Daniel Dias | Joseph Fourier University (original) (raw)

Papers by Daniel Dias

Revue Française de Géotechnique, 2007

This paper proposes a three-dimensional numerical modelling of an embankment over soft soil impro... more This paper proposes a three-dimensional numerical modelling of an embankment over soft soil improved using vertical rigid piles. Arching occurs in the embankment fill, leading to partial load transfer onto the piles as well as surface settlement reduction and homogenisation. The piles, the soft soil and the embankment are simulated within a continuum m odel. A representative unit cell from the pile grid is first taken into account, then a current embankment section is simulated, in order to highlight the fully three-dimensional behaviour of this type of structure. The last part compares numerical results to design m ethods.

Earthquakes and Structures, 2019

Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2020

Disclaimer The AM is yet to be copyedited and formatted in journal house style but can still be r... more Disclaimer The AM is yet to be copyedited and formatted in journal house style but can still be read and referenced by quoting its unique reference number, the digital object identifier (DOI). Once the AM has been typeset, an 'uncorrected proof' PDF will replace the 'accepted manuscript' PDF. These formatted articles may still be corrected by the authors. During the Production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal relate to these versions also. Version of record The final edited article will be published in PDF and HTML and will contain all author corrections and is considered the version of record. Authors wishing to reference an article published Ahead of Print should quote its DOI. When an issue becomes available, queuing Ahead of Print articles will move to that issue's Table of Contents. When the article is published in a journal issue, the full reference should be cited in addition to the DOI.

Proceedings of the 5th International Symposium TC28. Amsterdam, the Netherlands, 15-17 June 2005, 2006

Tunnelling and Underground Space Technology, 2015

This paper aims at presenting a three-dimensional (3D) failure mechanism for a circular tunnel dr... more This paper aims at presenting a three-dimensional (3D) failure mechanism for a circular tunnel driven under a compressed air shield in the case of a dry multilayered purely frictional soil. This mechanism is an extension of the limit analysis rotational failure mechanism developed by Mollon et al. (2011a) in the case of a single frictional layer. The results of the present mechanism are compared (in terms of the critical collapse pressure and the corresponding shape of the collapse mechanism) with those of a numerical model based on Midas-GTS software. Both models were found to be in good agreement. Furthermore, the proposed mechanism has the significant advantage of reduced computation time when compared to the numerical model. Thus, it can be used in practice (for preliminary design studies) in the case of a multilayered soil medium.

Revue Française de Génie Civil, 2002

Le dimensionnement des structures souterraines renforcées nécessite une connaissance approfondie ... more Le dimensionnement des structures souterraines renforcées nécessite une connaissance approfondie du comportement du sol, des boulons et de l'interface sol/boulons. Afin de déterminer la loi de frottement d'interface, des essais de traction in-situ ont été réalisés sur des boulons radiaux scellés équipés de jauges de déformation. La méthode analytique développée par [BOUR 94] permet de déterminer les paramètres de la loi locale de frottement, supposée identique sur toute la longueur du boulon, à partir de la relation globale qui relie la force au déplacement de la tête de l'inclusion et des mesures extensométriques locales. Cette loi d'interaction sol/boulon a ensuite été implémentée dans un modèle numérique tridimensionnel de tunnel à front renforcé par boulonnage. Afin d'évaluer l'incidence de la loi d'interaction sol/boulon en termes de déplacements du front et d'effort dans le boulonnage, nous présentons une étude paramétrique faisant intervenir plusieurs types de lois de frottement. ABSTRACT. The design of reinforced structures requires a perfect knowledge of the behaviour of the soil, the bolts and of the soil/bolt interface. To determine the frictional law between the soil and the bolt, full-scale pullout tests were performed on radial anchor bolts, equipped with strain gauges. The analytical method developed by [BOUR 94] allows to derive the local frictional law parameters (assumed constant along the rod) from the global relationship between the total load and the head displacement. This frictional law is introduced in a 3D tunnel model with reinforced face. The 3D numerical model provides an accurate geometrical description of the tunnel structure, such as the lining behind the face, as well as the interface law between bolts and ground. To observe the influence of the soil/bolt interface, we study the influence of several frictional laws in terms of face displacements and axial forces in the bolts.

