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Was gibt es Neues? In diesem Beitrag wird über den aktuellen Stand bei der Zulassung von Geokunststoffen berichtet. Was die erteilten Zulassungen selbst anbelangt, so kann sich jeder an Hand einer Liste im Internet1 informieren. Dort findet man auch alle Dokumente zur Zulassung. Im Folgenden geht es daher um einige aktuelle fachliche Themen und zugehörige Fragen, die bereits in der obigen Zusammenfassung umrissen wurden.
Auch Kunststoffdränelemente sind wie alle Kunststoffprodukte für Kriechen und Stabilitätsversagen anfällig. Ein Kunststoffdränelement verformt sich unter langanhaltender Druck- und Scherbelastung allmählich. Dabei werden die Dicke und damit auch das Wasserableitvermögen reduziert. Wenn die Verformung parallel zur Ebene im Laufe der Zeit einen kritischen Wert überschreitet, kann es zum Scherversagen kommen. Das Kunststoffdränelement kann auch Zusammenbrechen, wenn die Dicke des Produktes einen kritischen Wert unterschreitet. Diese Effekte werden an Hand von Daten von Herstellern von vier verschiedenen Produkten beschrieben. Das Langzeit-Wasserableitvermögen und die akzeptable Grenzen für die Scher- und Normalspannung vor dem Hintergrund von Scherversagen und Dränkemstabilität und die Lebensdauer in Bezug auf diese Versagensmechanismen werden durch Zuhilfenahme standardisierter Prüfverfahren bestimmt. Diese Eigenschaften von Kunststoffdränelementen müssen bei der Planung dauerhafter geotechnischer Bauwerke berücksichtigt werden. Zudem wird kurz auf das Qualitätsmanagement bei dem Einbau und der Lagerung der Produkte auf der Deponiebaustelle eingegangen.
The German landfill ordinance regulates the use of geosynthetics, polymers and leak detection systems (LDS) in the field of landfill engineering in Germany. It governs the certification process and sets a framework for the requirements on these products. The certification guidelines of the BAM Federal Institute of Materials Research and Testing turn these requirements into detailed technical specifications and associated test procedures. The present paper describes the procedure of developing certification guidelines for LDS by BAM and its advisory board. The requirements for the certification of LDS under the terms of the new German landfill ordinance with regard to operation and capability are listed and the technical criteria are described. The performance test for LDS used in connection with geomembranes is discussed in detail.
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.
Geogrids, which are installed to prevent sliding failure on long and steep slopes, have to be safely anchored. The design and calculation of the anchorage is based on simple design rules. Basically, it is assumed that the pull-out resistance is proportional to the soil shear strength, the vertical load and the anchoring length and that the soil-reinforcement coefficient of proportionality as determined in pull-out tests is typically in the range between 0.5 and 1. Based on an extended version of a model for the soil-geogrid interaction, which was described by Ziegler and Timmers (2004) and Sieira et al. (2009), the physical assumptions and limitations of these rules are discussed. For those geogrids, for which the passive thrust mobilization of earth pressure by the displacement of the transversal or bearing force grid elements substantially contributes to the pull-out resistance, the mechanical strength of the junction between longitudinal and transversal elements is of crucial importance. The relation between mechanical properties of the junction, the flexibility of the longitudinal grid elements, the surface friction and the finally achieved pull-out resistance is exemplarily shown by a model calculation. It is included, that due to aging and creep the short-term junction strength may be significantly lower than the long-term strength. There is a certain critical pull-out resistance and an associated critical anchorage length. Both are determined by the strength of the junction embedded into the soil and are independent from the actually installed anchorage length. For a safe design it is not allowed to go beyond that limit. This requirement restricts the range of application of the common design rules. It follows that not only the long-term strength of the longitudinal elements has to be considered and quantified by reduction factors but also the long-term strength of junctions. These limitations have to be observed to achieve a safe design of the anchorage. Preliminary design rules are discussed.
The German landfill ordinance includes a certification requirement for geosynthetics used in landfill liner and capping systems. The certification guidelines describe the basis for the design of geosynthetics used in landfill construction. According to the rules which are usually applied, the thickness of the filter geotextile has to be at least 30 times the characteristic opening size O90. Filter geotextiles which are often used in geocomposite drains have a mass per area of 200 g/m² and do not fulfill this requirement.
In this paper modified filter criteria for geosynthetics are presented with a particular focus on These geotextile filters in geocomposite drains.
