Growing environmental awareness has led to developments within landfill engineering, increasing the amount of research with the aim of constructing safe, stable landfills with optimal geometry. EU member states are forced to improve waste disposal policies through directives (Council of the European Union 1999) enforced in member countries through local legislation (in the UK, The Landfill (England and Wales) Regulations 2002). This research focuses on several aspects of waste barrier in situ performance. A field study was conducted on a landfill side slope to investigate geosynthetics mechanical behaviour in service conditions and on a landfill capping to investigate capping geosynthetic drainage system performance in situ conditions and pore water distributions along the capping. Further site derived data were collected in order to validate numerical modelling approaches, to increase confidence in a design processes and to investigate mechanisms incorporated in the liner s performance. The side slope studies revealed an additional factor affecting lining components displacement along the slope: geomembrane and geotextile response to atmospheric conditions. The capping study allowed production of recommendations for future capping designs. These can be used to considerably enhance capping stability.

The main scope of this thesis is to select alternative landfill sites for Ankara based on the growing trends of Ankara towards the Sincan and G&ouml / lbaSi municipalities and to eventually select the best alternative. Landfill site selection was carried out utilizing Geographic Information System (GIS) and Multi-Criteria-Decision-Analysis (MCDA). A number of criteria were gathered in a GIS environment. Each criterion was assigned a weight value by applying the Pairwise Comparison Method (PCM). &ldquo / The Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS)&rdquo / , was applied and the best landfill site alternative was determined. The geotechnical properties of the clay samples, obtained from selected locations in G&ouml / lbaSi and Sincan were determined in order to design a landfill liner system using compacted &ldquo / Ankara Clay&rdquo / as the liner material. The permeability values for the clay samples were determined by performing falling head tests and consolidation tests. The coefficient of permeability value of the compacted clay was determined to be in the order of 10-10 m/s for the G&ouml / lbaSi samples and 10-11 m/s for the Sincan samples for both of the tests performed. These tests indicated that the native clay was suitable to be utilized as a landfill liner material. The HELP and POLLUTE was employed for the purpose of landfill design and predicting the landfill hydrological processes. The landfill profile with a double lining system composed of geomembrane/compacted clay composite top and bottom liners with a drainage layer was determined to show the best performance amongst the others.

Les géosynthétiques (GSY) sont des matériaux polymériques utilisés dans la construction d’ouvrages géotechniques et environnementaux, en remplacement et/ou en complément de matériaux naturels. Dans les installations de stockage de déchets non dangereux (ISDND), les GSY sont utilisés comme dispositif d’étanchéité et de drainage (barrière de sécurité) afin de prévenir les infiltrations de lixiviats vers la nappe phréatique.De nos jours, la rareté des sites adaptés à la construction de nouvelles ISDND conduit de nombreux opérateurs à opter pour la création de casiers de stockage en appui sur d’anciens casiers. Dans ces ouvrages en rehausse (extensions d’ISDND), une barrière de sécurité est généralement disposée entre les anciens casiers et les nouveaux casiers. Toutefois, dans cette configuration spécifique, les risques d’instabilité au glissement translationnel de l’ouvrage sont favorisés par la présence de plusieurs interfaces GSY représentant autant de surfaces de glissement préférentielles. Par ailleurs, ces risques sont accentués par le caractère compressible des déchets qui favorise l’apparition de tassements différentiels et/ou d’effondrements localisés (formation de cavités) sous la barrière de sécurité, susceptibles d’engendrer une perte d’intégrité (tensions / déformations excessives) de cette dernière. Dès lors, la compréhension des mécanismes associés à ces phénomènes de glissement translationnel et de déformation des GSY apparait capitale pour la réussite d’un tel projet.Dans ce contexte, les travaux objet du présent mémoire de thèse se sont attachés à mieux appréhender le comportement mécanique des systèmes GSY et de leurs interactions. Cette analyse a été effectuée sous l’angle de la stabilité au glissement translationnel (à l’échelle de l’ouvrage : grande échelle) et de l’intégrité structurelle des GSY au