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This paper describes the instrumentation, execution and performance of two full-scale tests where a braced steel sheet pile wall interacting with rows of overlapping dry deep mixing columns was excavated and then loaded to failure. The purpose of these tests was to provide knowledge of the behavior of deep mixing column rows located in the passive zone and interacting with a retaining structure. Both tests were extensively instrumented on the active as well as on the passive side of the retaining structure. In both conducted tests a stability failure of the retaining structure occurred, resulting in heave at the bottom of the excavation and large settlements of the ground surface behind the sheet pile wall. For a spacing between lime-cement (LC)-panels of 3.0 m, a very brittle failure developed suddenly in the clay between the panels with small deformations prior to failure. In the second test, with a spacing of 1.5 m between LC-panels, the failure developed in the LC-panels as well as in the clay between the panels. Even if a similar failure mechanism developed, measured horizontal displacements, horizontal stresses, and pore pressure response prior to failure differed between the tests. Key words: dry deep mixing, field test, excavation support, failure mechanism, pore pressure response. Ce document decrit l'instrumentation, l'execution et la performance de deux essais a grande echelle oU une paroi en palplanches en tole d'acier contreventee interagissant avec des rangees de colonnes de melange profondes seches chevauchees ont ete excavees, puis charge jusqu'a l'echec. Le but de ces essais etait de fournir des connaissances sur le comportement de rangees de colonnes a melange profondes situees dans la zone passive et en interaction avec une structure de retenue. Les deux tests ont ete abondamment instrumentees sur la matiere active, ainsi que sur la partie passive de la structure de retenue. Dans les deux essais effectues, un echec de la stabilite de la structure de retenue est produit, entrainant le soulevement du fond de l'excavation et de grands tassements de la surface du sol derriere le mur en palplanches. Pour un espacement entre les panneaux LC de 3,0 m, un echec tres fragile s'est developpe soudainement dans l'argile entre les panneaux avec de petites deformations avant l'echec. Dans le deuxieme essai, avec un espacement de 1,5 m entre les panneaux LC, l'echec s'est developpe dans les panneaux de chaux-ciment (LC), ainsi que dans l'argile entre les panneaux. Meme si un mecanisme de rupture similaire s'est developpe, mesure le long des deplacements horizontaux, des contraintes horizontales, la reponse de la pression interstitielle avant la rupture etait differente entre les essais. [Traduit par la Redaction] Mots-cles : melange a sec profond, essai sur le terrain, soutien d'excavation, mecanisme de rupture, reponse a la pression interstitielle., Introduction For excavations performed in soft clay deposits, large structural forces in the retaining structure as well as large ground displacements that could induce damage to surrounding structures can be [...]

For staging the construction of embankments on soft clay, an important aspect in deterministic or probabilistic stability analyses is the assessment of the representative average values and associated uncertainties for the undrained shear strength as the height of the embankment is sequentially increased. Assessments made prior to construction can be verified by performing observations during the construction phase. All relevant available information should be incorporated into an analysis to increase the level of confidence and the objectivity of the assessment. To this end, we apply an extended multivariate approach to assess the undrained shear strength using different indirect measurement methods during the staged construction of the Veda embankment (Sweden). This multivariate approach implies that uncertainties associated with the assessments are reduced, and objectively weighted averages are obtained. The resulting implications on the calculated deterministic safety factors and the probabilistically retrieved reliability indices of the embankment are thoroughly discussed in this work. Key words: statistical analysis, site investigation, shear strength, Bayesian statistics, multivariate analysis, probabilistic stability analysis. Lorsqu'on planifie la construction de talus sur des sols mous, un aspect important des analyses de stabilite deterministes ou probabilistes est revaluation des valeurs moyennes caracteristiques et des incertitudes correspondantes associees a la resistance au cisaillement non drainee a mesure que la hauteur du talus est augmentee de maniere sequentielle. Il est possible de verifier les evaluations realisees avant la construction en effectuant des observations durant la phase de construction. Il est necessaire d'incorporer toutes les informations pertinentes disponibles dans une analyse pour augmenter le niveau de fiabilite et l'objectivite de revaluation. Pource faire, nous utilisons une approche etendue a variables multiples pour evaluer la resistance au cisaillement non drainee a l'aide de differentes methodes de mesure indirectes durant la construction par etapes du talus ferroviaire de Veda (en Suede). Cette approche a variables multiples necessite de reduire des incertitudes associees aux evaluations et de determiner des moyennes objectivement ponderees. Les repercussions sur les facteurs de securite calcules et sur les indices de fiabilite obtenus de maniere probabiliste caracterisant le talus sont decrites en detail dans la presente etude. [Traduit par la Redaction] Mots-cles: analyse statistique, etude sur le terrain, resistance au cisaillement, statistique bayesienne, analyse a variables multiples, analyse de stabilite probabiliste., Introduction A reliable assessment of short-term (i.e., undrained or partially drained) stability is essential when designing and constructing a staged embankment on soft clay. The stability is highly dependent on [...]

Important features of the multivariate approach are discussed, and an extension to this approach is proposed whereby the total uncertainty in site investigation methods due to spatial averaging is assessed prior to its adoption. Results from a site investigation of spatially averaged values of undrained shear strength ([[bar.S].sub.u]) and the corresponding coefficient of variation ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) in Veda sulphide clay were used as a practical illustration of the extended multivariate approach and provide a basis for discussion. The inherent variability and scales of fluctuation for different methods are presented. The study shows the usefulness of the extended multivariate approach for the evaluation of representative values of [[bar.S].sub.u] and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] based on results from different methods. It is also a way of implicitly reducing the transformation errors that arise when a property is derived from measurement results. Nevertheless, considerable care must be taken as a much lower COV for one method will have a significant impact on the results. Key words: sulphide clay, undrained shear strength, embankments, statistical analysis, uncertainty, multivariate approach. Les caracteristiques importantes de l'approche multi-variable sont discutees, et une extension de cette approche est proposee. Dans cette extension, l'incertitude totale des methodes d'investigation de sites causee par l'estimation de la moyenne spatiale est evaluee avant d'etre adoptee. Les resultats de l'investigation de valeurs moyennes spatiales de la resistance au cisaillement non draine ([[bar.S].sub.u]) et du coefficient de variation ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) correspondant obtenues dans de l'argile sulfureuse de Veda ont ete utilises comme illustration pratique de l'approche multi-variable etendue, et sert de base de discussion. La variabilite inherente et les echelles de fluctuation des differentes methodes sont presentees. Cette etude demontre l'utilite de l'approche multi-variable etendue pour revaluation de valeurs representatives de [[bar.S].sub.u] et [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] base sur des resultats obtenus par differentes methodes. C'est aussi une fa^on implicite de reduire les erreurs de transformation qui apparaissent lorsqu'une propriete est derivee de resultats mesures. Neanmoins, il faut etre prudent puisqu'un COV nettement plus bas pour une methode aura un impact significatif sur les resultats. [Traduit par la Redaction] Mots-cles: argile sulfureuse, resistance au cisaillement non draine, digues, analyse statistique, incertitude, approche multi-variable., Introduction Robust and reliable assessment of uncertainties in soil engineering properties is one of the most important tasks in any geotechnical engineering project. One way of achieving this is to [...]