Movements Induced by Tunneling With an Epb Machine in over Consolidated Soils: Compans Monitoring Section of Toulouse Subway Line B

A part of Toulouse’s underground line B has been excavated by a 7.8 meters diameter earth-pressure balance machine. A comprehensive monitoring section has been installed in the Compans garden at a point where the tunnel cover is 12.8-meter and is running through overconsolidated clayey molasses underlying a 6.8 meters layer of made ground and gravels. The monitoring devices give full information on the ground movements above the tunnel and on deformations of the tunnel lining. Vertical movements are measured by 5 multipoint borehole extensometers with automatic data acquisition (every 5 seconds when the TBM crosses the monitoring section). At the end of each excavation phase, a high precision levelling of the borehole extensometer heads is performed in order to determine the total vertical displacements. Horizontal movements are measured by 3 inclinometers, one in the axis of the tunnel and the others on its sides, 2.3 meters away from the tunnel extrados. One of these inclinometers is 42 m long, i.e. 21.8 m below the level of the tunnel invert. The induced horizontal strains at ground level are measured by an invar thread in both longitudinal and transverse directions. Measurements show a specific behaviour of the soil due to its overconsolidated character (K0 greater than 1.5): even though the magnitude of the displacements is limited to a few millimeters, horizontal convergent movements are observed at the level of the tunnel axis while 3 to 4 times smaller heave is measured at ground surface (associated with horizontal extensions). Excavation parameters are automatically recorded and give information on the variation of the torque on the cutting wheel, the advancement rate, the confining pressure, the injection of annular void between soil and the concrete tunnel lining… This paper presents the results of the different monitoring devices and the possible correlations with the tunnel excavation parameters recorded by the TBM

MODELISATION NUMERIQUE DE L'INTERACTION SOL-STRUCTURE LORS DU PHENOMENE DE FONTIS

International audienceThis article focuses on the simulation of soil-structure interaction during a sinkhole development by the use of a coupling numerical modelling approach. The 2D model uses a Finite Difference computer code associated with a Distinct Elements code to optimize the performances of both softwares. This allows an important decrease of computation time and the results computed are close of the experimental observations made before

Apport de la modélisation expérimentale et numérique à la compréhension du phénomène d'interaction et numérique sol-structure lors d'un fontis

International audienceThis article is focused on the study of soil-structure interaction during the occurrence of a sinkhole by the use of a small-scale experimental model and a coupled numerical approach. The experimental model uses a 2D analogical soil and a building model. Tests in greenfield conditions and with the building allow determining the soil-structure interaction phenomenon. Computer simulations are validated with the results from the ex-perimental tests in order to run parametrical studies in a further developmentCet article présente une étude de l'interaction sol-structure durant la formation d'un fontis à l'aide d'un modèle physique puis d'une modélisation numérique couplée. Le modèle réduit expérimental utilise un matériau ana-logique bidimensionnel et une maquette de structure. Des essais en terrain vierge puis en présence de la structure permettent de caractériser la nature de l'interaction sol-structure. Les simulations numériques sont validées sur les résultats des essais expérimentaux en vue de mener des études paramétriques ultérieure

Understanding Sinkhole Consequences on Masonry Structures Using Large Small-Scale Physical Modeling

Subsidence and sinkhole are one of important geological risk due to the collapse of underground cavities either natural cavities or due to the human activities (such as mines). The impact of the subsidence and sinkhole on the existing structures can be sever and dramatic. The prediction of the level of damage depends on the characteristics of the sinkhole and the characteristics of the structures. A large small-scale physical model is developed by the INERIS in order to improve the understanding of the behavior of individual masonry structures subjected to ground subsidence or the collapse of underground cavities. The masonry structure is simulated by using small pieces of wood or sugar pieces, the foundations by polycarbonate or silicon slab. The displacements and strains of the soil and the structure are measured using an imagery technique called DIC (Digital Image Correlation). The results highlighted the influence of the soil-structure interaction on the subsidence. The silicon slab is less stiff allowing more displacement transfer to the structure. The experimental study pointed out the advantages of using wood and sugar material to represent a masonry structure, the using of sugar and wood is easy to deal and economic compared to real large scale test. The study showed that the damage of the masonry structure depends on its position on the subsidence area and it’s stiffness. The experimental analysis has pointed out the importance of the soil/structure interaction

Collapses of underground cavities and soil-structure interactions : experimental and numerical models

