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Engineered capping systems are in most cases an indispensable and often the only efficient component required by the long-term safety concept for landfills, mine tailings tips and contaminated land. In Germany the composite liner is the main component of standard landfill cappings for municipal and hazardous waste landfills and the compacted clay liner (CCL) for landfills for inert or low-contamination waste. The composite liner is a technically highly effective but very expensive system. Research and experience has given rise to concern about the proper long-term performance of a conventional single CCL as a landfill capping. Therefore, alternative capping systems are discussed and applied for landfills and for the containment of contaminated sites. This paper gives an overview on various alternative engineered cappings and suitable systems for capping reflecting the state of the art and the expert view in Germany. According to the European Council Directive on the landfill of waste an impermeable mineral layer is recommended for the surface sealing of non-hazardous landfills and a composition of artificial sealing liner and impermeable mineral layer for hazardous landfills. In both cases a drainage layer thickness of at least 0.5 m is suggested. These recommendations should be interpreted flexibly and to some extent modified in the light of the experience and results presented in this paper.
Accurate and reproducible measurement of the structure and properties of high-value nanoparticles is extremely important for their commercialization. A significant proportion of engineered nanoparticle systems consist of some form of nominally core-shell structure, whether by design or unintentionally. Often, these do not form an ideal core-shell structure, with typical deviations including polydispersity of the core or shell, uneven or incomplete shells, noncentral cores, and others. Such systems may be created with or without intent, and in either case an understanding of the conditions for formation of such particles is desirable. Precise determination of the structure, composition, size, and shell thickness of such particles can prove challenging without the use of a suitable range of characterization techniques. Here, the authors present two such polymer core-shell nanoparticle systems, consisting of polytetrafluoroethylene cores coated with a range of thicknesses of either polymethylmethacrylate or polystyrene. By consideration of surface energy, it is shown that these particles are expected to possess distinctly differing coating structures, with the polystyrene coating being incomplete. A comprehensive characterization of these systems is demonstrated, using a selection of complementary techniques including scanning electron microscopy, scanning transmission electron microscopy, thermogravimetric analysis, dynamic light scattering, differential centrifugal sedimentation, and X-ray photoelectron spectroscopy. By combining the results provided by these techniques, it is possible to achieve superior characterization and understanding of the particle structure than could be obtained by considering results separately.
An approach to achieve “zero leakage” is discussed with respect to the experience in Germany, where strict regulations for landfill lining and capping systems have been developed and issued because of large environmental problems related to landfills that accumulated in the 1970’s and 1980’s. Using a thick, high quality HDPE geomembrane (GMB), which is installed free of residual waves and wrinkles in intimate contact with a compacted clay liner (CCL) or geosynthetic clay liner (GCL) of very low permeability, by a qualified, experienced, well equipped and properly third-party controlled installer and which are protected by heavy protection layers designed with respect to long-term performance of the GMB, may result in a liner or capping system of practically no leakage. This is demonstrated by analyzing results of measurements obtained from permanently installed leak detection systems in combination with HDPE GMBs. The survey is based on 32 German landfills with 1,276,500 m² of installed HDPE GMB.
The behaviour of HDPE geomembranes and installation quality control in geotechnical application
(2013)
The German Landfill Ordinance regulates the use of geosynthetics and other materials in the field of waste Containment Systems. It requires a certification of the geosynthetics by the BAM. The certification-guidelines define the state of the art by giving detailed requirements and specifications i the various geosynthetic products used in landfill constructions. According to the German Landfill Ordinance geosynthetic products have to fulfil their function for more than 100 years. Beyond, supported by an advisory board of landfill experts, BAM has developed installation requirements and demands on quality management for production, installation and third party control. The BAM is responsible to define tests and testing criteria for geosynthetics, to include provisions into the certification document and in addition to stipulate requirements with regard to installation procedure and quality management in Germany. All documents of the BAM such as certification guidelines, recommendations and testing specifications which are approved by the advisory board are published in German language on the website and in the Official Gazette*** of the BAM. For the certification one of the basic requirements is that the geosynthetic product is produced with well defined and well reproducible properties. Thus, a sophisticated quality management System is needed. In addition, not only production control, but also a quality assurance for the installation is necessary.
Like all plastic products, geocomposite drains (GCD) are susceptible to creep and creep rupture. The GCD is slowly and continuously deformed under long lasting shear and pressure forces. The thickness is reduced and thereby the water flow capacity. If the in-plane deformation reaches a critical value in the course of time, shear failure might occur. Likewise, if the thickness reaches a critical value the structure of the drain core might collapse. These effects are shown using data provided by the manufacturers of four different GCD. Long-term water flow capacity and the acceptable limits of shear stress and normal stress (pressure) with respect to shear rupture and drain core stability as well as the lifetime with respect to these failure modes are determined using standard test methods. The design of long lasting geotechnical structures has to take into account these characteristics of the long-tem performance of GCD.
Designing the performance of geogrids in reinforce soil constructions usually does not consider long-term behavior and possible failure modes of junctions between longitudinal and transverse ribs. How could behavior of junctions be included? To which extend is it necessary? On the conference Geo-Chicago 2016, Swan and Yuan presented an ultimate limit state equation for the short-term material resistance of junctions. We discuss limitations and suggest improvements to include long-term behavior of junctions. Nevertheless, the approach applies only to a specific mode of shear-tensile failure of junctions and only to strictly rigid geogrids. A new design concept presented in the same year by Jacobs on the conference GeoAmerica for the special case of the anchorage of geogrids, which reinforce capping system on long and steep slopes of landfills, tried to overcome these drawbacks. We discuss the aspects of this concept related to the long-term behavior
of junctions and the interplay between the load applied to junctions and the flexibility of longitudinal ribs. This interplay and the long-term junction strength determine the long-term behavior of geogrids.