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Tesi amb menció de Doctorat Internacional, Tesi en modalitat de cotutela: Universitat Politècnica de Catalunya i Université libre de Bruxelles, Tesi en modalitat de compendi de publicacions, (English) Interferometry with Synthetic Aperture Radar (InSAR) is a remote sensing technique to measure displacements of the observed surface, either the ground or any structure on it. Although the systematic acquisition of SAR data from satellites started in the 1990s, InSAR is a technique still in development. The continuous improvement of the successive SAR satellite constellations in terms of reliability, revisit time, spatial resolution and data accessibility, and the processing techniques of SAR data in the estimation of surface displacements is improving the performance of InSAR. Thus, this doctoral thesis aims to explore the new opportunities that InSAR offers today. In particular, the objectives are, first, to explore novel contributions of InSAR in geological engineering, more specifically, in land monitoring and the hydrogeological characterisation of the ground; and, second, to do so while covering both qualitative and quantitative applications at both regional and local scales. These goals are addressed through four questions. The first question aims to investigate whether InSAR’s spatial resolution and precision are high enough today to monitor ground deformation at such a local scale and in such a changing environment as a construction site. Applied to the ground deformation induced by the dewatering of civil engineering works, InSAR provides a much more complete view and understanding of the observed phenomena than more common alternative techniques such as levelling. However, levelling usually provides more precise measurements. Thus, a combination of both techniques will improve and make the monitoring of civil engineering works more reliable. The second question is whether, because of its spatial data density and its precision, InSAR is suitable for the numerical modelling of extensive ground deformation phenomena. The results achieved thanks to InSAR data in the hydromechanical numerical modelling of regional and long-term ground subsidence relat, (Català) La interferometria amb radar d'obertura sintètica (InSAR) és una tècnica de teledetecció que mesura desplaçaments de la superfície observada, sigui el terreny o qualsevol estructura situada a sobre. Tot i que l'adquisició sistemàtica de dades SAR des de satèl·lit va començar a la dècada del 1990, l’InSAR és una tècnica encara en desenvolupament. Les constel·lacions de satèl·lits SAR successives van millorant en termes de fiabilitat, temps de revisita, resolució espacial i accessibilitat de les dades, com també ho fan les tècniques de processament de les dades SAR en l'estimació del desplaçament de la superfície. Com a resultat, les prestacions de l'InSAR van millorant, de manera que l’objectiu d’aquesta tesi és explorar les noves oportunitats que l'InSAR ofereix avui en dia. Concretament, els objectius són (i) explorar noves aportacions de l'InSAR en l’enginyeria geològica, més específicament en el monitoratge i la caracterització hidrogeològica del terreny, i (ii) fer-ho tot cobrint aplicacions tant qualitatives com quantitatives a escales tant regionals com locals. Aquests objectius s'aborden a través de quatre preguntes. La primera investiga si la resolució espacial i la precisió de l'InSAR són suficients avui per a monitorar deformacions del terreny a una escala tan local i en entorns tan canviants com obres d’enginyeria civil. Aplicada a la deformació del terreny associada al drenatge d'unes obres, l’InSAR aporta una visió i una comprensió dels fenòmens observats molt més completes que les tècniques alternatives més habituals com l'anivellació topogràfica. Tanmateix, l’anivellació proporciona mesures generalment més precises. Així, la combinació d'ambdues tècniques pot millorar i augmentar la fiabilitat del monitoratge d’obres d'enginyeria civil. La segona pregunta explora si, per la seva densitat espacial de dades i la seva precisió, l’InSAR és apta per a la modelització numèrica de deformacions extensives del terreny. Els resultats obtinguts gràcies, (Español) La interferometria con radar de apertura sintética (InSAR) es una técnica de teledetección que mesura desplazamientos de la superficie observada, sea el terreno o cualquier estructura situada encima. A pesar de que la adquisición sistemática de datos SAR desde satélite empezó en la década del 1990, el InSAR es una técnica todavía en desarrollo. Las constelaciones de satélites SAR sucesivas van mejorando en términos de fiabilidad, tiempo de revisita, resolución espacial y accesibilidad de los datos, como también lo hacen las técnicas de procesamiento de los datos SAR en la estimación del desplazamiento de la superficie. Como resultado, las prestaciones de la InSAR van mejorando, de forma que el objetivo de esta tesis es explorar las nuevas oportunidades que la InSAR ofrece hoy en día. Concretamente, los objetivos son (y) explorar nuevas aportaciones de la InSAR en la ingeniería geológica, más específicamente en la monitorización y la caracterización hidrogeológica del terreno, y (ii) hacerlo cubriendo aplicaciones tanto cualitativas como cuantitativas a escalas tanto regionales como locales. Estos objetivos se abordan a través de cuatro preguntas. La primera investiga si la resolución espacial y la precisión de la InSAR son suficientes hoy para monitorizar deformaciones del terreno en una escala tan local y en entornos tan cambiantes como obras de ingeniería civil. Aplicada a la deformación del terreno asociada al drenaje de unas obras, la InSAR aporta una visión y una comprensión de los fenómenos observados mucho más completas que las técnicas alternativas más habituales como la nivelación topográfica. Aun así, la nivelación proporciona medidas generalmente más precisas. Así, la combinación de ambas técnicas puede mejorar y aumentar la fiabilidad de la monitorización de obras de ingeniería civil. La segunda pregunta explora si, por su densidad espacial de datos y su precisión, la InSAR es apta para la modelización numérica de deformaciones extensivas del t, Postprint (published version)