International audienceThe great subsidences result from the collapses of underground cavities man-made (mines or careers) or formed naturally by water flow in soluble solid masses of rocks (limestone, gypsum). Their impact on the existing structures standing on the surface is generally very important as show the recent examples of Auboué (1996), Moutiers (1997) and Roncourt (1999) which damaged more than five hundred buildings and the sinkhole on building site of METEOR subway in 2003. It is thus necessary to forecast the movements of the soil surface (subsidence and horizontal deformation) resulting from these phenomena and especially to determine the impact that may have the presence of structures on the form and the amplitude of these movements. The current practice to forecast the effects on the structures consists in determining the movements caused by the subsidence of the cavity without the building (in greenfield) then to use these results to check the capacity of the structure to resist the phenomenon. This approach can largely underestimate or over-estimate the generated loading, which in both cases has negative impacts (risk remaining for the structure or overcost of project in the other hand). In the present communication, soil-structure interaction during a sinkhole phenomenon is studied by a dual approach using a physical model and a numerical method. First of all, the physical model will use the bidimensionnal Schneebeli material in a small-scale model allowing fully controlled tests. The Schneebeli material is modified in order to allow the presence of cohesion. The soil mass of great dimensions (2m width for 1m height) makes it possible to represent the happening of a sinkhole with a scale factor of 1/40. The use of a building model will allow us to shed some light on the soil-structure interaction during the sinkhole. Thereafter we will set a numerical model using a coupled approach betwen finite difference and discrete element (FLAC2D – PFC2D coupled computations). This will allow us to study more easier different case of parameters : the size of the cavity, the thickness of the roof over the cavity, the position of the structure compared to the cavity, etc ..

Efficiency of mitigation measures for structures subjected to ground movement

International audienceSurface subsidence resulting from the collapse of underground cavities, whether natural or man-made can interact with existing buildings on the surface. One of the mitigation measures used is to dig a peripheral trench at a certain distance from the structure, filled with a soft material, like peat, or artificial material. This is thought to reduce the horizontal strain applied to the structure. The 3D numerical analysis presented in this paper is a first step towards evaluating the efficiency of this type of mitigation technique. The numerical model developed using Abaqus allows the effect of various parameters such as the width or depth of the peripheral trench, its distance from the building and/or the stiffness and strength of the filling material to be clearly determined

A New International Database on Case Histories of Monitored Construction of Tunnels and Deep Excavations

The prototype of a new database for case histories of monitored construction of tunnels and deep excavations is presented in this paper. The basic requirements for this database have been established by the members of the Technical Committee TC28 of the International Society for Soil Mechanics and Geotechnical Engineering. It is based on the Content Management System (CMS) Typo3. The resulting structure is flexible, the data being mirrored on sites managed by each participant providing data. It uses a web interface where the user can navigate and access to the data via an indexed search engine. Some very basic and brief standard forms describe the type of work, the geotechnical context and the data available. The monitoring data are organized according to formats chosen by each of the participants. Guidelines and minimal rules have also been proposed in order to ensure that the data can be actually used. Nevertheless, the rules concerning availability/accessibility of the data outside the TC28 partners involved in the creation of the database still need to be discusse

Large-scale soil-structure physical model (1g) - assessment of structure damages

International audienceThe paper presents a new large small-scale physical model (6 m3) for studying the damage to structures owing to underground movements: settlement, subsidence and sinkhole. The aim of the research is to study the soil-structure interaction effect of large vertical displacement owing to underground mines. The soil used in the physical model is Fontainebleau sand. The simple masonry structure was built using different materials: polycarbonate, silicone, wood and sugar. The vertical displacement was applied by an electric jack. The physical model is used to reproduce ground surface displacement profiles and the displacement measurement system is based on digital image correlation. Image processing was carried out to analyse the soil and structure displacements. The model allowed comparing the behaviour of soil and structure under different conditions: greenfield and with structure (different positions). Tension cracks appear when the applied subsidence reaches the structure's bearing capacity. The structure damage (cracks) depends on the structure position and the transfer of soil movement to the structure. These results also highlight the importance of the structure position in the development of cracks and damage to the masonry structure. The physical model presents an excellent tool for understanding the behaviour of real buildings and facilities

Tunnels en milieu urbain (Prévisions des tassements avec prise en compte des effets des pré-soutènements (renforcement du front de taille et voûte-parapluie))