Canadian Geotechnical Journal, 2015

This paper describes a case history of a pile-supported industrial structure with an area improve... more This paper describes a case history of a pile-supported industrial structure with an area improvement ratio of 2.2%. Field-monitored data from the contact pressures acting on the pile, the mattress, and underneath the concrete slab; pore-water pressures; settlements; and vertical strains in the inclusions are reported and discussed. The case history is back-analyzed by performing a three-dimensional (3D) finite difference analysis. The measured and computed results are compared and discussed. Based on the field observations of the contact stresses and pore-water pressures and the numerical simulations of the industrial structure construction, it is clear that there was a load transfer from the soil to the piles due to soil arching. The measured contact pressure acting on the pile was approximately six times higher than that acting on the soil located between the piles. Numerical predictions of the stress reduction, differential settlement, and pile strain are consistent with the mea...

ABSTRACT RÉSUMÉ — Une technique de renforcement des sols compressibles consiste à mettre en place... more ABSTRACT RÉSUMÉ — Une technique de renforcement des sols compressibles consiste à mettre en place un réseau d'inclusions rigides dans le sol, surmonté d'une plate-forme granulaire de transfert de charge. La plateforme est renforcée à sa base par un géosynthétique. Cette technique est étudiée au travers d'une modélisation numérique par la méthode des éléments finis. Ce modèle numérique, axisymétrique, est calibré à partir d'essais menés en centrifugeuse sur un modèle réduit, le plateau mobile. Il consiste à simuler le tassement d'un sol compressible par la descente verticale d'un plateau autour d'un réseau de cylindres fixés sur une plaque. La mise en tension du géosynthétique et les frottements inter-granulaires transfèrent tout ou partie des charges vers les inclusions. La hauteur du matelas et l'espacement entre les inclusions du modèle varient au cours d'une série d'essais. ABSTRACT — A soft soil reinforcement technique consists in putting a network of rigid inclusions into the ground. Above the reinforced soft soil is installed a granular load transfer platform. This platform is reinforced at its bottom by a geosynthetic. This technique is studied using a numerical model, calibrated thanks to tests on a centrifuged small scale device (the mobile tray). It consists in simulating the settlement of a soft soil by prescribing to a tray a downward displacement. The tray slides around a network of cylindrical inclusions. The tensioning and the friction inter-grain transfer a part of the loads towards the inclusions. A parametric study is performed on the mattress thickness and the pile spacing.

O presente artigo aborda uma nova aplicação do método observacional na engenharia de túneis para ... more O presente artigo aborda uma nova aplicação do método observacional na engenharia de túneis para a adaptação em tempo real do método de escavação e suporte. O método observacional é utilizado há muitos anos, no entanto não existe uma metodologia consistente e estruturada para a incorporação dos dados da monitorização na adaptação do sistema de suporte em tempo real. A metodologia proposta possibilitará a otimização do sistema de suporte e do custo total da obra, tal como um aumento da segurança nos trabalhos de escavação. Primeiramente, são propostos critérios limite para os deslocamentos e tensões no maciço. Durante a fase de projecto são construídos gráficos de suporte de consulta rápida durante a fase de construção para a realização da adaptação referida. Caso não existam gráficos disponíveis para a situação específica em análise, é necessário o recurso a cálculos de retroanálise. A metodologia foi aplicada ao túnel de "Bois de Peu", composto por dois túneis paralelos com um comprimento superior a 500 m. Este caso de estudo apresentava um elevado nível de incerteza relativa à heterogenidade do solo e consequentemente à definição dos parâmetros geomecânicos. A metodologia foi aplicada em 4 secções embora se apresentem os resultados para apenas duas. Foi possível confirmar o potencial da aplicação da metodologia na adaptação em tempo real do sistema de suporte, assim como a importância de existir um plano de monitorização específico e de qualidade no aperfeiçoamento dos processos de retroanálise.

