Search

In this paper, the behaviour of an idealized excavation carried out in a clay sensitive to destructuration is studied through a series of finite element analyses, employing an advanced bounding surface model developed for structured clays. Several cases are examined to investigate the influence of factors including the velocity of destructuration, damage to the soil-wall contact produced by the wall construction, and width-to-height ratio of the excavation. The case of a soil deposit insensitive to microstructural damage is also studied for comparison. Results of the numerical analyses show that the progressive dissipation of excess pore-water pressures generated during the excavation stage can damage the clay microstructure severely enough to trigger an instability phenomenon. If the clay structure deteriorates rapidly, the instability is concurrent with the dissipation of excess pore-water pressures. However, for a clay less sensitive to microstructural damage, the instability can occur towards the end of the consolidation process, or even be preceded by a deceptively stable time interval, during which small redistributions of pore-water pressure can trigger an important destructuration and collapse of the excavation. In a final part of the paper, results of the numerical analyses are used to provide indications about the most appropriate quantities to monitor to provide an effective early warning of the instability phenomenon. Key words: excavation, clays, consolidation. Dans cet article, le comportement d'une excavation idealisee realisee dans une argile sensible a la destructuration est etudie a travers une serie d'analyses en elements finis, en utilisant un modele de surface limite elabore developpe pour les argiles structurees. Plusieurs cas sont examines afin d'etudier l'influence de facteurs tels que la vitesse de destructuration, les dommages causes par la construction du mur au contact sol-mur, le rapport entre la largeur et la hauteur de l'excavation. Le cas d'un depot de sol insensible aux dommages de la microstructure est egalement etudie a des fins de comparaison. Les resultats des analyses numeriques montrent que la dissipation progressive des pressions interstitielles excessives generees au cours de la phase d'excavation peut endommager suffisamment la microstructure d'argile pour declencher un phenomene d'instabilite. Si la structure de l'argile se deteriore rapidement, l'instabilite est concomitante avec la dissipation des pressions excessives de l'eau dans les pores. Toutefois, pour une argile moins sensible aux dommages microstructuraux, l'instabilite peut survenir vers la fin du processus de consolidation, voire etre precedee d'un intervalle de temps trompeur, pendant lequel de petites redistributions de la pression interstitielle peuvent declencher une importante destructuration et un effondrement de l'excavation. Dans une derniere partie du document, les resultats des analyses numeriques sont utilises pour fournir des indications sur les quantites les plus appropriees a surveiller afin de fournir une alerte rapide et efficace du phenomene d'instabilite. [Traduit par la Redaction] Mots-cles : fouilles, argiles, consolidation., 1. Introduction The behaviour of excavations in fine-grained soils with low permeability is affected significantly by the drainage conditions. As an excavation causes a reduction of total mean stress in [...]

Copyright of Revue Française de Géotechnique is the property of EDP Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The seismic performance of integral abutment bridges (IABs) is affected by the interaction with the surrounding soil, and specifically by the development of interaction forces in the embankment‐abutment and soil‐piles systems. In principle, these effects could be evaluated by means of highly demanding numerical computations that, however, can be carried out only for detailed studies of specific cases. By contrast, a low‐demanding analysis method is needed for a design‐oriented assessment of the longitudinal seismic performance of IABs. To this purpose, the present paper describes a design technique in which the frequency‐ and amplitude‐dependency of the soil‐structure interaction is modelled in a simplified manner. Specifically, the method consists of a time‐domain analysis of a simplified soil‐bridge model, in which soil‐structure interaction is simulated by means of distributed nonlinear springs connecting a free‐field ground response analysis model to the structural system. The results of this simplified method are validated against the results of advanced numerical analyses, considering different seismic scenarios. In its present state of development, the proposed simplified nonlinear model can be used for an efficient evaluation of the longitudinal response of straight IABs and can constitute a starting point for a prospective generalisation to three‐dimensional response. [ABSTRACT FROM AUTHOR]

This paper discusses the implications of an approach to the limit states design of geotechnical structures in which the soil strength parameters are factored, as is the one contained in the European construction code. It is shown that a factored strength approach has very different implications for the two customary types of geotechnical analyses; namely, the study of plastic mechanisms and interaction analyses. The relationship between partial safety factors and the reliability of a system is highlighted first, with the aid of approximate reliability calculations relative to two example problems. It is then demonstrated that the method of factoring the soil strength may be regarded as an effective way to assess the distance of a structure from the activation of a plastic mechanism, and to relate this distance to a conventional measure of its reliability. Using the same examples, it is argued that the procedure of factoring the soil strength parameters is not appropriate for the evaluation of the internal forces in structural elements: most of the soil-structure interaction analyses are nonlinear and, at least partly, empirically based. The insertion of unrealistic parameters, such as the factored strength properties, in a complex calculation may produce ambiguous and uncontrollable results. Key words: limit states design, reliability, interaction analysis, strength factor, excavations. Cet article discute des implications de rutilisation de Tapproche de conception par etats limites pour des structures geotechniques dans lesquelles des facteurs des parametres de resistance des sols sont inclus, comme c'est le cas pour le code de construction europeen. L'article demontre que l'approche avec des facteurs de resistance a des implications tres differentes pour deux types d'analyse geotechnique usuelles, soil l'etude des mecanismes de plasticite et les analyses d'interaction. En premier lieu, la relation entre les facteurs de securite partiels et la fiabilite d'un systeme est presentee a partir de calculs approximatifs de fiabilite appliques a deux exemples. Il est ensuite demontre que Tapproche avec les facteurs de resistance des sols peut etre considered comme Line methode efficace pour evaluer la distance d'une structure par rapport a son point d'activation du mecanisme de plasticite. et peut etre utilises pour associer cette distance a une mesure conventionnelle de fiabilite. Les memes exemples ont ete utilises pour montrer que la procedure avec les facteurs des parametres de resistance des sols n'est pas appropriee dans le cas d'une evaluation des forces internes dans les elements stracturaux. En effet, comme la plupart des analyses d'interaction sol-structure sont non lineaires et, du moins en partie, basees sur des equations empiriques, l'ajout de parametres non realistes comme des facteurs des proprietes des sols dans des calculs complexes peut donner des resullals ambigus el non controlables. Mots-des : conception par etats limites, analyse d'interaction, facteur de resistance, excavations. [Traduit par la Redaction], Introduction Karl Terzaghi (1943) divided the problems of soil mechanics into two groups: 'stability problems' and 'elasticity problems.' in Terzaghi's words, stability problems 'deal with the conditions for the equilibrium [...]