Dans les années 80, de nouvelles techniques, basées sur la mise en place de système de présoutènements à l avant du front de taille, se sont développées dans le domaine du creusement de tunnels dans des terrains difficiles. Ce travail de thèse représente une contribution à l étude des effets de deux types de présoutènements mis en œuvre, le boulonnage au front et la voûte parapluie, sur les déformations du massif et sur la valeur du taux de déconfinement. L objectif étant d améliorer les méthodes de prévision des tassements en surface pour les tunnels réalisés avec des techniques de présoutènements. Pour atteindre ce but, l étude s est basée sur deux étapes principales : dans un premier temps, une participation active au suivi régulier des déformations enregistrées sur le chantier du tube sud de Toulon ; dans un deuxième temps, l élaboration d analyses en retour à l aide de modélisations numériques calées sur les observations collectées sur le chantier. Le suivi des déformations du massif et la mise en place de deux sections ins-trumentées ont permis d acquérir une importante base de données sur laquelle les simulations numériques ont été validées. Les mesures enregistrées in situ ont mis en évidence que le champ de déformation provoqué par le creusement du tunnel est tridimensionnel. L analyse de l évolution des mouvements en surface a également conduit à proposer une expression analytique de prévision des tassements de surface, qui a été ensuite utilisée pour le pilotage du creusement du tunnel. Des analyses en retour, basées sur les mesures enregistrées in situ, ont été réalisées avec des simulations numériques bidimensionnelles et tridimensionnelles. L approche 2D a souligné la forte influence du choix de la valeur du taux de déconfinement sur les résultats numériques. Afin de lever cette incertitude, un modèle 3D a été mis au point et a permis d étudier l influence des différents systèmes de (pré)soutènements sur la réaction du massif encaissant. Le boulonnage au front de taille et la distance de retard du contreradier ont montré avoir un rôle prépondérant sur le développement des mouvements dans le massif. Des calculs bidimensionnels ont été effectués en parallèle et les résultats ont été calés sur ceux du calcul 3D afin de trouver le taux de déconfinement correspondant à chaque configuration de (pré)soutènement testée. Les deux approches numériques, 2D et 3D, ont enfin été calées sur une section du tunnel de Toulon et la correspondance très satisfaisante avec les mesures in situ a permis de valider nos simulations. Une réflexion finale sur les résultats obtenus semble montrer que le taux de décon-finement est beaucoup plus influencé par le phasage des travaux et le présoutènement, que par les caractéristiques géomécaniques intrinsèques du massif.During the 80s, new technologies, based on face reinforcement systems, were developed in the field of tunnels excavation in complex soils. The following thesis is a further contribution to the analysis on the effects of two types of pre-reinforcements, tunnel face bolting and pipe umbrella, in the massif deformations and in the stress release value. The aim being to improve methodologies of surface settlements prevision for tunnels built through pre-reinforcement techniques, this study has been divided into two main steps. At first, deformations monitoring registered on site during the Toulon south tube excavation has been actively followed. Secondly, back analysis based on ob-servations collected on site has been elaborated using numerical modelling. The numerical simulations have been validated thanks to an important database obtained by deformations monitoring and by setting up two instrumental sections. Measures registered on site have shown that the deformation field caused by tunnel excavation is tridimensional. Furthermore, analysis on surface movement evolution has led to an analytical expression for surface settlements predictions, which has been used for tunnelling process adaptation. Afterwards, back analyses based on measures registered on site have been realised using bi-dimensional and tri-dimensional numerical simulations. The 2D approach stressed out the strong impact of the stress release value on numerical results. For this reason, a 3D model has been built and eventually used to study reinforcement systems influence on the ground mass reaction. Tunnel face bolting and tunnel invert position have shown to be of huge importance for the ground movements development. At the same time, bi-dimentional calculations have been made and results have been fitted on 3D calculation ones. This operation has permitted to find the stress release value corresponding to each pre-reinforcement configuration tested before. Finally, both 2D and 3D numerical approaches have been fitted on one area of Toulon tunnel and the satisfactory matching with measures taken on site has validated our simulations. In conclusion, one further analysis on results seems to show that stress release value is much more influenced by workflow steps and pre- reinforcement than by ground geomechanical characteristics.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocVILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

Evaluation de la dégradation du ballast ferroviaire à partir des simulations par éléments discrets des conditions de voie et de l'essai Micro-Deval

En raison de la circulation des trains et des opérations de maintenance (bourrage), les grains de ballast ferroviaire s'usent. Cela entraine une perte graduelle de performance qui nécessite finalement le renouvellement de l'ensemble du ballast. Afin de prédire l'évolution de cette dégradation, une étude multi-échelle est proposée. Des simulations par éléments discrets de l'essai d'attrition Micro-Deval permettent relier le chargement microscopique à la production de particules fines observée expérimentalement. La même approche numérique est utilisée avec des simulations du trafic des trains et de l'opération de bourrage pour déterminer les chargements microscopiques caractéristiques avec les conditions de voie