This Paper presents the results of a research programme conducted on the Cambridge University balanced-arm centrifuge, to study the long term transport of contaminants in the soil surrounding an engineered landfill site. The phenomena which govern the transport of hazardous waste through porous media are discussed, the principles of geo-technical centrifuge modelling are outlined, and relevant scaling laws that govern the relationship between the centrifuge model and its corresponding prototype, with respect to the problem of hazardous-waste transport, are presented. A centrifuge test, simulating two-dimensional migration of a conservative pollutant species from a landfill site, is described, and results from three such tests are presented. These results are compared with theoretical predictions from an existing one-dimensional transport code. L'article présente les résultats d'un programme de recherches effectuées sur la centrifugeuse a bras équilibré de l'Université de Cambridge pour étudier le transport à long terme des matières contaminantes dans le sol dans les environs des trachées construites pour les recevoir. Les phénomènes qui influencent le transport des déchets dangereux à travers les milieux poreux sont passés en revue et les principes de la modélisation des centrifuges géotechniques brièvement décrits. L'article présente aussi les lois d'échelle qui influencent les relations entre le modèle de la centrifugeuse et son prototype correspondant au problème du transport des déchets dangereux. Un essai à la centrifugeuse est décrit qui simule la migration bidimensionnelle d'une espèce de matière contaminante à toxicité de longue durée dans de telles tranchées. Les résultats de trois essais de ce type sont comparés avec des prédictions théoriques contenues dans un code de transport unidimensionnel déjà publié.

SUMMARYThis paper presents the results of a research programme conducted on the geotechnical centrifuge at The University of Western Australia to investigate coupled heat and contaminant transport in the soil surrounding a buried waste source. The phenomena which govern heat and contaminant transport through porous media are discussed, the principles of geotechnical centrifuge modelling are outlined, and relevant scaling laws that govern the relationship between a centrifuge model and the prototype, with respect to the problem of coupled waste transport, are presented. A model test, simulating two-dimensional migration from a buried heat and contaminant source, is described, and the results from four model tests are presented. The experimental data show that hydraulic instability is responsible for the transport of contaminant in the soil around the source and that the mode of instability is determined by the magnitude of the effective Rayleigh number.

SUMMARYWe derive a simple approximation for the steady-state distribution of solute subject to an arbitrary, irreversible transformation in a soil profile under the condition of steady fluid flow. The approximation accounts for the effect of dispersion in both the surface boundary Condition and the transport equation. The accuracy of the approximation is determined explicitly for the cases of zero-and first-order kinetics, where exact solutions are available. Data from a numerical scheme are used to check the approximation's accuracy for the widely used Michaelis-Menten kinetic rate. It is shown that existing approximations in which the effect of dispersion in the transport equation is ignored can affect significantly the value determined for the Michaelis-Menten saturation constant. Parameters found when the new method is applied to experimental data are found to agree closely with those estimated directly from a least-squares fitting.

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