L'interférométrie avec radar à synthèse d'ouverture (InSAR) est une technique de télédétection permettant de mesurer les déplacements à la surface, que ce soit du sol ou de toute structure située dessus. Bien que l'acquisition systématique des données SAR à partir de satellites ait commencé dans les années 1990, InSAR est une technique encore en développement. L'amélioration continue en termes de fiabilité, temps de revisite, résolution spatiale et accessibilité des données des différentes constellations de satellites SAR, ainsi que du traitement des données SAR, améliorent la performance de l'InSAR dans l’estimation des déplacements de la surface. Ainsi, cette thèse de doctorat vise à explorer les nouvelles opportunités que l’InSAR offre aujourd'hui. En particulier, l’objectif est d’explorer les nouvelles contributions de l’InSAR en géologie de l’ingénieur pour le suivi du terrain et la caractérisation hydrogéologique. Ce travail de recherche veille à explorer les opportunités de l’InSAR tant pour des études qualitatives que quantitatives, avec des échelles de zone d’étude tant régionales que locales. Ces objectifs sont abordés à travers quatre questions. La première vise à déterminer si la résolution spatiale et la précision de l’InSAR sont aujourd’hui suffisantes pour monitorer la déformation du sol à une échelle aussi locale et dans des environnements aussi changeants qu’un chantier de génie civil. L’étude montre que pour des déplacements de la surface du sol induits par des opérations de rabattement de la nappe aquifère, l’InSAR apporte une caractérisation plus large et une compréhension beaucoup plus fine des phénomènes observés que des techniques alternatives plus standards telles que le nivellement. Cependant, le nivellement fournit généralement des mesures plus précises. Ainsi, une combinaison des deux techniques permettra d’améliorer et de rendre plus fiable le suivi des travaux de génie civil. La deuxième question est de vérifier si, en raison de sa densi, Interferometry with Synthetic Aperture Radar (InSAR) is a remote sensing technique to measure displacements of the observed surface, either the ground or any structure on it. Although the systematic acquisition of SAR data from satellites started in the 1990s, InSAR is a technique still in development. The continuous improvement of the successive SAR satellite constellations in terms of reliability, revisit time, spatial resolution and data accessibility, and the processing techniques of SAR data in the estimation of the surface displacement are improving the performance of InSAR. Thus, this doctoral thesis aims to explore the new opportunities that InSAR offers today. In particular, the objectives are, first, to explore novel contributions of InSAR in geological engineering, more specifically, in land monitoring and the hydrogeological characterisation of the ground; and, second, to do so while covering both qualitative and quantitative approaches at both regional and local scales. These goals are addressed through four questions. The first question aims to investigate whether InSAR’s spatial resolution and precision are high enough today to monitor ground deformation at such a local scale and in such a changing environment as a construction site. Applied to the ground deformation induced by the dewatering of civil engineering works, InSAR provides a much more complete view and understanding of the observed phenomena than more common alternative techniques such as levelling. However, levelling usually provides more precise measurements. Thus, a combination of both techniques will improve and make the monitoring of civil engineering works more reliable. The second question is whether, because of its spatial data density and its precision, InSAR is suitable for the numerical modelling of extensive ground deformation phenomena. The results achieved thanks to InSAR data in the hydromechanical numerical modelling of regional and long-term ground subsidence related to th, La interferometria amb radar d'obertura sintètica (InSAR) és una tècnica de teledetecció que mesura desplaçaments de la superfície observada, sigui el terreny o qualsevol estructura situada a sobre. Tot i que l'adquisició sistemàtica de dades SAR des de satèl·lit va començar a la dècada del 1990, l’InSAR és una tècnica encara en desenvolupament. Les constel·lacions de satèl·lits SAR successives van millorant en termes de fiabilitat, temps de revisita, resolució espacial i accessibilitat de les dades, com també ho fan les tècniques de processament de les dades SAR en l'estimació del desplaçament de la superfície. Com a resultat, les prestacions de l'InSAR van millorant, de manera que l’objectiu d’aquesta tesi és explorar les noves oportunitats que l'InSAR ofereix avui en dia. Concretament, els objectius són (i) explorar noves aportacions de l'InSAR en l’enginyeria geològica, més específicament en el monitoratge i la caracterització hidrogeològica del terreny, i (ii) fer-ho tot cobrint aplicacions tant qualitatives com quantitatives a escales tant regionals com locals. Aquests objectius s'aborden a través de quatre preguntes. La primera investiga si la resolució espacial i la precisió de l'InSAR són suficients avui per a monitorar deformacions del terreny a una escala tan local i en entorns tan canviants com obres d’enginyeria civil. Aplicada a la deformació del terreny associada al drenatge d'unes obres, l’InSAR aporta una visió i una comprensió dels fenòmens observats molt més completes que les tècniques alternatives més habituals com l'anivellació topogràfica. Tanmateix, l’anivellació proporciona mesures generalment més precises. Així, la combinació d'ambdues tècniques pot millorar i augmentar la fiabilitat del monitoratge d’obres d'enginyeria civil. La segona pregunta explora si, per la seva densitat espacial de dades i la seva precisió, l’InSAR és apta per a la modelització numèrica de deformacions extensives del terreny. Els resultats obtinguts gràcies a les dad, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/published

The necessity to house the worldwide growing population is making the production of Portland cement (PC) grow alongside with its CO2 emissions in the atmosphere. In order to reduce said emissions, the scientific community is looking for viable and greener alternatives with comparable mechanical properties and good durability. Alkali-activated materials seem to represent a possible replacement to PC, even though their long-term durability is still not fully understood.One of the main issues for the durability of construction materials is the volume stability in drying conditions, that is how the volume of the material decreases when exposed to environmental conditions. The main consequence of the volume contraction is the development of microcracks which reduce the mechanical strength, allow for water vapour and CO2 to penetrate further inside the material, and may also lead to failure of the structure. In order to assess the long-term durability of a material is therefore crucial to understand how it shrinks according to the different external conditions.The present study focuses on the activation of Blast Furnace Slag (BFS) using different sodium hydroxide solutions and takes into account three main aspects of durability: the tendency to cracking in restrained conditions, the pore structure and hydraulic conductivity of the material, and the drying shrinkage in free conditions. The first experimental campaign on restrained shrinkage has been conducted using the ring test coupled with the assessment of the mechanical properties both in sealed and drying conditions; the goal is to understand when the formation of microcracks takes place and what is the maximum deformation the material can endure before failure. The second experimental campaign modelled the total porosity, the pore size distribution, and the hydraulic conductivity of the material based on the mass variation of the material exposed to different relative humidity levels. Finally, the third experimental, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

A methodology to characterize the main hydro-geothermal parameters of saturated and unsaturated ground layers, such as intrinsic thermal conductivity, volumetric heat capacity and groundwater velocity is proposed, based on the monitoring of the temperature plume around an activated borehole heat exchanger (BHE). The methodology is applied on an experimental platform composed of four BHEs. Based on the expected lithology and approximative groundwater fluxes direction, one BHE is thermally activated with a pre-determined heat injection and duration. The temperature evolution is recorded by means of PT100 sensors in the activated BHE and in the three non-activated BHEs, at three different depths in the saturated and unsaturated domain of an unconfined aquifer crossed by the BHEs. From an analytical solution considering conductive, advective and dispersive heat transfers, the hydro-geothermal parameters of the ground are obtained by fitting the measured to the predicted temperatures evolution. The effect of the possible inclination of the measuring boreholes is evaluated with the analytical solution. The obtained hydro-geothermal parameters demonstrate the important role of the saturated aquifer that significantly enhances the apparent thermal conductivity of the ground and, in case of groundwater flows, induces an anisotropic propagation of the temperature plume., SCOPUS: ar.j, info:eu-repo/semantics/published

Until the advent of remote sensing techniques, the study of regional subsidence was hampered by the rarity and sparsity of field measurements of ground displacement, which led to a significant uncertainty regarding the representativeness of the calibration data used in the modelling of these phenomena and the reliability of derived predictions. This paper explores the unique potential of Persistent Scatterer Interferometry with Synthetic Aperture Radar (PS-InSAR) in the hydromechanical modelling of a large-scale, long-term subsidence occurring in the provinces of West- and East-Flanders, Belgium, related to the overexploitation of the deep aquifer system in the region. PS-InSAR has been used, not only to describe and characterise the ground subsidence and identify representative locations, but also to calibrate the hydromechanical parameters of the ground and validate the results of a numerical model. PS-InSAR has proven to be essential to improve the calibration and reach a set of parameters (i) coherent with the hydrogeology of the study area, (ii) coherent between different deforming zones and (iii) able to reproduce the dynamics of the observed ground subsidence. Thus, PS-InSAR enables to accurately reproduce, understand and simulate the compaction of an aquifer system and, ultimately, design adequate and optimised management policies., SCOPUS: ar.j, info:eu-repo/semantics/published

