This lecture describes the latest findings with respect to the long-term performance of modern municipal solid waste (MSW) landfill barrier systems. Field data relating to the clogging of leachate collection systems and the latest techniques for predicting their performance are examined. It is indicated that the primary leachate collection systems may have service lives that range from less than a decade to more than a century, depending on the design details, waste characteristics and mode of operation. Recent data indicate that landfill liner temperatures can be expected to reach at least 30–40°C for normal landfill operations. With recirculation of leachate the liner temperature increases faster than under normal operating conditions, and may be expected to exceed 40°C. Temperatures (up to 40–60°C) may occur at the base of landfills where there is a significant leachate mound. Temperature is shown to have a significant impact on both contaminant migration and the service life of the liner system. Field measurements and theoretical calculations show that composite liners are substantially better than single liners in terms of controlling leakage from landfills. Also, the leakage rates with a composite liner are very small, and diffusion will dominate as a transport mechanism for contaminants that can readily diffuse through a geomembrane (GM). Composite liners involving a GM over a geosynthetic clay liner (GCL) gave rise to substantially less leakage than those involving a compacted clay liner (CCL). The observed leakage through composite liners can be explained by the holes in, or adjacent to, wrinkles/waves in the GM, and this leakage can be calculated using simple equations. High-density polyethylene (HDPE) GMs provide an excellent diffusive barrier to ions. However, some organic compounds readily diffuse through HDPE GMs, and a combination of GM and an adequate thickness of liner and attenuation layer are required to control impact to negligible levels. The long-term performance of HDPE GMs is discussed. Based on the currently available data, the service life for HDPE GM in MSW landfill is estimated to be about 160 years for a primary liner at 35°C and greater than 600 years for a secondary GM provided it is at a temperature of less than 20°C. Clay liners are susceptible to both shrinkage and cracking during construction (due to heating by solar radiation or freezing) and after placement of the waste (due to temperature gradients generated by the waste). The former can be controlled by quickly covering the liner with a suitable protection layer. The latter can be controlled by appropriate design. The use of numerical models for predicting the service lives of engineered systems and long-term contaminant transport is demonstrated.

This Paper describes a theoretical investigation into the behaviour of anchor plates in sand. Consideration is given to the effects of anchor embedment, friction angle, dilatancy, initial stress state K⁰ and anchor roughness for anchor plates with either a vertical or a horizontal axis. Collapse loads are observed to increase sensibly with embedment. Deep anchors exhibited high collapse loads. However, because of local yield, the deformations of deep anchors before collapse may be sufficiently large to necessitate the adoption of a practical definition of failure at loads below the actual collapse load. Soil dilatancy and anchor roughness significantly affect anchor capacity for certain cases, but the effect of K₀ on collapse load is small for typical cases. The theoretical results are compared with the results of the Authors' model tests as well as other model and field test data. There is encouraging agreement and, for the cases considered, the theoretical results provide a reasonable prediction of anchor capacity. The theoretical results for sand are extended to the case of cohesive–frictional soils. The theoretical results are presented in influence charts which may be used in hand calculations to obtain an estimate of anchor capacity for a wide range of geometries and soil types. The use of these charts is illustrated by a worked example. L'article décrit une recherche théorique sur le comportement des plaques d'ancrage dans le sable, en fonction de l'encastrement de l'ancrage, de l'angle de frittement, de la dilatance, de l'état de contrainte initiale K₀ et de la rugosité des plaques d'ancrage à axe vertical ou horizontal. On a constaté que la charge de rupture s'accroît sensiblement avec l'encastrement de l'ancrage et que des ancrages profonds fournissent de grandes charges de rupture. Cependant à cause de fluage local les déformations des ancrages profonds avant rupture peuvent être assez grandes pour nécessiter l'adoption d'une definition pratique de la rupture à des charges audessous de la charge de rupture réelle. La dilatance du sol et la rugosité de l'ancrage affectent la charge utile de l'ancrage d'une façon significative dans de certains cas, mais l'effet de la valeur K₀ sur la charge de rupture est faible dans les cas typiques. Les résultats théoriques sont comparés aux résultats des tests-modèles de l'auteur aussi bien qu'avec d'autres données modéles et pratiques. On trouve une correspondance encourageante et les résultats théoriques fournissent une prévision raisonnable de la charge utile dans les cas considerérés. Les résultats théoriques obtenus pour le sable sont étendus au cas des sols cohérents. Les résultats théoriques sont présentés sous la forme d'abaques d'influence qui peuvent être employés dans des calculs manuels pour obtenir une évaluation approximative de la charge utile pour une large gamme de géométries et de types de sol. L'emploi de ces abaques est illustré a l'aide d'un exemple.