2 Terre Armee Internationale, 1 bis, rue du Petit-Clamart - 78140 Velizy-Villacoublay - France AB... more 2 Terre Armee Internationale, 1 bis, rue du Petit-Clamart - 78140 Velizy-Villacoublay - France ABSTRACT: The reinforcements used in Reinforced Earth structures are most commonly made of ribbed steel strips or of geosynthetic straps. The behaviour of the later is more complex, due to their extensibility. However, the design methods used for the geosynthetic straps are based on a classical friction model. This simple model considers the same design assumptions for the geosynthetic straps as for inextensible reinforcements and does not take into account the strap progressive mobilization. If this is justified for the justification of the structure stability, the detailed behaviour is supposed to be different. To highlight the influence of the synthetic reinforcement extensibility, several pull out tests were carried out on Geostraps developed by Terre Armee Internationale. These tests allow us to monitor the imposed tension as well as the displacements of several points along the strap. Then, back analyses of these results using an analytical model allowed to define the interaction parameters between the soil mass and the synthetic reinforcements. The design methods created for the structures reinforced by metallic reinforcements and thus inextensible were brought to be extrapolated to extensible materials. The difference in behaviour of these two types of reinforcement induces the definition of elongation limits beyond which the behaviour of the structure may be different. In order to adapt and to improve these methods, a better knowledge of the interaction between the soil mass and the reinforcement strips seems necessary. Most of the design methods used for the structures reinforced by geosynthetic straps are developed from the friction models based on the soil/geosynthetic interface friction model (Cambefort type, Fig. 2) and on the tensile-load linear elasticity of the inclusion (resulting from the Hooke's law, Fig. 1). This article presents an analytical method for analysing the pull-out tests on synthetic straps. This method is based on the classic friction laws (Schlosser & Guilloux 1981, Segrestin & Bastick 1996) and permits to reproduce the variation of tensile-load and displacements along the reinforcement strip. Back analysis of the analytical model on the experimental results allows us to validate this analytical development. 2 ANALYTICAL FRICTION MODELS DEVELOPMENT The friction model permits to determine the tensile-load/displacement relationship and the mobilized deformation along a pulled-out reinforcement. The determination

This paper presents a reliability-based approach for the threedimensional analysis of the face st... more This paper presents a reliability-based approach for the threedimensional analysis of the face stability of a shallow circular tunnel driven by a pressurized shield. Only the collapse failure mode of the ultimate limit state is studied. The deterministic model is based on the upper-bound method of the limit analysis theory. The random variables used are the soil shear strength parameters. The Hasofer-Lind reliability index and the failure probability were determined. A sensitivity analysis was also performed. It was shown that (i) the assumption of negative correlation between the soil shear strength parameters gives a greater reliability of the tunnel face against collapse, with respect to the hypothesis of uncorrelated variables, (ii) the failure probability is much more influenced by the coefficient of variation of the angle of internal friction than that of the cohesion and (iii) when no correlation between shear strength parameters is considered, a more spread out CDF of the tunnel pressure was obtained in comparison to the case of correlated shear strength parameters.

The present paper makes use of a 2D limit analysis mechanism developped in Mollon et al. 2011 to ... more The present paper makes use of a 2D limit analysis mechanism developped in Mollon et al. 2011 to study the influence of the scale of fluctuation of the friction angle in a soil mass on the critical collapse pressure of a pressurized tunnel face. The variability of the soil is simulated by random fields in the framework of the Karhunen-Loeve Expansion method, with various scales of fluctuation. A Monte-Carlo sampling scheme is used to examine the probabilistic impact of this variability as well as possible emergent behaviours that may be qualitatively different from well known behaviours associated with homogeneous sand. Probabilistic results show that L/D ratio (i.e. autocorrelation length of the friction angle random field, over tunnel diameter D) has an important influence on the dispersion of the critical collapse pressure. For a small to moderate value of this scale of fluctuation with respect to the tunnel diameter, it appears that there are several critical positions of the failure mechanism, whereas such phenomenon is unlikely for large values of L/D.

The Collocation-based Stochastic Response Surface Methodology (CSRSM) is a powerful probabilistic... more The Collocation-based Stochastic Response Surface Methodology (CSRSM) is a powerful probabilistic method. It aims at replacing a complex deterministic model by a simple analytical expression (called meta-model) to reduce the time cost of the classical probabilistic methods. The meta-model is based on a Polynomial Chaos Expansion (PCE). The coefficients of the PCE are computed in this paper by regression from the response of the deterministic model at a limited number of collocation points. The conventional formalism of CSRSM requires performing a new set of deterministic computations each time the probabilistic parameters of the input random variables are slightly modified. An extension of CSRSM is therefore proposed in this paper. It allows the realization of a parametric study at a limited time cost without loss of accuracy. This is demonstrated by comparing the results obtained from the original CSRSM and its extension when performing a parametric study concerning the stability analysis of a pressurized tunnel face.