Predictions of the unsaturated shear strength with generalized effective stress-based approaches disregard the non-uniform microstructure of remolded fine-grained soils. The study aims at investigating the adequacy of microstructurally-based effective stress to predict the unsaturated shear strength of remolded fine-grained soils over a wide range of suctions. For that purpose, shear strength data are acquired on a silty clay soil compacted at two different dry densities through suction-controlled triaxial tests and unconsolidated triaxial tests at constant water content. The microstructure of the soil at the as-compacted state is determined with Mercury Intrusion Porosimetry and is directly incorporated in different expressions of microstructurally-based effective stress available in the literature. The experimental data suggest that compared to the generalized effective stress, microstructurally-based effective stress expressions provide better predictions of the unsaturated shear strength, especially at high suctions. Also, the use of microstructurally-based effective stress is particularly relevant for remolded fine-grained soils compacted at high dry densities, i.e. with a low proportion of macropores., SCOPUS: ar.j, info:eu-repo/semantics/published

Until the advent of remote sensing techniques, the study of regional subsidence was hampered by the rarity and sparsity of field measurements of ground displacement, which led to a significant uncertainty regarding the representativeness of the calibration data used in the modelling of these phenomena and the reliability of derived predictions. This paper explores the unique potential of Persistent Scatterer Interferometry with Synthetic Aperture Radar (PS-InSAR) in the hydromechanical modelling of a large-scale, long-term subsidence occurring in the provinces of West- and East-Flanders, Belgium, related to the overexploitation of the deep aquifer system in the region. PS-InSAR has been used, not only to describe and characterise the ground subsidence and identify representative locations, but also to calibrate the hydromechanical parameters of the ground and validate the results of a numerical model. PS-InSAR has proven to be essential to improve the calibration and reach a set of parameters (i) coherent with the hydrogeology of the study area, (ii) coherent between different deforming zones and (iii) able to reproduce the dynamics of the observed ground subsidence. Thus, PS-InSAR enables to accurately reproduce, understand and simulate the compaction of an aquifer system and, ultimately, design adequate and optimised management policies.

info:eu-repo/semantics/inPress

This is the peer reviewed version of the following article: Nasika, C. [et al.]. Discrete empirical interpolation for hyper-reduction of hydro-mechanical problems in groundwater flow through soil. "International journal for numerical and analytical methods in geomechanics", 10 Abril 2023, vol. 47, núm. 5, p. 667-693, which has been published in final form at https://onlinelibrary.wiley.com/doi/10.1002/nag.3487. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited., The recent surge in the availability of sensor data and computational resources has fostered the development of technologies for optimization, control, and monitoring of large infrastructures, integrating data and numerical modeling. The major bottleneck in this type of technologies is the model response time, since repetitive solutions are typically required. To reduce the computational time, reduced order models (ROMs) are used as surrogates for expensive finite element (FE) simulations enabling the use of complex models in this type of applications. In this work, ROMs are explored for the solution of the fully coupled hydro-mechanical system of equations that governs the water flow through partially saturated soil. The POD-based Reduced Basis Method and the Discrete Empirical Interpolation Method (DEIM), as well as its localized version (LDEIM), are examined in solving a parametrized problem simulating the mechanical loading of an embankment dam. Hydraulic and mechanical soil properties are considered as parameters. It is shown that the combination of these methods results in simulations that require 1/10 to 1/100 of the FE response time. Moreover, the method is shown to yield scaling efficiency gains with increasing problem size., Peer Reviewed, Postprint (published version)

The recent surge in the availability of sensor data and computational resources has fostered the development of technologies for optimization, control and monitoring of large infrastructures, integrating data and numerical modeling. The major bottleneck in this type of technologies is the model response time, since repetitive solutions are typically required. To reduce the computational time, Reduced Order Models (ROMs) are used as surrogates for expensive Finite Element (FE) simulations enabling the use of complex models in this type of applications. In this work, ROMs are explored for the solution of the fully coupled hydro-mechanical system of equations that governs the water flow through partially saturated soil. The POD-based Reduced Basis method and the Discrete Empirical Interpolation Method (DEIM), as well as its localized version (LDEIM), are examined in solving a parametrized problem simulating the mechanical loading of an embankment dam. Hydraulic and mechanical soil properties are considered as parameters. It is shown that the combination of these methods results in simulations that require 1/10 to 1/100 of the FE response time. Moreover, the method is shown to yield scaling efficiency gains with increasing problem size., SCOPUS: ar.j, info:eu-repo/semantics/published

Ground source heat pump (GSHP) system combined with boreholes heat exchangers (BHEs) is increasing worldwide. This technology consists in circulating a fluid within a U-shaped pipe to generate heat exchanges between a BHE and the ground surrounding it, thanks to the temperature difference between the fluid and the ground. BHE can be used for extracting heat (for heating purpose) or injecting heat (for cooling purpose) from/into the ground. In this framework, the presence of groundwater enhances the heat exchanges, as the intrinsic thermal conductivity increases when the pore space is filled by water. Additionally, groundwater fluxes induce advective and dispersive heat exchanges. However, the huge majority of existing norms to dimension multi-BHEs fields only consider conductive heat exchanges, using an apparent ground thermal conductivity inferred from a thermal response test and that generally includes the combined effect of conductive, advective and dispersive heat transfers. The real heat transfers are thus not properly considered in most of the design approaches. Besides, the determination of both the intrinsic ground thermal conductivity and groundwater fluxes (magnitude and direction) requires the characterization of the temperature evolution, not only along an activated BHE, but also around it. However, there is nowadays a lack of experimental studies measuring the heat plume propagation around an activated BHE. Therefore, the first contribution of this thesis is to develop an experimental set-up able to monitor the temperature field around an activated BHE. The set-up is implemented on a previously-developed experimental platform made up of four BHEs, that cross an unconfined aquifer. The thermal activation of one BHE and the monitoring of the temperature through PT100 sensors installed at different depths in the activated and non-activated BHEs provide an appropriate characterization of the heat plume propagation in both saturated and unsaturated domains o, info:eu-repo/semantics/nonPublished

