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Hydromechanical behaviour of a heterogeneous compacted soil: experimental observations and modelling / A. Gens in Géotechnique, Vol. 61 N° 5 (Mai 2011) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 5 (Mai 2011) . - pp. 367–386 Titre : Hydromechanical behaviour of a heterogeneous compacted soil: experimental observations and modelling Type de document : texte imprimé Auteurs : A. Gens, Auteur ; B. Vallejan, Auteur ; M. Sanchez, Auteur Année de publication : 2011 Article en page(s) : pp. 367–386 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Laboratory  tests  Fabric/Structure  of  soils  Compaction  Partial  saturation  Expansive  soils  Full-scale  tests Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The paper describes a theoretical and experimental study of the coupled hydromechanical behaviour of a compacted mixture of bentonite powder and bentonite pellets intended as sealing material in underground repositories for nuclear waste. One of the main advantages of the use of powder/pellets mixtures is the reduction of the compaction effort required to achieve the value of average dry density necessary to attain the required swelling potential. However, the heterogeneous fabric of the material requires special approaches in order to describe adequately its behaviour during hydration. A double porosity formulation is presented to account for the presence of two distinct structural levels in the material. Hydraulic equilibrium between the two porosities is not assumed; instead a water exchange term between them is postulated. The formulation is applied to the modelling of a number of one-dimensional swelling pressure tests performed in the CEA (Commisariat à l'Énergie Atomique, France) and CIEMAT (Spain) laboratories. A very satisfactory quantitative description of the experimental observations is obtained that includes a number of complex behaviour features such as size effects and non-monotonic development of swelling pressures. Some microfabric observations using X-ray tomography and mercury intrusion porosimetry lend support to the conceptual approach adopted. The formulation is then applied to the analysis of a long-term large-scale sealing test performed at the Hades underground facility in Belgium, using the same set of hydraulic and mechanical parameters employed in the modelling of the laboratory tests. Although the field observations exhibit a much higher degree of scatter, the basic behaviour of the field sealing test is satisfactorily simulated. A formulation that incorporates basic features of the microfabric of the mixture is thus able to span successfully over a large range of space and time scales. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.sip11.p.015 [article] Hydromechanical behaviour of a heterogeneous compacted soil: experimental observations and modelling [texte imprimé] / A. Gens, Auteur ; B. Vallejan, Auteur ; M. Sanchez, Auteur . - 2011 . - pp. 367–386. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 5 (Mai 2011) . - pp. 367–386 Mots-clés : Laboratory  tests  Fabric/Structure  of  soils  Compaction  Partial  saturation  Expansive  soils  Full-scale  tests Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The paper describes a theoretical and experimental study of the coupled hydromechanical behaviour of a compacted mixture of bentonite powder and bentonite pellets intended as sealing material in underground repositories for nuclear waste. One of the main advantages of the use of powder/pellets mixtures is the reduction of the compaction effort required to achieve the value of average dry density necessary to attain the required swelling potential. However, the heterogeneous fabric of the material requires special approaches in order to describe adequately its behaviour during hydration. A double porosity formulation is presented to account for the presence of two distinct structural levels in the material. Hydraulic equilibrium between the two porosities is not assumed; instead a water exchange term between them is postulated. The formulation is applied to the modelling of a number of one-dimensional swelling pressure tests performed in the CEA (Commisariat à l'Énergie Atomique, France) and CIEMAT (Spain) laboratories. A very satisfactory quantitative description of the experimental observations is obtained that includes a number of complex behaviour features such as size effects and non-monotonic development of swelling pressures. Some microfabric observations using X-ray tomography and mercury intrusion porosimetry lend support to the conceptual approach adopted. The formulation is then applied to the analysis of a long-term large-scale sealing test performed at the Hades underground facility in Belgium, using the same set of hydraulic and mechanical parameters employed in the modelling of the laboratory tests. Although the field observations exhibit a much higher degree of scatter, the basic behaviour of the field sealing test is satisfactorily simulated. A formulation that incorporates basic features of the microfabric of the mixture is thus able to span successfully over a large range of space and time scales. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.sip11.p.015