Dépouillements

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

Modelling the response of Lechago earth and rockfill dam / E. E. Alonso in Géotechnique, Vol. 61 N° 5 (Mai 2011) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 5 (Mai 2011) . - pp. 387–407 Titre : Modelling the response of Lechago earth and rockfill dam Type de document : texte imprimé Auteurs : E. E. Alonso, Auteur ; S. Olivella, Auteur ; A. Soriano, Auteur Année de publication : 2011 Article en page(s) : pp. 387–407 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Field  instrumentation  Compaction  Numerical  modelling  Dams  Case  history Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Lechago dam (Teruel, Spain) is a 40 m high zoned earth and rockfill dam sitting on soft continental deltaic deposits. A relatively narrow central clay core is stabilised by wide rockfill shoulders. The dam was well instrumented and continuous records of stress development, pore-water pressures and vertical displacements are available for the construction period. Compaction conditions were followed by means of laboratory and in situ control tests. Core clay material was investigated by means of tests performed on compacted specimens of tertiary clays. Rockfill samples were excavated in outcrops of highly fractured Cambrian quartzitic shale. A testing programme on compacted rockfill gravels was conducted under relative humidity control in a large-diameter oedometer and triaxial cells. A coupled finite-element model has been developed to analyse the tests performed and dam behaviour during construction. Model predictions, essentially based on laboratory tests, are compared with measurements during construction. The predicted response of the dam under an assumed programme of impounding is also given. In the future, once impounding occurs, it will be possible to compare these predictions with actual dam performance. The paper provides an integrated description of the dam design, construction and early behaviour. It presents a procedure to interpret available data (laboratory as well as in situ data) on compacted materials from the perspective of modern constitutive models. It also provides an evaluation of the capabilities of advanced numerical tools to reproduce the measured dam behaviour. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.sip11.p.013 [article] Modelling the response of Lechago earth and rockfill dam [texte imprimé] / E. E. Alonso, Auteur ; S. Olivella, Auteur ; A. Soriano, Auteur . - 2011 . - pp. 387–407. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 5 (Mai 2011) . - pp. 387–407 Mots-clés : Field  instrumentation  Compaction  Numerical  modelling  Dams  Case  history Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Lechago dam (Teruel, Spain) is a 40 m high zoned earth and rockfill dam sitting on soft continental deltaic deposits. A relatively narrow central clay core is stabilised by wide rockfill shoulders. The dam was well instrumented and continuous records of stress development, pore-water pressures and vertical displacements are available for the construction period. Compaction conditions were followed by means of laboratory and in situ control tests. Core clay material was investigated by means of tests performed on compacted specimens of tertiary clays. Rockfill samples were excavated in outcrops of highly fractured Cambrian quartzitic shale. A testing programme on compacted rockfill gravels was conducted under relative humidity control in a large-diameter oedometer and triaxial cells. A coupled finite-element model has been developed to analyse the tests performed and dam behaviour during construction. Model predictions, essentially based on laboratory tests, are compared with measurements during construction. The predicted response of the dam under an assumed programme of impounding is also given. In the future, once impounding occurs, it will be possible to compare these predictions with actual dam performance. The paper provides an integrated description of the dam design, construction and early behaviour. It presents a procedure to interpret available data (laboratory as well as in situ data) on compacted materials from the perspective of modern constitutive models. It also provides an evaluation of the capabilities of advanced numerical tools to reproduce the measured dam behaviour. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.sip11.p.013