Ground source heat pump (GSHP) system combined with boreholes heat exchangers (BHEs) is increasing worldwide. This technology consists in circulating a fluid within a U-shaped pipe to generate heat exchanges between a BHE and the ground surrounding it, thanks to the temperature difference between the fluid and the ground. BHE can be used for extracting heat (for heating purpose) or injecting heat (for cooling purpose) from/into the ground. In this framework, the presence of groundwater enhances the heat exchanges, as the intrinsic thermal conductivity increases when the pore space is filled by water. Additionally, groundwater fluxes induce advective and dispersive heat exchanges. However, the huge majority of existing norms to dimension multi-BHEs fields only consider conductive heat exchanges, using an apparent ground thermal conductivity inferred from a thermal response test and that generally includes the combined effect of conductive, advective and dispersive heat transfers. The real heat transfers are thus not properly considered in most of the design approaches. Besides, the determination of both the intrinsic ground thermal conductivity and groundwater fluxes (magnitude and direction) requires the characterization of the temperature evolution, not only along an activated BHE, but also around it. However, there is nowadays a lack of experimental studies measuring the heat plume propagation around an activated BHE. Therefore, the first contribution of this thesis is to develop an experimental set-up able to monitor the temperature field around an activated BHE. The set-up is implemented on a previously-developed experimental platform made up of four BHEs, that cross an unconfined aquifer. The thermal activation of one BHE and the monitoring of the temperature through PT100 sensors installed at different depths in the activated and non-activated BHEs provide an appropriate characterization of the heat plume propagation in both saturated and unsaturated domains o, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

The latest monitoring and asset management technologies for large infrastruc- tures involve digital representations that integrate information and physical models, exist in parallel to the real-life structures, and are continuously up- dated based on assimilated sensor data, in order to accurately represent the actual conditions in the structures. This type of technology is often referred to as Digital Twin. The implementation of such cutting-edge technology in monitoring assets like tailings dams, or embankment dams in general, and other large structures, implies the development of highly efficient numerical tools that, combined with sensor data, may support rapid, informed decision making.For the particular case of embankment dams, enabling this type of tech- nology requires an efficient numerical model that describes the coupled hydro-mechanical phenomena, pertinent to a dam functioning and safety. This may for instance be a Finite Elements (FE) model, describing the groundwater flow through unsaturated porous geomaterials.The process of updating and calibrating a model, such as the above mentioned FE model, based on sensor data is typically referred to as data assimilation. Often, this is achieved via an optimization approach, where a specific problem is solved multiple times for various parametric values, in search for the values that best describe the sensor data. The bottleneck in this type of application is typically the cost of multiple evaluations of the model, that may become prohibitive when the underlying FE model is large. In order to enable such applications, the present work proposes Model Order Reduction (MOR) methods tailored to the hydro-mechanical nonlinear problem at hand.MOR aims at the creation of a surrogate model that seeks an approximation of the FE solution in a reduced-order space. This is achieved by applying an offline-online strategy. In the offline stage, the solution manifold of thefull-order problem is sampled, in order to identify, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

The present work investigates the desiccation effects on a lime-treated silty clay and compare it with the non-treated equivalent material. Original experimental techniques have been developed to control suction conditions, to track volume variations and cracks occurrence upon drying. Free and constrained desiccations are performed to evaluate the shrinkage potential (for free drying) and the conditions of desiccation crack triggering (upon constrained drying). Also, indirect tensile tests and uniaxial compression tests are carried out to evaluate the strength and stiffness at various suctions. In addition, the effects of the compaction mode, dry density and suction on the tensile strength have been investigated in a systematic way. Those investigations have been performed on natural and lime-treated compacted silty clay in order to emphasize the benefits of the lime treatment in the triggering and/or mitigation of the cracking process. To simulate the field conditions of compaction and obtain specimens having geomechanical properties as close as possible to the real material on site, the particular kneading compaction process in a CBR mould was largely used, and the final specimens were cut at required sizes with a milling machine numerically controlled by computer (CNC). At the end, generalized effective stress framework with an effective stress parameter calibrated according to a power law is used to provide a constitutive interpretation of the occurrence of desiccation cracks in relation with the water retention properties, the soil stiffness, the tensile strength and the geometrical constraints of the soil specimens. For the used compacted materials, it is demonstrated that the lime treatment postpones the occurrence of desiccation cracks that are triggered at higher suctions. So, lime treatment plays a favourable role in the reduction of shrinkage and crack occurrence of soft soils subject to drying., Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

Fused Filament Fabrication (FFF) is an extrusion-based Additive Manufacturing method widely used in various industries for prototyping applications. Since FFF's invention in the 1980s, this technology has undergone numerous advancements in terms of available material, software and equipment. Nevertheless, FFF parts are often limited to non-critical, non-load-bearing applications, partly because the existing design and manufacturing tools do not capitalize on FFF's high design freedom. In particular, the slicing software that generates printing instructions prints filaments in predefined patterns and cannot realize filament paths that are locally optimized to enhance the structural performance, thus, hindering the best utilization of FFF parts for load-bearing purposes. The current thesis aims to develop dedicated tools for designing and printing optimized filament paths for improved structural performance from FFF parts. First, an algorithmic framework that optimizes the in-plane filament paths for minimum compliance of FFF structures is presented, particularly focusing on obtaining production-ready design solutions by including the manufacturing constraints in the optimization process. Then, a new filament deposition algorithm is proposed to address the manufacturability issues observed in existing optimization strategies. The proposed algorithm accepts the point-wise orientation fields resulting from the optimization procedures and deploy filaments along the orientation fields to realize optimized designs. Both the contributions facilitate the seamless production of structural FFF parts, which we prove by applying them to design structurally-informed filament trajectories and printing the parts., Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

This work focuses on the development and employment of advanced numerical finite element modelling in reinforced concrete (RC) structures subjected to two accidental loads: sudden column loss and fire. A corotational 2D multilayered Bernoulli beam approach is employed in a correlated reduced Latin Hypercube sampling-based framework where uncertain model parameters are incorporated for the material behavior and cross sectional geometry. These uncertainties are investigated and shown to influence significantly the structural response, being the main focus of this contribution. The structural response of a realistic RC structure subjected to column loss when incorporating material properties variability is investigated in a dynamic approach (geometrical non-linearities coupled to layer plasticity and fracture) where the influence of each random variable (RV) is quantified in a Latin Hypercube Sampling (LHS) approach spanning over 12.000 simulations and leading to recommendations to mitigate progressive collapse: correct design of stirrups and good choice of steel reinforcement quality. The set of uncertain model parameters is extended by geometrical parameters of the cross section of the beam/frame structural elements when a stochastic analysis of the structural response and fire resistance is targeted. The corotational layered beam is adapted for simulations at elevated temperature by the implementation of a closed from thermal model coupled to the calculation of thermally induced strains from different sources and ensuring that all of the material parameters and their temperature evolution are adjusted to experimental data. The resulting efficient computational model compares favourably to experimental data from the literature, validating the proposed model. Its application in an LHS framework (+20.000 simulations) is shown to allow identifying a reduced set of dominant uncertain material and geometrical parameters for the simulation of RC members subjected to fire, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

In a large number of geo-environmental applications, it is essential to model coupled processes that depend on several design parameters such as material properties and geometrical features. Thermo-hydro-mechanical (THM) processes are, among others, key effects to consider in critical applications such as deep geological repository of hazardous nuclear waste. This thesis proposes novel model order reduction strategies to evaluate the thermo-hydro-mechanical response of porous media, taking into account the complexities involved in coupled processes for such applications. An a-posteriori model order reduction approach using reduced basis methods is applied to tackle the high-dimensional parametric THM system. The reduction is based on an offline-online stage strategy. In the offline stage, reduced subspaces are constructed by a greedy adaptive procedure and in the online stage, multi-subspace projection is performed to quickly obtain the coupled THM response at any value of the design parameter. The effectiveness of the model reduction strategies is demonstrated through realistic parametrized problems in large-scale geomodels depicting the coupled processes in potential deep geological repository sites., Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

