Conference Agenda

<p>The PVC geomembranes are the most common used for dams. The success of a waterproofing system with geomembranes depends on the quality with which the seams are made. The seams have to be evaluated in terms of continuity/watertightness and mechanical strength, the latter being assessed by peel and shear tests.</p>

<p>Peel and shear tests are generally carried out according to the ASTM D 6392 standard, which, in case of PVC geomembranes, recommends a testing speed of 50 mm/min, for peel test, and 500 mm/min, for shear test. However, <em>in situ</em>, sometimes it is not possible to attain the testing speed suggested for shear test, mainly due to limitations of the testing machines routinely used. This raises questions about the acceptance / rejection of seams.</p>

<p>To address this issue, a research project is ongoing. Both single and double thermos‑fusion seams are being tested to shear strength at testing speeds ranging from 50 to 500 mm/min, according to ASTM D 6392 standard.</p>

<p>The locus-of-break codes of the seams, according the ASTM standard, are also being addressed in order to discuss its usefulness within the acceptance/rejection criteria for PVC geomembranes.</p>

<p>This paper will present and discuss the results obtained.</p>

<p>Geomembranes can be produced with or without surface texture. This choice is generally driven by design requirements, in particular the slope stability, but also the safety of users and wildlife. Overall, a bit less than half of textured geomembranes worldwide are produced by coextrusion, a bit more than a third are embossed, and a bit less than a fifth are sprayed with polyethylene filaments.</p>

<p>For coextruded textures, Blond and Elie (2006) have shown that there is a correlation between the height of the asperity, measured by ASTM D7466, and the shear-strength properties of the interface between the geomembrane and an adjacent material. Adesokan and Blond (2018) have shown that the density of asperity may also further influence the interface shear-strength properties. However, there is little information available on the performance of the two other texturing techniques frequently used for geomembranes, i.e., embossing the surface, or spraying it with polyethylene particles. Finally, there is a consensus on the limited performance of ASTM D7466 to adequately predict the performance of geomembranes with an embossed or a spray-on texture.</p>

<p>In this document, the various techniques used to create a surface texture on a polyethylene geomembrane are described. The results of an experimental program aiming at measuring their shear-strength properties against a geotextile and a soil is presented. Various methods used to characterize the different types of texture are exposed and criticized.</p>

<p>Finally, a universal strategy to qualify the performance of textured geomembranes is proposed, which can be used for quality control as well as to predict the long-term performance of the texture.</p>

<p>Geosynthetic Cementitious Composite Mats (GCCMs) are factory-assembled geosynthetic composites consisting of a cementitious material contained within layers of geosynthetics that becomes hardened when hydrated, and are primarily used to replace conventional concrete for erosion control and weed suppression applications. GCCMs are unique geosynthetic materials as their properties change from flexible to rigid once cured and in service. The cured cementitious layer also provides inherent physical properties to the GCCM including its compressive strength, initial (1^st crack) flexural strength and abrasion resistance. Assessing the performance of the cementitious layer within a GCCM typically falls outside the scope of conventional geosynthetic test standards. Similarly, testing of GCCM cementitious materials to conventional concrete standards at optimum water/cement ratios can also be unrealistic of in service GCCM performance, as the water applied in hydration is not controlled and GCCMs often cure in immersed conditions, increasing the water/cement ratio and decreasing the compressive strength of the cementitious layer. If a designer does not understand the test standards that GCCM manufacturers use to report their physical properties, there is a risk that they can specify an unsuitable GCCM material for their project.</p>

<p>ASTM D8364 ‘Standard Specification for GCCM Materials’ was published in March 2021 and provides assurance to designers of GCCM applications. This paper provides an assessment of ASTM D8364, reviewing the GCCM performance properties listed in the Classifications for GCCMs table and the importance of testing to the specified standards. Particular focus is given to why all GCCMs specimens should be cured by hydration by full immersion to ADTM D8030 and why the compressive strength should be determined to the GCCM specific test methodology in ASTM D8329. By Specifying GCCM Classification Types to ASTM D8364, designers can protect themselves from using GCCM test data that may not be representative of in field GCCM performance.</p>