Physical modelling of wetting-induced collapse in enmbankment base / L. Thorel in Géotechnique, Vol. 61 N° 5 (Mai 2011) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 5 (Mai 2011) . - pp. 409-420 Titre : Physical modelling of wetting-induced collapse in enmbankment base Type de document : texte imprimé Auteurs : L. Thorel, Auteur ; V. Ferber, Auteur ; B. Caicedo, Auteur Année de publication : 2011 Article en page(s) : pp. 409-420 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Centrifuge  modelling  Collapsed  settlement  Compaction  Embankments  settlement Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The relevance of the oedometer tests used for the prediction of wetting-induced deformations in embankments is examined. Single and double oedometer tests are carried out. A comparison is made between laboratory tests and geotechnical centrifuge modelling at 100 g conducted to examine an inundated embankment made of a sand–clay mixture. A 20 cm high embankment model is built and instrumented. The material is compacted on the ‘dry side' of the optimum Proctor curve at a low compaction rate in order to emphasise settlement phenomena. The inundation simulation is conducted in two successive sequences during centrifuge flight up to a water table of 5 cm. The results prove that the prediction of the dry density after settlement due to inundation is good. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.10.p.029 [article] Physical modelling of wetting-induced collapse in enmbankment base [texte imprimé] / L. Thorel, Auteur ; V. Ferber, Auteur ; B. Caicedo, Auteur . - 2011 . - pp. 409-420. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 5 (Mai 2011) . - pp. 409-420 Mots-clés : Centrifuge  modelling  Collapsed  settlement  Compaction  Embankments  settlement Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The relevance of the oedometer tests used for the prediction of wetting-induced deformations in embankments is examined. Single and double oedometer tests are carried out. A comparison is made between laboratory tests and geotechnical centrifuge modelling at 100 g conducted to examine an inundated embankment made of a sand–clay mixture. A 20 cm high embankment model is built and instrumented. The material is compacted on the ‘dry side' of the optimum Proctor curve at a low compaction rate in order to emphasise settlement phenomena. The inundation simulation is conducted in two successive sequences during centrifuge flight up to a water table of 5 cm. The results prove that the prediction of the dry density after settlement due to inundation is good. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.10.p.029

Effects of the maximum soil aggregates size and cyclic wetting–drying on the stiffness of a lime-treated clayey soil / A. M. Tang in Géotechnique, Vol. 61 N° 5 (Mai 2011) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 5 (Mai 2011) . - pp. 421-429 Titre : Effects of the maximum soil aggregates size and cyclic wetting–drying on the stiffness of a lime-treated clayey soil Type de document : texte imprimé Auteurs : A. M. Tang, Auteur ; M. N. Vu, Auteur ; Y.-J. Cui, Auteur Année de publication : 2011 Article en page(s) : pp. 421-429 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Fabric/Structure  of  soil  Time  dependence  Suction  Soil  stabilisation  Laboratory  tests  Stiffness Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Lime treatment is a well-known technique to improve the mechanical response of clayey subgrades of road pavements or clayey soils used for embankment. Several studies show that lime treatment significantly modifies the physical and hydromechanical properties of compacted soils. Nevertheless, studies on the scale effect under climatic changes are scarce. Actually, wetting–drying cycles might significantly modify the microstructure of treated soils, giving rise to changes in hydromechanical properties. This modification could be dependent on the size of soil aggregates before lime treatment. In the present work, this scale effect was studied by investigating the stiffness of a compacted lime-treated clayey soil using bender elements. The studied soil was first air-dried and ground into a target maximum soil aggregates size (D max). For each aggregate size, the soil was humidified to reach the target water contents w i, then mixed with 3% of lime powder (mass of lime divided by mass of dried soil) prior to the static compaction at a dry density of 1·60 Mg/m3. Two initial water contents (w i = 14 and 18%) and four maximum soil aggregates sizes (D max = 0·4, 1·0, 2·0 and 5·0 mm) were considered. After the compaction, the soil specimen (50 mm in diameter and 50 mm high) was covered by plastic film in order to prevent soil moisture changes. The soil stiffness was then monitored at variable time intervals until reaching stabilisation. Afterwards, the soil specimen was subjected to full saturation followed by air-drying to come back to its initial water content. The results show that: (a) the soil stiffness after lime-treatment is significantly dependent on the aggregate size: the finer the aggregates the higher the soil stiffness; (b) the effect of initial water content on the stiffness is negligible; and (c) the wetting–drying cycles seem to slightly increase the soil stiffness in the case of lime-treated specimens and decrease the soil stiffness in the case of untreated specimens. Furthermore, when an intensive drying was applied reducing the soil water content lower than the initial level, the soil stiffness decreased drastically after the subsequent wetting. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.sip11.005 [article] Effects of the maximum soil aggregates size and cyclic wetting–drying on the stiffness of a lime-treated clayey soil [texte imprimé] / A. M. Tang, Auteur ; M. N. Vu, Auteur ; Y.-J. Cui, Auteur . - 2011 . - pp. 421-429. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 5 (Mai 2011) . - pp. 421-429 Mots-clés : Fabric/Structure  of  soil  Time  dependence  Suction  Soil  stabilisation  Laboratory  tests  Stiffness Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Lime treatment is a well-known technique to improve the mechanical response of clayey subgrades of road pavements or clayey soils used for embankment. Several studies show that lime treatment significantly modifies the physical and hydromechanical properties of compacted soils. Nevertheless, studies on the scale effect under climatic changes are scarce. Actually, wetting–drying cycles might significantly modify the microstructure of treated soils, giving rise to changes in hydromechanical properties. This modification could be dependent on the size of soil aggregates before lime treatment. In the present work, this scale effect was studied by investigating the stiffness of a compacted lime-treated clayey soil using bender elements. The studied soil was first air-dried and ground into a target maximum soil aggregates size (D max). For each aggregate size, the soil was humidified to reach the target water contents w i, then mixed with 3% of lime powder (mass of lime divided by mass of dried soil) prior to the static compaction at a dry density of 1·60 Mg/m3. Two initial water contents (w i = 14 and 18%) and four maximum soil aggregates sizes (D max = 0·4, 1·0, 2·0 and 5·0 mm) were considered. After the compaction, the soil specimen (50 mm in diameter and 50 mm high) was covered by plastic film in order to prevent soil moisture changes. The soil stiffness was then monitored at variable time intervals until reaching stabilisation. Afterwards, the soil specimen was subjected to full saturation followed by air-drying to come back to its initial water content. The results show that: (a) the soil stiffness after lime-treatment is significantly dependent on the aggregate size: the finer the aggregates the higher the soil stiffness; (b) the effect of initial water content on the stiffness is negligible; and (c) the wetting–drying cycles seem to slightly increase the soil stiffness in the case of lime-treated specimens and decrease the soil stiffness in the case of untreated specimens. Furthermore, when an intensive drying was applied reducing the soil water content lower than the initial level, the soil stiffness decreased drastically after the subsequent wetting. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.sip11.005