© 2022 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0, The use of Internet of Things (IoT) technologies is becoming a preferred solution for the assessment of tailings dams’ safety. Real-time sensor monitoring proves to be a key tool for reducing the risk related to these ever-evolving earth-fill structures, that exhibit a high rate of sudden and extremely hazardous failures. In order to optimally exploit real-time embankment monitoring, one major hindrance has to be overcome: the creation of a supporting numerical model for stability analysis, with rapid-enough response to perform data assimilation in real time. A model should therefore be built, such that its response can be obtained faster than the physical evolution of the phenomenon to be analyzed. In this work, Reduced Order Modeling (ROM) is used to boost computational efficiency in solving the coupled hydromechanical system of equations governing the problem. POD-based reduction has been studied in order to treat the problem of groundwater flow, coupled to the geomechanical problem. The Reduced Basis method is applied to the coupled hydro-mechanical equations that govern the flow of groundwater, that are made non-linear as a result of considering an unsaturated soil. The resulting model’s performance is assessed by solving a 2D and a 3D problem relevant to tailings dams’ safety. The ROM technique achieves a speedup of 3 to 15 times with respect to the full-order model (FOM) while maintaining high levels of accuracy., This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie SklodowskaCurie grant agreement No 764636, for the research project ProTechTion. We thank Professor Sebatian Olivella (Escola de Camins, Universitat Politècnica de Catalunya) for his much appreciated assistance. Pedro Díez and Sergio Zlotink are grateful for the financial support provided by the Spanish Ministry of Economy and Competitiveness (Grant agreement No. DPI2017-85139-C2-2-R), by the Generalitat de Catalunya (Grant agreement No. 2017-SGR-1278), and by project H2020-RISE MATH-ROCKS GA no 777778., Peer Reviewed, Postprint (author's final draft)

Nasopharyngeal swabs are considered the preferential collection method for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) diagnostics. Less invasive and simpler alternative sampling procedures, such as saliva collection, are desirable. We compared saliva specimens and nasopharyngeal (NP) swabs with respect to sensitivity in detecting SARS-CoV-2. A nasopharyngeal and two saliva specimens (collected by spitting or oral swabbing) were obtained from >2500 individuals. All samples were tested by RT-qPCR, detecting RNA of SARS-CoV-2. The test sensitivity was compared on the two saliva collections with the nasopharyngeal specimen for all subjects and stratified by symptom status and viral load. Of the 2850 patients for whom all three samples were available, 105 were positive on NP swab, whereas 32 and 23 were also positive on saliva spitting and saliva swabbing samples, respectively. The sensitivity of the RT-qPCR to detect SARS-CoV-2 among NP-positive patients was 30.5% (95% CI, 1.9%–40.2%) for saliva spitting and 21.9% (95% CI, 14.4%–31.0%) for saliva swabbing. However, when focusing on subjects with medium to high viral load, sensitivity on saliva increased substantially: 93.9% (95% CI, 79.8%–99.3%) and 76.9% (95% CI, 56.4%–91.0%) for spitting and swabbing, respectively, regardless of symptomatic status. Our results suggest that saliva cannot readily replace nasopharyngeal sampling for SARS-CoV-2 diagnostics but may enable identification of the most contagious cases with medium to high viral loads., SCOPUS: ar.j, info:eu-repo/semantics/published

The aim of this paper is to demonstrate how the integration of differential interferometric synthetic aperture radar (D-InSAR) and levelling improves the monitoring of ground deformation phenomena, thereby enabling their complete understanding. The complementarity between D-InSAR and levelling is illustrated through a case study of the construction of a road tunnel beneath Glòries Square, Barcelona; D-InSAR is employed to continuously monitor the works, notably the dewatering of the site. This study focuses primarily on D-InSAR data obtained from the processing of Sentinel-1A data following a persistent scatterer interferometry procedure. The spatial distribution of the deformation and its temporal evolution are analysed with detailed hydrogeological and piezometric data. The magnitude of deformation is discussed using levelling data and an analytical estimation based on the hydromechanical parameters of the ground obtained from a pre-existing hydrogeological numerical model and pumping tests. The D-InSAR results are shown to be essential for identifying the origin of ground deformation and the constraints on its spread. Such observations at the construction site and district (~2 km radius) scales with sub-centimetric deformation are precious contributions of D-InSAR data, whereas levelling offers a more accurate quantification of the deformation, although this remains an open issue to be further investigated., SCOPUS: ar.j, info:eu-repo/semantics/published

Closed-loop borehole heat exchangers (BHEs) are used for heating/cooling buildings. For the sustainable design of these systems, analytical solutions provide fast and flexible tools to investigate the subsurface thermal response. In this study, from an existing analytical solution which predicts temperature field for discontinuous heat extraction/injection of multi-BHEs field, is improved to consider the case of heterogeneous heat loads (HHLs), i.e. heat loads tuned independently for each BHE to improve the long-term heat refurbishment in the subsurface. Also, we implemented the concept of BHE thermal resistance in order to determine the heat carrier fluid temperature. To provide accurate extreme temperatures, two aspects were analysed: the time step discretization; and the temporal resolution of thermal loads. The requirement for defining hourly thermal loads was demonstrated in order to properly predict extreme temperatures in the subsurface, as would be the case in an optimization problem of multi-BHEs with HHLs. As a study case, we showed the interest of HHLs to reduce localized thermal exhaustion of the geothermal system and to reduce extreme temperature variations and thermal drift in the most critical BHEs., SCOPUS: ar.j, info:eu-repo/semantics/published

A methodology for the determination of lithology-based thermal conductivities at a regional scale is proposed, assigning a saturated and unsaturated thermal conductivity to each stratigraphic unit encountered in the region. Such a methodology is paramount for GIS-supported mapping of shallow geothermal energy at a regional scale. The analysis is primarily based on the interpretation of thermal response tests (TRT), assuming that the thermal conductivity determined during TRT is a thickness-weighted average of the individual thermal conductivity of each stratigraphic unit constituting the ground along a ground heat exchanger (GHE). Enhanced thermal response tests, reference geological material-based thermal conductivities and laboratory optical scanning tests achieved on remolded specimen from drilling cuttings are used to validate the results. The relevance of the methodology is illustrated through its application to the Brussels-Capital Region (Belgium), and consistent saturated and unsaturated thermal conductivities are obtained for each stratigraphic unit. An uncertainty analysis on the thermal conductivity is proposed, and its impact on the design of GHE is discussed. In most cases, the relative error on the ground thermal conductivity is lower than 10 %, and its impact on GHE length remains limited., SCOPUS: ar.j, info:eu-repo/semantics/published