sein des barrières de sécurité sur cavité (petite échelle).Pour y parvenir, une analyse multi-approches associant étude analytique, modélisation numérique et étude expérimentale a été mise en oeuvre.Tout d’abord, le volet analytique a porté sur une analyse comparative de dix méthodes utilisées pour l’évaluation de la stabilité au glissement translationnel et de huit méthodes de dimensionnement des GSY de renforcement sur cavité. Ces études comparatives ont permis non seulement d’évaluer les écarts entre ces méthodes, mais aussi d’identifier celles qui se prêtent le mieux à une application en extension d’ISDND.Ensuite, une Méthode Rationnelle de Modélisation des systèmes Géosynthétiques (MeRaMoG) a été développée afin de prendre en compte fidèlement le comportement mécanique des GSY et de leurs interfaces (notamment la non-linéarité du comportement en traction des GSY). Grâce à la MeRaMoG qui a été validée expérimentalement, les mécanismes intervenant et contrôlant les phénomènes de glissement et de déformation des barrières de sécurité sur talus et sur cavité ont été investigués.Enfin, un Dispositif Expérimental grande-échelle pour l’étude de la Performance des GSY de renforcement sur Cavité (DEPGeC) a été développé. Le DEPGeC est un prototype permettant de simuler le comportement mécanique des GSY sur une cavité rectangulaire et sous une contrainte de confinement pouvant atteindre 100 kPa. L’utilisation du DEPGeC a permis d’évaluer l’influence de la contrainte de confinement, de la raideur du GSY de renforcement et d’un ancrage rigide sur les déformations des GSY. / Geosynthetics (GSYs) are polymeric materials that are used in engineering and environmental constructions to replace or in addition to natural materials. In landfills, GSYs are used as a lining system to prevent leachate infiltration into groundwater.Nowadays, the scarcity of suitable sites to establish new landfills leads more and more landfill owners to build new landfill cells over older ones. In such type of construction commonly called piggy-back landfill, a new GSY lining system is often implemented between old and new cells. However, in this specific configuration, the risk of translational instability of the construction is increased since the lining system involved several interfaces with low shear strength. Such instability is related to the failure of the various interfaces within the GSY lining system and hence to the sliding of GSY layers on each other. Moreover, the potential occurrence of differential settlements and / or localized collapses (cavity) which are related to the compressible nature of the waste within the old cell could tear (excessive tensile forces / strains) the GSY lining system under the overload of the new waste. Therefore, understanding the mechanisms controlling translational slip phenomena and deformation of GSYs is essential to ensure a proper design of such a project.In this context, this PhD thesis focused on better understanding of the mechanical behaviour of GSY systems and their interactions. The study was conducted using firstly a global analysis (large scale, all over the piggy-back landfill) of the lining system in terms of translational slips between the various GSYs. Secondly, this study investigated the integrity of the GSY lining system subjected to a cavity (small scale analysis).To achieve this goal, a multi-approaches investigation involving analytical study, numerical modelling and experimental study was performed.First, the analytical part focused on a comparative analysis based on ten methods used to assess the factor of safety of translational slip and on eight methods used for the design of GSY reinforcement over cavities. These comparative studies have not only assessed the differences between these methods, but also identified those best suited to be applied in the context of piggy-back landfills.Then, a rigorous method (MeRaMoG) that addressed the key aspects of the mechanical behaviour of GSYs and interfaces (e.g., the nonlinear axial stiffness of GSYs), was developed for the numerical modelling of multi-layered geosynthetic systems. Through MeRaMoG which was experimentally validated, the mechanisms controlling the translational slip and deformation of the geosynthetic lining system on side slopes and cavity were investigated.Finally, a new large-scale testing device (DEPGeC) was developed to assess the efficiency of a GSY reinforcement to bridge a cavity. The DEPGeC is a prototype that was used to simulate the mechanical behaviour of multi-layered GSY systems over a rectangular cavity and under a confining load of up to 100 kPa. Using the DEPGeC, the influence of the applied vertical load, the stiffness of the GSY reinforcement and a perfect anchorage on the deformations of GSY, was investigated.