Some aspects of the behaviour of compacted soils along wetting paths / S. Taibi in Géotechnique, Vol. 61 N° 5 (Mai 2011) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 5 (Mai 2011) . - pp. 431–437 Titre : Some aspects of the behaviour of compacted soils along wetting paths Type de document : texte imprimé Auteurs : S. Taibi, Auteur ; J. M. Fleureau, Auteur ; N. Abou-Bekr, Auteur Année de publication : 2011 Article en page(s) : pp. 431–437 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Compaction  Clays Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Wetting and oedometric loading tests have been performed on several clayey compacted soils. The results highlight the influence of compaction water content and compaction stress on wetting paths. Comparing the changes in degree of saturation induced by mechanical loading and hydraulic loading (wetting path under null stress), it may be noticed that the oedometric path has an opposite curve of that of the wetting path, due to the fact that the void ratio decreases under constant water content when the stress is increased in one case (compression) and increases with water content in the other (swelling). DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.sip11.p.020 [article] Some aspects of the behaviour of compacted soils along wetting paths [texte imprimé] / S. Taibi, Auteur ; J. M. Fleureau, Auteur ; N. Abou-Bekr, Auteur . - 2011 . - pp. 431–437. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 5 (Mai 2011) . - pp. 431–437 Mots-clés : Compaction  Clays Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Wetting and oedometric loading tests have been performed on several clayey compacted soils. The results highlight the influence of compaction water content and compaction stress on wetting paths. Comparing the changes in degree of saturation induced by mechanical loading and hydraulic loading (wetting path under null stress), it may be noticed that the oedometric path has an opposite curve of that of the wetting path, due to the fact that the void ratio decreases under constant water content when the stress is increased in one case (compression) and increases with water content in the other (swelling). DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.sip11.p.020

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