This contribution presents an integrated and automated methodology for the computational analysis of permeability alterations in natural rocks under varying stress states, taking explicitly into account the complexity of the rock microstructure. The capacity of the methodology is highlighted on a subset of the microCT scans of a Vosges sandstone. After the generation of a high quality conformal mesh of the subset, isotropic compression at the scale of the microstructure is applied through FEM simulations. The adoption of non linear elastoplastic constitutive laws allows considering the local stress redistributions within the specimen. The mechanical loading of the subset highlights pore closures by local plastification. Permeability is evaluated at different confining pressures using the Lattice-Bolzmann method. Such a procedure allows analysing the impact of the pore space morphology (i.e. total porosity, pore size distribution, connectivity of the pore space, etc.) as well as the mechanical properties (i.e. stiffness and shear strength) on the evolution of the permeability under loading., info:eu-repo/semantics/published

The use of Internet of Things (IoT) technologies is becoming a preferred solution for the assessment of tailings dams safety. Real-time sensor monitoring proves to be a key tool for reducing the risk related to these ever-evolving earth-fill structures, that exhibit a high rate of sudden and hazardous failures. In order to optimally exploit real-time embankment monitoring, one major hindrance has to be overcome: the creation of a supporting numerical model for stability analysis, with rapid-enough response to perform data assimilation in real time. A model should be built, such that its response can be obtained faster than the physical evolution of the analyzed phenomenon. In this work, Reduced Order Modelling (ROM) is used to boost computational efficiency in solving the coupled hydro-mechanical system of equations governing the problem. The Reduced Basis method is applied to the coupled hydro-mechanical equations that govern the groundwater flow, that are made non-linear as a result of considering an unsaturated soil. The resulting model's performance is assessed by solving a 2D and a 3D problem relevant to tailings dams safety. The ROM technique achieves a speedup of 3 to 15 times with respect to the full-order model (FOM) while maintaining high levels of accuracy, info:eu-repo/semantics/published

The aim of this paper is to demonstrate how the integration of differential interferometric synthetic aperture radar (D-InSAR) and levelling improves the monitoring of ground deformation phenomena, thereby enabling their complete understanding. The complementarity between D-InSAR and levelling is illustrated through a case study of the construction of a road tunnel beneath Glòries Square, Barcelona; D-InSAR is employed to continuously monitor the works, notably the dewatering of the site. This study focuses primarily on D-InSAR data obtained from the processing of Sentinel-1A data following a persistent scatterer interferometry procedure. The spatial distribution of the deformation and its temporal evolution are analysed with detailed hydrogeological and piezometric data. The magnitude of deformation is discussed using levelling data and an analytical estimation based on the hydromechanical parameters of the ground obtained from a pre-existing hydrogeological numerical model and pumping tests. The D-InSAR results are shown to be essential for identifying the origin of ground deformation and the constraints on its spread. Such observations at the construction site and district (~2 km radius) scales with sub-centimetric deformation are precious contributions of D-InSAR data, whereas levelling offers a more accurate quantification of the deformation, although this remains an open issue to be further investigated.

The use of Internet of Things (IoT) technologies is becoming a preferred solution for the assessment of tailings dams' safety. Real-time sensor monitoring proves to be a key tool for reducing the risk related to these ever-evolving earth-fill structures, that exhibit a high rate of sudden and hazardous failures. In order to optimally exploit real-time embankment monitoring, one major hindrance has to be overcome: the creation of a supporting numerical model for stability analysis, with rapid-enough response to perform data assimilation in real time. A model should be built, such that its response can be obtained faster than the physical evolution of the analyzed phenomenon. In this work, Reduced Order Modelling (ROM) is used to boost computational efficiency in solving the coupled hydro-mechanical system of equations governing the problem. The Reduced Basis method is applied to the coupled hydro-mechanical equations that govern the groundwater flow, that are made non-linear as a result of considering an unsaturated soil. The resulting model's performance is assessed by solving a 2D and a 3D problem relevant to tailings dams' safety. The ROM technique achieves a speedup of 3 to 15 times with respect to the full-order model (FOM) while maintaining high levels of accuracy.

The coupled effects of climate change, sea-level rise, and land sinking in estuaries/alluvial plains prone to inundation and flooding mean that reliable estimation of land movements/subsidence is becoming more crucial. During the last few decades, land subsidence has been monitored by precise and continuous geodetic measurements either from space or using terrestrial techniques. Among them, the Persistent Scaterrer Interferometry (PSInSAR) technique is used on the entire Belgian territory to detect, map and interpret the identified ground movements observed since 1992. Here the research focuses on one of the biggest cities in Belgium that became the second European harbour with giant docks and the deepening of the Scheldt river allowing the navigation of the largest container vessels. The areas along the embankments of the Scheldt river and the harbour facilities are associated to Holocene fluviatile deposits overlain by recent landfills. These sedimentary deposits and human-made landfills are affected by important and ongoing land subsidence phenomena. The land subsidence process is highlighted by an annual average Line of Sight (LOS) velocity of about −3.4 mm/year during the years 1992–2001 (ERS1/2 datasets), followed by an annual average LOS velocity of about −2.71 mm/year and −2.11 mm/year, respectively, during the years 2003–2010 (ENVISAT) and 2016–2019 (Sentinel 1A). The Synthetic Aperture Radar (SAR) imagery data indicate a progressive decrease in the average annual velocities on a global scale independently of important local variations in different districts along the Scheldt river. On the contrary, the city centre and the old historic centre of Antwerp are not affected by negative LOS velocities, indicating stable ground conditions. A geological interpretation of this difference in settlement behaviour between the different areas is provided., SCOPUS: ar.j, info:eu-repo/semantics/published

Modern infrastructure monitoring technologies are often based on the fast response of a digital model of the asset for real-time predictions and/or control. In the case of earthfill dams, particularly tailings dams, the dynamic design and functioning of the structure can give rise to a need for realtime model calibration and data assimilation for accurate monitoring. However, these techniques suppose many queries on large models and are often too costly to be performed in real-time. To accelerate the model response and make feasible the incorporation of numerical modeling within the monitoring system, we propose using Model Order Reduction techniques in the transient thermohydro-mechanical system.The scope of this work is to create a model to support a sensor monitoring system of a tailings dam, by receiving sensor data of local pressure and/or displacement measurements in real time, and evaluating the full stress and deformation fields in the body of the structure, as well as predicting the location of the phreatic surface. Such model can be used for the detection hazardous pressure-stress states, for gaining insights in the most critical potential failure mechanisms, but also for the optimal design of the sensor network and the overall optimization of the monitoring system.POD-based model reduction, combined with Discrete Empirical Interpolation (DEIM) is used to tackle the coupled hydro-mechanical, non-linear, transient problem. The model is implemented in the FEniCS computing platform, an open-source platform that automates the solution of Partial Differential Equations with FEM. It is used for data assimilation applications, parameter identification (soil mechanical and hydraulic properties) and optimal sensor placement. The efficiency gains in inverse problem solving and the accuracy of the resulting ROM are examined and discussed., info:eu-repo/semantics/inPress

