A laboratory investigation was recently undertaken to evaluate the shear strength of the interface between a cohesive soil used for linear construction and a high-density polyethylene (HDPE) geomembrane. In the investigation, the interface shear strength was measured in a direct shear apparatus. The compaction water content and dry unit weight of the soil were varied in each test. It was found that the shear strength of the interface between these two materials is strongly affected by the compaction water content and dry unit weight of the soil. It is concluded from the test results that the soil compaction conditions strongly influenced the interface shear strength and this factor, among other, should be carefully considered during design.     

Laboratory assessment of Alaska aggregates using Micro-Deval test

Aggregates suitable for use in asphalt concrete (AC) pavement construction must meet durability criteria. Thus, it is critical to select appropriate tests to properly characterize aggregate durability. In Alaska, durability tests currently being used for aggregates in AC pavement include Los Angeles (LA) abrasion test, sulfate soundness test and Washington degradation test. However, there have long been concerns arising over Washington degradation test used as an acceptance tool, motivating pavement practitioners to seek more suitable alternatives. This paper presents a study to investigate the feasibility of using Micro-Deval test, commonly used in other states, to evaluate the durability of Alaskan aggregates in AC pavement as well as its potential to replaceWashington degradation test. Micro-Deval test,Washington degradation test and other tests currently specified in Alaska were conducted on aggregates from 16 batches representing statewide sources. Based on the testing results, it is found that using Micro-Deval test for durability assessment of Alaska aggregates was feasible and reproducible, and a high potential was revealed to use Micro-Deval test to replace Washington degradation test in Alaska. It is recommended that Micro-Deval test be considered as an additional test for a certain period, but in the long run should be used along with current LA abrasion and sulfate soundness tests to provide a more desirable durability assessment of Alaska aggregates used in AC pavement.     

Technical note on hot air seaming of high-density polyethylene geomembranes

Hot air fusion welding is widely used as a secondary seaming method for welding high-density polyethylene (HDPE) geomembranes, although seldom as a primary seaming method. This method is based on a very simple principle and can withstand comparison with the other main seaming methods. However, the strength and long-term durability of seams made with this method are still poorly known, and should be explored, as compared to the other welding methods.     

Quality assurance of geomembranes used as linings for hazardous waste containment

The lining of a facility for storing or disposing of hazardous materials or wastes on land must serve as an effective barrier to prevent potential contaminating species from migrating into the ground and the groundwater. The process from the design phase through the manufacture of a polymeric geomembrane to its installation and acceptance as a liner involves many steps that must be controlled in order to assure the ultimate effectiveness of the lining.

In this paper, a program of quality assurance and quality control involved in the critical steps in the process of constructing a lined waste disposal facility from its design through the final acceptance is described. Included are design, geomembrane selection and compatibility testing, specification, raw materials, geomembrane manufacture, panel fabrication, shipment to field site, inspection, installation and performance testing of the lined facility. Emphasis is placed on factors and properties of geomembranes that relate to service performance and must be controlled. The properties include overall thickness, thickness of coatings above threads, composition control, crystallinity, carbon black content, ply adhesion and seam integrity and strength.     

Shrinkage characteristics of heat-tacked GCL seams

The behavior of heat-tacked GCL seams under cyclic wetting and drying is examined. It is shown that the transverse shrinkage behavior of heat-tacked seams was similar to that observed in previous shrinkage tests performed on unseamed GCL. It is shown that the heat-tacked seam has strength comparable to the GCL adjacent to the seam and hence it is likely the strength of the GCL itself that will govern failure of the GCL in applications where there can be significant shrinkage. The strength of the heat-tacked seam subjected to 40 wet-dry cycles was at least as high as that of virgin heat-tacked samples, suggesting that 40 wet-dry cycles did not weaken the heat-tacked seam. After 40 cycles, the samples remained heat-tacked, suggesting the technique has promise as one method of preventing panel shrinkage for GCLs highly susceptible to shrinkage. It is noted that these tests are small-scale laboratory tests, under idealized conditions, and that the behavior in the field may differ due to more extreme conditions that may occur in the field and due to the greater amount of material between seams available to shrink and hence induce forces in the heat-tacked GCL seam.     

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.     

预制柱水平缝滑移破坏机理研究

应用中国规范及日本规范水平缝抗剪承载能力计算公式计算了六种常用截面、四种剪跨比、四种轴压比共96组截面的预制柱的承载能力,并对中日规范进行分析总结,提出改进的水平缝抗剪承载能力的计算公式;通过ABAQUS软件进行数值模拟,对改进的公式进行验证。结果表明：在小轴压比下,例如0.1时,预制柱会发生水平缝的剪切滑移破坏;中国规范关于水平缝的抗剪承载能力公式表明滑移破坏不可能发生,与实际结果有较大差异,其准确性有待进一步研究;文提出的改进的水平缝的抗剪承载能力公式与数值结果吻合较好,准确合理。     