Data from four samples of commercially available PET geogrids (made either of yarns or bars), which were measured by BAM or other institute, are analyzed to discuss the procedure and problems of determining the chemical reduction factor RFCH associated with a certain service life. Estimates from Arrhenius extrapolation usually have very large statistical errors. The level of confidence must therefore be specified. A reliable estimate requires data from immersion tests below the glass transition temperature of PET. To extrapolate the time of reductions for each reduction factor at such low temperatures, one has to know the functional form of the mechanical degradation curve. It is shown how the degradation curve of the tensile strength may be obtained by determining the relation between increase in concentration of carboxyl end group (CEG) and decrease in tensile strength. Therefore, experimental studies to determine the chemical reduction factor should be accompanied by the measurements of the CEG concentration and the intrinsic viscosity. Furthermore, such measurements allow a non-ambiguous determination of the molecular mass. Hydrolytic molecular degradation will proceed continuously even at 20 °C with half-life of the inverse of the CEG concentration of 40–100 y. Nevertheless, small chemical reduction factors at a lifetime of 100 y are obtained with high level of confidence for materials with low initial CEG concentration and high molecular mass. This is shown by pooling data from samples with comparable CEG concentration, molecular mass and above all comparable intrinsic relation between increase in CEG concentration and decrease in strength. Therefore, the recommendation of ISO TR 20432, Table 2, for chemical reduction factors seems to be applicable to PET geogrids with index properties well below the one specified by the technical report. Whether these index properties are actually a sufficient condition to have small chemical reduction factors even at a very long service life is still an open question. The determination of chemical reduction factor should be based on aging experiments, at least for products with index properties close to the limiting values for the following reasons. (1) Even so standards are available, results of different laboratories on absolute values of CEG concentration and number averaged molecular mass differ to a certain extent. (2) Other factors, like crystallization, affect the mechanical degradation significantly. (3) There is no universally applicable form of the mechanical degradation curve.
In absehbarer Zeit werden CE-gekennzeichnete Geovliesstoffe, Geogewebe, geosynthetische Dränelemente und Geogitter aus Kunststoff erhältlich sein, bei denen die CE-Leistungserklärung den Hinweis enthält 'dauerhaft für bis zu 100 Jahre' oder sogar 'dauerhaft für mindestens 100 Jahre'. Hersteller, Bauherren, Planer und zuständige Behörden werden sich daher die Frage stellen, ob diese Produkte auf der Grundlage von Anhang 1 Nummer 2.1 Satz 7 Ziffer 1 der Deponieverordnung (DepV) im Deponiebau auch ohne Zulassung verwendet werden dürfen. Ein Vergleich der europäisch harmonisierten Bauproduktnormen DIN EN 13252 und DIN EN 13257, die der CE-Kennzeichnung der Geotextilien und geotextilverwandten Produkte zugrunde liegen, mit den Anforderungen der DepV zeigt nun aber, dass nur ein Teil der für den Deponiebau wesentlichen technischen Eigenschaften in diesen Normen erfasst werden. Daher sind für CE gekennzeichnete Produkte zusätzliche Prüfungen auf der Grundlage der DepV-Liste der Kriterien und Einwirkmechanismen erforderlich. Die in den Produktnormen beschriebene Qualitätssicherung ist nach Anhang 1 Nummer 2 Satz 14 ff der DepV ebenfalls für die Gleichwertigkeit nicht ausreichend. Eine CE-Kennzeichnung ist deshalb noch kein Nachweis, dass die Produkte dem Stand der Technik nach der DepV entsprechen und die Eigenschaften der Produkte den geforderten Eigenschaften im Wesentlichen gleichwertig sind, auch wenn mit Bezug auf den Anhang B der genannten Normen deren Dauerhaftigkeit für 100 Jahre vom Hersteller deklariert wird.----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
In the near future, CE-marked woven and nonwoven geotextiles, geocomposite drains and geogrids will be available on the market, whose declaration of performance will contain the qualification 'predicted service life up to 100 years' or even 'predicted service life minimum 100 years'. Manufacturer, principals and their design engineers as well as the responsible authorities will have to deal with the question, whether such products can be used on the basis of Annex 1, no. 2.1, sentence 7, cipher 1 of the German landfill ordinance (DepV) as components of landfill liner and capping systems. A comparison of the harmonized European standards hEN 13252 and 13257, on which the CE-marking of geotextiles and geotextile-related products is based, with the DepV, shows that only a few of the essential technical characteristics actually relevant for landfill constructions are considered in these standards. Therefore, additional tests based on the DepV-list of criteria and mechanisms of action are necessary for CE-marked products. Requirements on quality managements in the hEN are likewise not adequate for essential equivalence with respect to annex 1, No. 2.1, sentence 14 ff, DepV. Therefore, CE-marking is actually no proof of the fulfilment of the state of the techno logy according to the DepV and of the essential equivalence of product properties to the required properties, albeit the declaration of performance indicates a predicted service life of 100 years.