The permeability of rocks has a critical influence on their fluid transport response in critical geo-environmental applications, such as pollutant transport or underground storage of hazardous nuclear waste. In such processes, the materials microstructure may be altered as a result of various stimuli, thereby impacting the fluid transfer properties. Stress or strain state modifications are one of the main causes for such evolutions. To numerically address this concern, an integrated and automated numerical tool was developed and illustrated on subsets of microCT scans of a Vosges sandstone (i) to explore the links between the pore space properties and the corresponding macroscopic transfer properties, with (ii) an incorporation of the microstructural alterations associated with stress state variations by using a realistic image-based representation of the microstructural morphology. The ductile mechanical deformation behavior under high confining pressures at the scale of the microstructure, inducing pore closures by local plastifications, was modelled using finite elements simulations with a non-linear elastoplastic law, allowing to take into account the redistribution of local stresses. These simulations require robust discretization tools to capture the complex geometry of the porous network and the corresponding solid boundaries of the heterogeneous microstructural geometries. To achieve this, an integrated approach for the conformal discretization of complex implicit geometries based on signed distance fields was developed, producing high quality meshes from both imaging techniques and computational RVE generation methodologies. This conforming discretization approach was compared with an incompatible mode-based framework using a non conforming approach. This comparison highlighted the complementarity of both methods, the former capturing the effect of more detailed geometrical features, while the latter is more flexible as it allows using the same (non conform, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

In this work, a Representative Volume Element (RVE) generator based on the distance fields of arbitrary shaped inclusion packing is used to obtain morphologies of open-foam materials. When the inclusions are spherical, the tessellations of the resultant packing creates morphologies that are similar to physical foam samples in terms of their face-to-pore ratio, edge-to-face ratio and strut length distribution among others. Functions that combine the distance fields can be used to obtain the tessellations along with the necessary variations in the strut geometry and extract these open-foam morphologies. It is also possible to replace the inclusion packing with a predefined set of inclusions that are directly extracted from CT-scan based images.The use of discrete level-set functions results in steep discontinuities in the distance function derivatives. A multiple level-set based approach is presented that can appropriately capture the sharp edges of the open-foam struts from the resultant distance fields. Such an approach can circumvent the discontinuities presented by the distance fields which might lead to spurious stress concentrations in a material behavior analysis.The individual cells are then extracted as inclusion surfaces based on said combinations of the distance functions and their modifications. These surfaces can be joined together to obtain the final geometry of the open-foam morphologies. The physical attributes of the extracted geometries are compared to the experimental data. A statistical comparison is presented outlining the various features. The study is extended to morphologies that have been extracted using CT-scan images. With the help of mesh optimization tools, surface triangulations can be obtained, merged and developed as finite element (FE) models. The models are ready to use in a multi-scale study to obtain the homogenized material behavior. The upscaling can help assess the practical applications of these models by comparing with experime, Dans ce travail, un générateur de volumes élémentaires représentatifs (VER) basé sur les champs de distance d'un agrégat d'inclusions de forme arbitraire est développé dans le cadre de matériaux moussés à structure ouverte. Lorsque les inclusions sont sphériques, la tessellation de l'agrégat résulte en des morphologies similaires aux échantillons de mousse physique en termes de rapports des nombres de face par pores et de bords par faces, ainsi que de la distribution de la longueur des entretoises, entre autres. Les fonctions qui combinent les champs de distance peuvent être utilisées pour obtenir des tesselations avec les variations nécessaires aux géométries des entretoises et extraire ces morphologies de mousse ouverte. Il est également possible de remplacer l'agrégat d'inclusions par un ensemble prédéfini d'inclusions qui sont directement extraites d'images tomographiques.L'utilisation de fonctions de niveaux discrètes entraîne de fortes discontinuités dans les dérivées des champs de distance. Une approche basée sur des ensembles de niveaux multiples est présentée qui peut capturer de manière appropriée les arêtes vives des entretoises des mousses ouvertes à partir des champs de distance résultants. Une telle approche peut contourner les discontinuités présentées par les champs de distance qui pourraient conduire à des concentrations de contraintes parasites dans une analyse ducomportement des matériaux.Les pores individuels sont ensuite extraits en tant que surfaces d'inclusions sur la base desdites combinaisons des fonctions de distance et de leurs modifications. Ces surfaces peuvent être réunies pour obtenir la géométrie finale des morphologies de mousse ouverte. Les attributs physiques des géométries extraites sont comparés aux données expérimentales. Une comparaison statistique est présentée décrivant les différentes caractéristiques. L'étude est étendue aux morphologies qui ont été extraites à l'aide d'images tomographiques.À l'aide d'outils d'optimisation, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

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Clay soils can be stabilized by the chemical reaction between the clay particles and lime to produce calcium aluminate and calcium silicate minerals. This cementation effect on clay particles result in increasing the strength of lime-treated clay soils. The mechanical strengths (compressive, tensile and shear strengths) of clay soils are improved from soft to stiff behavior by treating with lime and evolve along the curing time.An extensive experimental investigation has been carried out using laboratory reconstituted (compacted) expansive soils, covering a range of plasticity indices. Four selected soils with different fundamental physical and mechanical behaviors have been used to stabilize with lime. In addition to basic geomechanical characterization tests (modified proctor compaction, uniaxial compression strength, indirect tensile strength, oedometric compression, direct shear tests), a special focus was put on triaxial compression and extension tests upon drained and undrained conditions. Also, the development of swelling pressure upon wetting was also carefully investigated.The shear behavior of compacted clay soils is experimentally investigated by using both direct shear test and triaxial shear tests. These tests were conducted on saturated specimens for four selected soils. It is observed that the shear strength of both tests is evolving with addition of lime and with the plasticity index. In addition to the strength parameters, triaxial shear test was also used to determine the Young modulus of treated soils. It was noticed that the lime treatment increases the elastic modulus of selected clay soils.The triaxial compression system was modified to a triaxial extension system in order to evaluate the triaxial tensile strength of one of the tested soils (N1, from Quenast, Belgium). The pure tensile strength of soils can be determined from triaxial extension test at low confining pressures while high confining pressures induces shear failure.The failure crit, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

The mechanical behavior of closed cell metallic foams strongly depends on their geometry at the scale of cells and cell walls. Two approaches are proposed in this work to address this computationally:(i) a controlled geometrical description of foam morphology features by exploiting an advanced tessellation-based procedure, allowing to generate realistic microstructural geometry,(ii) a procedure allowing to extract geometrical features of a foam morphology based on image-based modelling using CT scans. The first approach proposes a methodology that allows the automated generation of RVEs with a detailed control of the microstructure, including of cell geometries. It is primarily based on an inclusions packing algorithm assisted by distance fields control. Such distance fields can subsequently be used to morph inclusions, producing generalized tessellations with the possibility of incorporating curved and irregular boundaries. 3D morphologies of closed cell foams are produced by extracting the geometry from a proper combination of distance field functions. The procedure allows controlling the cell size distribution, spatial cell wall thickness distribution (correlated or not with the cell size distribution), wall curvatures and/or defects. An automated 3D meshing tool for implicit geometries was exploited to produce high quality tetrahedral meshes from the generated implicit foam geometries. Representative volume element based simulations were performed using this approach to assess the different morphological features relative importance on the mechanical behaviour of ALPORAS. An original extension of this tool was incorporating the transformation of 3D geometry into a shell-based finite element model. This resulted in a significant gain in computation time and allowed for simulating compression test up to densification (being out of reach with 3D solid finite element models) showing a good qualitative match with experimental results from the literature.The second ap, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