坝坡内置光纤土工膜的膜–土界面亲和性试验分析

光纤土工膜是具有破损定位功能的新型防渗材料。为了研究红土大坝中的光纤土工膜对坝坡稳定的影响,进行剪切强度试验和可调斜坡模型的抗滑试验,获得各种工况组合下膜–土界面的黏聚力、内摩擦角、滑动坡比、摩擦系数等数据。与纯粹红土组、红土内置复合土工膜组的数据进行比对分析,结果表明:光纤土工膜与红土的亲和性足以满足抗剪要求;光纤土工膜作为防渗体嵌入坝坡,在实际工程条件下的抗滑安全性能不低于传统土工膜,能够满足规范要求。     

波纹钢板纵向接缝环槽铆钉连接与高强度螺栓连接受剪性能试验研究

与高强度螺栓连接相比,环槽铆钉连接具有预紧力不易损失、耐久性好等优势,具有替代高强度螺栓用于波纹钢板纵向接缝的可行性。为便于实际工程应用,需要对其受剪性能进行研究。以波形、板厚与连接件个数为参数设计了6组36个波纹钢板纵向接缝的轴压试验,包括两组单波波纹钢板环槽铆钉连接接缝、两组四波波纹钢板环槽铆钉连接接缝以及两组四波波纹钢板高强度螺栓连接接缝。波纹钢板波形尺寸分别为150 mm×50 mm、380 mm×140 mm,板厚分别为6、7 mm和8 mm。同时考虑波形和铆钉直径的影响,对四种连接形式的32个环槽铆钉进行了预紧力试验。主要从预紧力和受剪承载力两方面对两种连接形式进行了对比,并研究了钉群效应对于环槽铆钉连接纵向接缝承载力的影响。结果表明：强度等级相同的环槽铆钉预紧力明显高于高强度螺栓预紧力,环槽铆钉接缝在试验加载过程中未出现类似于高强度螺栓接缝的预紧力损失、连接松动现象,前者具有更大的受剪承载力和更好的延性。按JGJ 99—2015《高层民用建筑钢结构技术规程》计算波纹钢板环槽铆钉连接纵向接缝承载力偏于保守。考虑钉群效应的影响,建议采用JGJ 99—2015计算孔壁承压承载力...     

Experimental study on shear capacity of corrugated steel plate-longitudinal seams with ring groove rivet connection and high strength bolt connection

与高强度螺栓连接相比，环槽铆钉连接具有预紧力不易损失、耐久性好等优势，具有替代高强度螺栓用于波纹钢板纵向接缝的可行性。为便于实际工程应用，需要对其受剪性能进行研究。以波形、板厚与连接件个数为参数设计了6组36个波纹钢板纵向接缝的轴压试验，包括两组单波波纹钢板环槽铆钉连接接缝、两组四波波纹钢板环槽铆钉连接接缝以及两组四波波纹钢板高强度螺栓连接接缝。波纹钢板波形尺寸分别为150 mm×50 mm、380 mm×140 mm，板厚分别为6、7 mm和8 mm。同时考虑波形和铆钉直径的影响，对四种连接形式的32个环槽铆钉进行了预紧力试验。主要从预紧力和受剪承载力两方面对两种连接形式进行了对比，并研究了钉群效应对于环槽铆钉连接纵向接缝承载力的影响。结果表明：强度等级相同的环槽铆钉预紧力明显高于高强度螺栓预紧力，环槽铆钉接缝在试验加载过程中未出现类似于高强度螺栓接缝的预紧力损失、连接松动现象，前者具有更大的受剪承载力和更好的延性。按JGJ 99—2015《高层民用建筑钢结构技术规程》计算波纹钢板环槽铆钉连接纵向接缝承载力偏于保守。考虑钉群效应的影响，建议采用JGJ 99—2015计算孔壁承压承载力时乘以1.4的增大系数，计算环槽铆钉受剪承载力时乘以1.1的增大系数。     

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.     

大型斜面剪切仪的研制和试验

位于垃圾填埋场斜坡上的衬垫结构在垂直应力作用下沿斜坡滑移的剪切状态与底坡上衬垫结构的不同,为了模拟斜坡上衬垫结构间剪切特性,研制了斜面剪切仪。通过对标准砂和黏土的大型斜面和普通直剪剪切试验,发现两种试验得到的标准砂和黏土剪切应力位移特性基本相同,强度指标也相同。在此基础上,进行了光面HDPE土工膜与黏土复合衬垫界面斜面剪切试验,得到的剪应力与正应力比-位移曲线均有峰值和峰值后的软化现象。斜面剪切试验的特点是能够得到剪切面上法向应力和剪切应力同时增加的变化规律,可以揭示更详细的剪切特征,这有利于分析剪切过程中剪切面上法向应力和剪切应力的特性,如剪切面上法向应力和剪切应力变化规律以及剪切面上法向应力和剪切应力比的变化规律。     

水利工程土工膜耐老化性能的探讨

工程地处在寒冷和严寒地区,聚乙烯土工膜的耐低温、抗老化性能较好,可广泛采用。工程采用黑色中厚聚乙烯复合土工膜,具有防渗和平面导水的综合功能,抗拉强度高,抗穿透和抗老化等性能好,可不设过渡层,适用于地质及水文地质条件差、基土冻胀性较大及标准较高的渠道防渗工程。     

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.