117,711 research outputs found
Mechanics and velocity of large landslides
No full textLMSPreface of the special issue: Mechanics and velocity of large landslides. Guest Editors: C. Bonnard, L. Laloui, S. Scavia, M. Castelli. Special issue, Engineering Geology, Vol. 109, 2009
Elasto-plasticity of unsaturated soils : laboratory test results on a remoulded silt
No full textCurrent models of the elasto-plastic behaviour of unsaturated soils contain important underlying assumptions that have not been tested due to a lack of adequate experimental data. To address this issue, the objective of this paper is to provide a comprehensive set of experimental data An extensive experimental program has been performed on a remoulded unsaturated silt. To characterise its elasto-plastic behaviour, samples were taken through various stress paths, including wetting, drying and compression. Experimental results were analysed to provide (1) evidence of suction-induced preconsolidation; (2) dependence of cohesion and shear strength at failure on suction; (3) stiffness in relation to suction and (4) uniqueness of the critical state line.LMSModifications introduced by L. Laloui - Nov. 19, 200
Géostructures énergétiques
No full textLes géostructures énergétiques sont en pleine expansion dans le monde entier. Elles représentent une source d’énergie propre et renouvelable qui peut être utilisée pour le chauffage et la climatisation des bâtiments ainsi que pour le contrôle de la température des infrastructures. Cette technologie associe le rôle structurel des géostructures à l’approvisionnement énergétique, en utilisant le principe de la géothermie peu profonde. D’une part, en hiver, la chaleur est extraite du sol afin de satisfaire les besoins en chauffage et d’autre part, en été, la chaleur est injectée dans le sol afin de satisfaire les besoins en refroidissement. Le double rôle de ces structures rend leur conception particulièrement difficile et plus complexe que pour les projets plus conventionnels. Outre les procédures connues couramment appliquées à la mise en place d’une géostructure, plusieurs autres problèmes se posent lorsque l’on décide de l’exploiter du point de vue de l’approvisionnement d’énergie. Ces problèmes incluent notamment la conception et le dimensionnement de l’équipement géothermique, l’étude de la demande en énergie et l’optimisation du système qui en résulte, la considération des autres effets provoqués par la variation de température, sur la structure elle-même en termes de contraintes et de déplacements, et la définition des responsabilités des différents professionnels impliqués dans le projet. Comme les géostructures énergétiques constituent une nouvelle technologie en ingénierie, il est nécessaire d’approfondir les connaissances scientifiques à leur sujet et de définir des procédures de conception et de dimensionnement. Le but de cet ouvrage est de donner aux lecteurs une présentation exhaustive des connaissances possédées à ce jour concernant ces structures, et des procédures actuellement appliquées dans les régions où elles ont été mises en pratique. Ce livre est divisé en quatre parties, chacune étant composée de chapitres écrits par les meilleurs ingénieurs et chercheurs dans ce domaine. La première partie traite de la modélisation physique des géostructures énergétiques ; elle comprend des recherches en laboratoire sur le comportement thermomécanique des sols, des analyses in situ, des essais en centrifugeuse et des expériences à petite échelle. La deuxième partie comprend les résultats de simulations numériques de pieux énergétiques, de tunnels et de fondations de ponts, tout en examinant également la mise en pratique de telles structures dans différentes zones climatiques. La troisième partie traite des aspects pratiques d’ingénierie, depuis la mise en place des géostructures énergétiques jusqu’au développement d’outils de conception pour leur dimensionnement géotechnique. Enfin, cet ouvrage se conclut avec l’étude d’un cas réel.LM
Hydro-mechanical analysis of volcanic ash slopes during rainfall
No full textRainfall-induced landslides in volcanic ashes represent a major natural hazard in many regions around the world. Owing to their loose structure, volcanic ash slopes are prone to rainfall-induced landslides. The paper presents a continuum modelling approach for the analysis of wetting-induced instability phenomena at the onset of failure in loose volcanic ash slopes. A numerical simulation of a landslideprone volcanic slope in Costa Rica is carried out with a two-dimensional hydro-mechanical finiteelement slope model. A constitutive model based on the effective stress concept extended to partially saturated conditions is used to reproduce the volcanic ash hydro-mechanical behaviour. The model parameters were calibrated through a previous extensive laboratory testing campaign. Simulation results allow the behaviour of the slope during rainfall infiltration to be anticipated and the development of the failure mechanism to be analysed. Results of the coupled numerical model demonstrate the important role of wetting and drying cycles, slope geometry and bedrock on the timely evolution of matric suctions and wetting-induced deformations. Moreover, it is observed that the pore collapse upon wetting enhances the development of a localised shear failure mechanism in unsaturated conditions