<p>There has been significant developments in the accuracy, speed and availability of integrity surveys over recent years so that Geomembrane electrical integrity surveys have become a commonly used tool to assist in achieving low installed geomembrane defect rates and accordingly low seepage rates. There has also been a significant contribution from researchers analysing geomembrane seepage providing models which can be used to predict the effect of geomembrane defects for use in the design process. These models provide assistance in developing designs and construction strategies to reduce and even attempt to eliminate defects and seepage. Much of this work has been based around composite liner systems and particularly considering landfill applications where actual seepages are not easily measured. This paper examines a number of recent projects applying differing design concepts including double liner systems, and different materials. The correlation between defect rates and both construction methods and quality control strategies is reported. The database analysed includes a significant number of double lined containment systems which were subjected to geomembrane integrity surveys quantifying the as installed and post survey quality levels as well as quantifying actual seepage rates during the storage commissioning process. This data provides a valuable insight into and contemporary benchmark for achievable defect rates and seepage levels in liquid containment storages.</p>

<p>The Polyethylene geomembrane industry continues to evolve and enhance material formulations to meet the challenges of demanding containment system. There is increasing interest in characterizing these geomembranes when used in critical containment applications and this is often accompanied with increased quality assurance testing. A key test used to indicate the likely durability of a Polyethylene geomembrane is to measure its Oxidative Induction Time (OIT) according to either ASTM D 3895 for Standard OIT or ASTM D 5885 for High Pressure OIT. These tests can be undertaken on new un-aged samples, materials that have been artificially laboratory aged or specimens exhumed from the field.</p>

<p>Particularly with more advanced Polyethylene formulations the specimen preparation procedure for OIT testing can affect the measured OIT result making the comparison of different geomembrane formulations and the comparison of new and aged test results problematical. This paper reports on a systematic examination of different specimen preparation procedures on the measured OIT result for several different geomembrane formulations, multi-layer geomembranes and aged geomembranes. Specimen preparation procedure was also observed to have a significant effect on OIT test repeatability. Results are analyzed and suggestions made regarding specimen preparation procedures for advanced geomembranes.</p>

<p><em>Geosynthetic clay liners (GCLs) are factory-manufactured hydraulic barriers increasingly used in geotechnical, hydrotechnical, mining and environmental applications mainly for containment purposes. The type of construction, as well as the anticipated function, determines technical requirements that GCLs must fulfil. There are many laboratory test methods that could be used for the characterization of GCLs as a composite final product or their components (mineral and geosynthetic). Among other tests, free swell test (ASTM D5890) and Enslin-Neff water-absorption test (DIN 18132) are used for manufacturing quality control and as performance-based indicator for the mineral component i.e. bentonite clay. ASTM standard test method for swell index of clay mineral component of geosynthetic clay liners (ASTM D5890-19) appeared in revised form in 2019 giving precision information for within- and between-laboratory repeatability and reproducibility limits in terms of coefficients of variation. The paper will present the attempt to perform within-laboratory evaluation of measurement uncertainty in bentonite free swell and water-adsorption testing, to identify and quantify the most significant sources of uncertainty (sampling, environmental conditions, equipment etc.), and to evaluate some requirements from standard test method (influence of sufficient time and temperature for drying etc.). </em></p>