Environmental Earth Sciences, 2014

During the construction of twin tunnels excavated in close proximity to each other, the predictio... more During the construction of twin tunnels excavated in close proximity to each other, the prediction of the influence of a new tunnel construction on an already existing one plays an important role in the design and construction of the tunnels. The researches in the literature indicate that this influence depends to a great extent on the distance between the tunnels. However, most of the reported cases in the literature on the mechanized excavation of twin tunnels have focused on the effects of the relative position between the two tunnels on surface settlements. Some of them have dealt with the behaviour of the tunnel structure through the use of simplified numerical models. The numerical investigation performed in this study, using the FLAC 3D finite difference code, has made it possible to predict the impact between tunnels using full three-dimensional simulations, in which most of the elements of a mechanized tunnel process have been modelled. The effects of tunnel distance on the structural forces induced in both tunnels, and the displacements in the surrounding ground have been highlighted. A modification has been made to the superposition method to predict the settlement surface trough over twin tunnels.

Journal of Geotechnical and Geoenvironmental Engineering, 2010

The aim of this paper is to determine the face collapse pressure of a circular tunnel driven by a... more The aim of this paper is to determine the face collapse pressure of a circular tunnel driven by a pressurized shield. The analysis is performed in the framework of the kinematical approach of limit analysis theory. It is based on a translational three-dimensional multiblock failure mechanism. The present failure mechanism has a significant advantage with respect to the existing limit analysis mechanisms developed in the case of a frictional soil: it takes into account the entire circular tunnel face and not only an inscribed ellipse to this circular area. This was made possible by the use of a spatial discretization technique. Hence, the three-dimensional failure surface was generated "point by point" instead of simple use of existing standard geometric shapes such as cones or cylinders. The numerical results have shown that a multiblock mechanism composed of three blocks is a good compromise between computation time and results accuracy. The present method significantly improves the best available solutions of the collapse pressure given by other kinematical approaches. Design charts are given in the case of a frictional and cohesive soil for practical use in geotechnical engineering.

Journal of Geotechnical and Geoenvironmental Engineering, 2009

A probabilistic analysis of a shallow circular tunnel driven by a pressurized shield in a frictio... more A probabilistic analysis of a shallow circular tunnel driven by a pressurized shield in a frictional and/or cohesive soil is presented. Both the ultimate limit state ͑ULS͒ and serviceability limit state ͑SLS͒ are considered in the analysis. Two deterministic models based on numerical simulations are used. The first one computes the tunnel collapse pressure and the second one calculates the maximal settlement due to the applied face pressure. The response surface methodology is utilized for the assessment of the Hasofer-Lind reliability index for both limit states. Only the soil shear strength parameters are considered as random variables while studying the ULS. However, for the SLS, both the shear strength parameters and Young's modulus of the soil are considered as random variables. For ULS, the assumption of uncorrelated variables was found conservative in comparison to the one of negatively correlated parameters. For both ULS and SLS, the assumption of nonnormal distribution for the random variables has almost no effect on the reliability index for the practical range of values of the applied pressure. Finally, it was found that the system reliability depends on both limit states. Notice however that the contribution of ULS to the system reliability was not significant. Thus, SLS can be used alone for the assessment of the tunnel reliability.

Journal of Geotechnical and Geoenvironmental Engineering, 2014

ABSTRACT Soil reinforcement by vertical rigid piles is a suitable technique to solve soft-soil fo... more ABSTRACT Soil reinforcement by vertical rigid piles is a suitable technique to solve soft-soil foundation problems. This technique consists of transferring the load of a pile-supported structure to a resistant, less compressible soil layer. The loads are transferred on pile heads by arching mechanisms in an earth-platform located between piles and structure. The role of the earth-platform is to distribute the loads among the piles and to minimize the fraction of the load applied on the soft compressible soil. Centrifuge tests are performed at 12and20xg levels of acceleration with a specific apparatus containing 63 rigid piles. The behavior of a granular earth-platform with rigid pile reinforcement is studied. The granular earth-platform is simulated with Hostun sand. The physical model is widely instrumented to compare the load-transfer efficiency and the surface settlements for several geometrical configurations. The influence of the height of the earth-platform and the spacing between the piles on load-transfer mechanisms are discussed as well as the effect of a cyclic loading. In this study, the low-height earth-platform is investigated to simulate extreme geometrical conditions. These low-height earth-platforms are suitable for low compressible soils, and in some cases a concrete slab is used above this platform.