Advances in the testing of the hydro-mechanical behaviour of shales
No full textThe paper presents some of the advanced experimental techniques and apparatuses that have been developed by the authors for testing the hydromechanical behaviour of shales. A methodology established for the analysis of the water retention behaviour in non-isochoric conditions is introduced; the method allows for the determination of the main drying and wetting paths in addition to the volume change response upon total suction variations. A high-pressure oedometric cell is then presented; the apparatus allows for the analysis of the transition from the pre-yield behaviour to the normally consolidated state. The analysis of the settlement versus time curves yields information on the permeability of the material as a function of the void ratio. The test results are illustrated for two Mesozoic shales from the northern region of Switzerland, namely, the Opalinus Clay from Mont Terri and the so called "Brown Dogger" from the Schlattingen site in the Molasse Basin. © Springer-Verlag Berlin Heidelberg 2013
Response of soils subjected to thermal cyclic loading: experimental and constitutive study
No full textThe response of soil subjected to thermal cyclic loading plays an important role in certain engineering applications, such as high-level nuclear waste disposal, heat storage systems, CO2 sequestration plant and energy geostructures. For instance, energy geostructures impose temperature variations that are daily and seasonally cyclic to the soil and might have consequences of engineering relevancy, mainly in terms of foundation displacements. This paper aims to experimentally investigate the response of a natural silty soil to thermal cyclic loading in drained conditions. The experimental program includes: (i) oedometric tests at various constant temperatures aimed at studying the sensibility of the material to temperature and (ii) thermal cyclic tests under constant vertical effective stress in oedometric conditions, with temperature ranging between 5 and 60 °C. As expected, the clay tested under Normal Consolidation conditions (NC) undergoes thermo-plasticity, and the results indicate that most of the irreversible deformation occurs during the first heating-cooling cycle, exhibiting an accommodative behaviour during the subsequent cycles. In other words, increments of irreversible deformation are observed in the thermal cycles successive to the first one, which generally become smaller and smaller cycle after cycle until stabilisation. In the end, the material tends to remain inside the elastic domain, exhibiting thermo-elastic expansion and contraction during heating and cooling. In the second part of the paper, an extension of an existing thermoelastic-thermoplastic constitutive model that aims to tackle the accommodative response is proposed. The extended model is able to reproduce the accommodation phenomenon thanks to an additional parameter called the cyclic plastic radius. The experimental results obtained are innovative in clarifying the response of soils subjected to drained thermal cyclic loading, and the constitutive model presented allows this aspect to be considered in the numerical analysis of the engineering applications where it is of concern.LM
Numerical analysis of the geotechnical behaviour of energy piles
No full textEnergy geostructures are rapidly gaining acceptance around the world; they represent a renewable and clean source of energy that can be used for the heating and cooling of buildings and for de-icing of infrastructures. This technology couples the structural role of geostructures with the energy supply, using the principle of shallow geothermal energy. The geothermal energy exploitation represents an additional thermal loading, seasonally cyclic, which is imposed on the soil and the structure itself. Because the primary role of the piles is the stability of the superstructure, this aspect needs to be ensured even in the presence of the additional thermal load. The goal of this paper is to numerically investigate the behaviour of energy pile foundations during heating–cooling cycles. For this purpose, the finite element method is used to simulate both a single and a group of energy piles. The piles are subjected to a constant mechanical load and a seasonally cyclic thermal load over several years, imposed in terms of injected–extracted thermal power. The soil and the pile–soil interface behaviours are reproduced using a thermoelastic-thermoplastic constitutive model. The thermal-induced stresses inside the piles and the additional displacements of the foundations are discussed. The group model is used to investigate the interactions between the piles during thermo-mechanical loading. The presented results are specific to the studied cases but lead to the conclusion that both the thermalinduced displacements and stresses, despite being acceptable under normal working conditions, deserve to be taken into account in the geotechnical design of energy piles.LM
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