<p>The membrane behaviour of standard and enhanced bentonite contained in Geosynthetic Clay Liners has been regarded with great interest for applications in barrier systems since the presence of chemical osmosis will in general improve the containment properties of a GCL. Experimental evaluation of chemico-osmotic behaviour is essential to assess the existence and permanence of chemico-osmotic behaviour in GCLs. To this purpose, an apparatus able to perform chemico-osmotic diffusion tests on fine-grained soils or GCLs has been developed. The testing systems enables to determine the induced osmotic pressure (if any) across a GCL (or soil) specimen while maintaining a steady-state solute diffusion, under controlled stress or controlled volume conditions. The paper describes the main features of the systems and preliminary results that were obtained using a polymer-amended prehydrated GCL and a 20 mM KCl solution. The measured osmotic efficiency and solute diffusion coefficients were close to results in the literature on the same material under similar testing conditions, proving the system reliability. The system will allow investigating the influence of variables such as the GCL void ratio and solution composition on the chemico-osmotic performance of conventional and polymer-enhanced GCLs.</p>

This study investigates the resulting changes in the properties of a high-density polyethylene geomembrane (HDPE GMB) subjected to an accelerated UV (ultraviolet) ageing test. A commercially available GMB having a nominal thickness of 1.5 mm was exposed to UV radiation for varying durations for three years using an Atlas make UV weatherometer. Properties including thickness, density, melt flow index, tensile behaviour, oxidative induction time (OIT), crystallinity and microstructural changes using Fourier transform infrared (FTIR) spectroscopy were studied. The results showed that the thickness of GMB was not affected by UV radiation. However, the density and melt flow index values showed a significant variation. At the end of 26095 hours of exposure, OIT was reduced by more than half the value of the initial OIT. The degradation by cross-linking was verified from FTIR spectra which showed an increased crystalline content against the ageing time.

<p>Geomembranes sheets used in fluid containment applications are welded together in situ using a dual track hot wedge welder or extrusion welding. In dual track wedge welding, overheating can occur in the weld and still meet typical acceptance standards based on peel and shear strength. However, this overheating deplete antioxidants and contribute to a potential reduction in the service life of the geomembrane in the heat affected zone (HAZ) adjacent to the weld. This study examines the relationship between the welding quality and thickness on the production of the weld and any reduction in standard oxidative induction time (Std-OIT) for four HDPE geomembranes. The paper will then describe ageing tests being conducted on these different welds to evaluate the impact on the rate of antioxidants depletion post welding in the weld, the heat affected zone, and the parent material. Once standard OIT is depleted, the changes in physical properties also be monitored together with the high pressure OIT to establish if there is any relationship between retained HP OIT and weld longevity.</p>

<p>Geomembrane is defined as a synthetic material or bituminous reinforcement (sheets) with low permeability. The geomembranes are used in environmental, geotechnical applications and transport applications. The manufacturing process begins with the choice of its raw materials, including polymeric resin and various additives. Many standards and specifications have been used to perform tests on geosynthetics. These standards are, the international (ISO), German (DIN), French (AFNOR) and American (ASTM). In waterproofing applications such as containment of liquid / solid waste or landfills, any damage caused to the geomembrane may cause excessive flow compromising its function. Thus, there is a need to guarantee the function of the product, whatever the specific application. This is done through inspections verifying the product's Quality Control (QC) and Quality Assurance (QA). To guarantee QC and QA, some analysis are used, Thermo Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Dynamical Mechanical Analysis (DMA), Infrared Spectroscopy (IR) and others. None of them can simultaneously bring information about chemical characterization, identification of compounds through molecular mass, determination of markers, comparison with database or typical chemical profile. For this, mass spectrometry provides useful data for the identification and characterization of compounds, molecular mass and molecular formula, obtained by means of fragmentation patterns and information of presence or absence for various functional groups, and comparison with databases. In addition to mass spectrometry, the use of multivariate analysis, which in general can measure, explain and predict the relationship between variables and their impacts, collaborates with interpretation of data. However, the main objective of this work is characterize geomembranes obtained commercially from three different Brazilian companies. The mass spectrometry technique and multivariate analysis tools were used. Headspace extraction and solvent partition methods are used for volatile and semi-volatile compounds. Statistical tools such as PCA, cluster analysis and heatmap were applied to evaluate the results.</p>