Subsidence effects on clay barriers

Abstract

Centrifuge model tests have been performed to study the response of clay barriers subjected to differential deformations. The modes of deformation that have been observed are relevant to those that might occur as the result of differential settlements of waste material leading to deformation of cover liners, or from non-uniform soil strength profiles or the propagation of deep-sited subsidence towards the surface, leading to deformations of the base liner. Plane model liners were constructed both from pure kaolin and from a mixture of sand, silica flour and bentonite. The integrity and performance of these model liners were evaluated on a geotechnical centrifuge at 50 gravities. Physical degradation of the model liners was monitored photographically and their performance as effective hydraulic barriers assessed throughout the deformation process. For all the model liners where no overburden was present, tension cracking of the liner surfaces was observed. These tension cracks were very significant in the kaolin models and led to a drastic reduction in liner performance. However, the presence of an overburden suppressed the formation of tension cracks and no significant reduction in the kaolin liner efficiency was observed. The model liners fabricated from the sand, silica flour and bentonite mixture proved to be highly resistant to deformation with little evidence of tension cracking and no significant reduction in performance. Des essais à la centrifugeuse ont été effectuks sur des modéles afin d'étudier la réponse des écrans d'argile soumis á des déformations différentielles. Les modes de déformation sont coherents avec ceux qui pourraient se produire á la suite d' affaissements différentiels de déblais, conduisant á la déformation des écrans de couverture, ou comme résultat des profils de resistance non-uniformes des sols, ou de la propagation de l'effondrement depuis la base jusqu'au voisinage de la surface, conduisant à des déformations de l'écran de base. Des érans minces furent produits pour les maquettes avec du kaolin pur et d'un mélange de sable, de farine de silice et de bentonite. L'intérité et les performances de ces écrans modile furent évaluées sur un centrifuge à 50 gravites. La dégradation physique des écrans modéles fut enregistrée photographiquement et leurs performances comme barriéres effectives hydrauliques furent évaluées de facon continue pendant la déformation. Des fissures de traction furent observées dans tous les écrans modéles lá oú il n'y avait aucun terrain de couverture. Des fissures de tensions étaient trés importantes dans les modéles en kaolin et conduirent à une réduction drastique dans les performances des écrans. La présence d'un terrain de couverture supprima cependant la formation des fissures de traction et aucune réduction importante ne fut observée dans les performances des écrans en kaolin. Les écrans modéles fabriqués á partir de ce mélange de sable, de farine de silice et de bentonite se montrérent trés réistants á la déformation aver trés peu de fissures de traction et sans aucune réduction importante dans les performances.

Tension in geomembranes on landfill slopes under static and earthquake loading—Centrifuge study

“…Researchers in the past have used consolidated clay to model the compacted clay liners (Jessberger and Stone, 1991) and processed MSW to model the waste (Syllwasschy et al, 1996). The scaling laws of centrifuge modelling are given by Schofield (1980) and Taylor (1995).…”

Tensile behaviour of unsaturated compacted clay soils — A direct assessment method

“…The rapid, preferential transmission of water through the full depth of a crack (which can be on the order of metres) is potentially a significant mechanism for strength reduction in earthworks that could lead to earth structure failure. Tensile failure is also reported in clay barriers, where differential settlement of waste material causes cracking and a reduction in liner performance as an effective hydraulic barrier (Jessberger and Stone, 1991). Chemically modified/cement stabilised materials in road and rail line sub bases can also undergo tensile cracking induced by traffic generated cyclic stresses.…”

Influence of geomembrane on the deformation behaviour of clay-based landfill covers

“…The impervious barriers of landfill covers are more likely to be subjected to more mechanical damage compared to bottom lining systems since the former is subjected to lower overburden pressure. Excessive differential settlements can cause development of tension cracks in the clay barrier resulting in loss of integrity of whole cover system (Jessberger and Stone, 1991;Keck and Seitz, 2002;Dickinson and Brachman, 2006;Sharma and De, 2007;Heerten and Koerner, 2008).…”

“…Several studies reported that clay barriers lose the integrity at the onset of differential settlement (Jessberger and Stone, 1991;Scherbeck and Jessberger, 1993;LaGatta et al, 1997;Edelmann et al, 1999;Viswanadham and Mahesh, 2002;Rajesh and Viswanadham, 2011). But the studies pertaining to the deformation behaviour of composite barriers with a geomembrane overlying the compacted clay barrier subjected to differential settlements in a centrifuge is not yet reported to the best of authors' knowledge.…”