A simple, numerically based procedure for the estimation of the so-called gap parameter is described. The gap parameter represents the vertical displacement above the crown of the tunnel and is a measure of ground loss owing to tunnelling in soft ground. This parameter is a function of the three-dimensional elastoplastic deformation at the tunnel face, the tunnelling machine shield and lining geometry, and workmanship. This parameter can then be used to predict the resulting ground deformations using either two-dimensional finite element methods or empirical correlations. Key words : tunnelling, settlement, subsidence, clays, soft ground, analysis, design.

The factors that may affect short-term leakage through composite liners are examined. It is shown that the leakage through composite liners is only a very small fraction of that expected for either a geomembrane (GM) or clay liner (CL) alone. However, the calculated leakage through holes in a GM in direct contact with a clay liner is typically substantially smaller than that actually observed in the field. It is shown that calculated leakage taking account of typical connected wrinkle lengths observed in the field explains the observed field leakage through composite liners. Provided that care is taken to avoid excessive connected wrinkle lengths, the leakage through composite liners is very small compared to a typical GM or CL alone. It is shown that the leakage through composite liners with a geosynthetic clay liner (GCL) is typically much less than for composite liners with a compacted clay liner (CCL). Finally, factors that will affect long-term leakage through composite liners are discussed. It is concluded that composite liners have performed extremely well in field applications for a couple of decades and that recent research both helps understand why they have worked so well and provides new insight into issues that need to be considered to ensure excellent long-term liner performance of composite liners — especially for applications where the liner temperature can exceed about 35 °C.

The undrained behaviour of anchor plates with a vertical or horizontal axis, resting in a saturated clay, is examined. Theoretical consideration is given to the effects of anchor embedment, layer depth, overburden pressure and breakaway condition as well as anchor roughness, thickness and shape. The influence of these parameters on the failure mechanism and the anchor capacity is discussed. It is shown that in many cases ultimate collapse is preceded by significant anchor displacement and a definition of failure which allows reasonable displacement predictions to be made at working loads is proposed. Model tests for anchors with a vertical axis are reported. A comparison of these results and other published data with the theoretical solutions indicates encouraging agreement. The results of this study are presented in the form of charts which may be used directly in hand calculations for estimating the undrained failure load for anchor plates. L'article décrit le comportement non-drainé des plaques d'ancrage à axe vertical ou horizontal qui reposent dans l'argile saturée et décrit du point de vue théorique les effets de l'encastrement de l'ancrage, de la profondeur des couches, de la pression du terrain de couverture de la rugosité de l'épaisseur et de la forme de l'ancrage. L'influence exercée par ces paramètres sur le mécanisme de rupture et la charge utile de l'ancrage sont aussi discutées. On démontre que dans beaucoup de cas la rupture finale est précédée d'un déplacement significatif de l'ancrage et on propose une définition de la rupture qui facilitera la prévision raisonnable des déplacements sous charges de service. Un compte-rendu est donné de tests-modèles pour les ancrages à axe vertical. Une comparaison de ces résultats et d'autres données déjà publiées avec les solutions théoriques indique une correspondance encourageante. Les résultats de cette étude sont présentés sous la forme d'abaques qui peuvent être employés de façon directe dans des calculs manuels pour évaluer la charge de rupture des plaques d'ancragé dans des conditions.