This contribution presents an assessment of computational techniques enabling automated simulations of complex porous rocks microstructures based on 3D imaging techniques. A subset of a CT-scanned sandstone sample is used to compare the results obtained by two advanced discretization frameworks. Raw scan results are processed by a level-set-based segmentation technique to produce smooth geometries prone to finite element discretizations. A recently developed technique is outlined for conforming mesh generation for complex porous geometries described implicitly by functions. This allows generating high-quality tetrahedral meshes with selective refinement. Next to this, a technique that uses a kinematic enrichment by incompatible modes to represent the heterogeneous geometry is explained. Both techniques use the same implicit geometry as main input for the simulations. Mechanical simulations are conducted on a subset of a scanned sample of a sandstone under triaxial loading conditions for isotropic compressive loading and for loading conditions involving a stress deviator. The results are compared and discussed based on local stress distributions and on a Mohr–Coulomb criterion with tensile cut-off. The results show that both discretization strategies yield complementary tools and allow envisioning automated simulations based on raw CT scan data for porous rocks exhibiting complex pore space morphologies., SCOPUS: ar.j, info:eu-repo/semantics/published

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This work aims at investigating the adequacy of microstructurally based effective stress to predict the shear strength of unsaturated soils over a wide range of suction. For that purpose, shear strength data are acquired on a silty clay soil through two types of unsaturated triaxial tests: suction controlled triaxial tests and unconsolidated triaxial tests at constant water content. The microstructure of the soil is determined with Mercury Intrusion Porosimetry and is directly used in different expressions of microstructurally based effective stresses available in the literature. The large range of suction tested allows to determine the most consistent expression of the effective stress to reproduce the experimental observations., SCOPUS: cp.p, info:eu-repo/semantics/published

Many experimental evidences suggest that desiccation cracks in clay initiate as a result of the mobilization of soil tensile strength. However this mechanical approach disregards the cohesionless and effective stress-dependent behaviour of fine-grained soil. On the other hand recent findings in the literature suggest that effective stress-dependent shear failure criteria would be appropriate to explain the mechanisms of desiccation cracking for tensile total stress states. This work aims at assessing the validity of a shear failure criterion to predict the onset of cracking in clay forms exposed to air drying. Clay forms of various geometries were experimentally subjected to non-uniform hydraulic and mechanical boundary conditions. Time and location for crack initiation are monitored using a digital camera. Cracking experiments are then modelled in a hydro-mechanical framework using an effective-stress shear failure criterion. The comparison of simulations with experimental results for both the time and the location of cracking allows assuming that cracking occurs due to failure in shearing., SCOPUS: cp.p, info:eu-repo/semantics/published

The Boom Clay is considered as one of the potential host rock formation in Belgium for radioactive waste repository in deep geological layers. Gallery excavations will induce large hydro-mechanical disturbances around disposal system that need to be well understood and characterised. This study discusses particularly the role of interactions between the lining of the galleries and the host formation in the numerical characterisation of excavations in Boom Clay. The excavation and the convergence of the connecting gallery of the HADES underground research facility in Mol is modelled in a hydro-mechanical framework. Zero-thickness interface elements are used to manage numerically the contact between the host rock and the lining. Numerical predictions are compared with strains measurements recorded within the concrete segments of the lining in the underground research laboratory in Mol. The study highlights the impact of the anisotropic behavior of the host rock on the response of the model., SCOPUS: cp.k, info:eu-repo/semantics/published

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3D reinforced composites are favored for aerospace, automotive and wind turbine applicationbecause of their high specific stiffness and strength in the in-plane and out-ofplanedirections. In these composites, pins, stitching yarns and binder yarns are insertedthrough-the-thickness of the in-plane fiber-reinforced regions. Binder parameters as diameter,content, pattern and tensioning can further be varied to regulate the out-of-planeproperties. However, the insertion of these binders distorts the reinforcement which furthercan affect the global and local mechanical behaviour. Unit-cell models offered avaluable approach to assess the effect of the distortions on these mechanical features.An approach is presented to include the main geometrical features of pinned, stitchedand 3D woven composites into mesoscopic unit-cell models. Discretised lines, whichrepresent the main geometrical features, are hereby gradually shaped by geometrical operationswhile a geometrical contact treatment account for line interactions. The localfiber volume fraction and fiber direction distributions are afterwards modelled on crosssectionsin a post-processing step. Tools are further proposed to automatically transformthe geometrical models into finite element models. The effect of distortions, local fibervolume fraction and fiber direction, and typical geometrical features for each 3D reinforcedcomposite, on the stiffness and damage initiation stress levels is investigated bymeans of elastic finite element (FE)-computations.The shape of geometrical features corresponding to the different binder parameters couldautomatically be generated and the dimensions of features could be controlled by the parametersof the geometrical operations. The stiffness of a 3D reinforced composite havebeen observed to be either decreased or increased (dependent on the stacking sequence,the binder type and the loading direction). Early damage initiation in the FE-modelswas observed to take place near the binder loc, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

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Dans le but de comprendre les effets de l’infiltration et de l’évaporation sur la stabilité des pentes en conditions non saturées, des outils expérimentaux et de modélisation ont été développés puis appliqués au site de glissement de Gasekebuye au Burundi. La méthodologie adoptée pour arriver à cet objectif se base sur l’approche du problème de la stabilité des pentes comme une question de la résistance au cisaillement des sols. La résistance au cisaillement des sols dépendant de la distribution des pressions de pores dans le massif, il est alors important de comprendre comment l’infiltration et l’évaporation de l’eau dans les sols affectent ces pressions de pores.D’abord, un modèle de résistance au cisaillement en conditions non-saturées est formulé. Ainsi, une technique d’essais triaxiaux à succion contrôlée par translation d’axes est développée. Cette technique est très précise, mais elle ne permet pas d’imposer de grandes valeurs de succion. Ainsi, deux autres techniques sont utilisées pour atteindre de grandes valeurs de succion :les essais triaxiaux après compactage et les essais triaxiaux après séchage des échantillons de sol via des solutions salines. Les résultats obtenus ont permis de formuler un modèle de résistance au cisaillement valable pour une grande gamme de succion et basé sur la définition d’une contrainte effective appropriée.Ensuite, un modèle d’évaporation est formulé. Un tel modèle nécessite de réaliser des essais de séchage dans des conditions atmosphériques bien contrôlées. Ainsi, un dispositif de séchage des échantillons de sol où l’humidité relative est contrôlée via les solutions salines saturées a été développé et testé. La question des dimensions de l’échantillon à tester pour que les mécanismes d’évaporation observés au laboratoire soient similaires à ceux observés sur le terrain a été investiguée. Ainsi, l’analyse des mécanismes d’évaporation a permis de proposer des dimensions optimales des échantillons à tester qui permettraient de, In order to understand the impact of infiltration and evaporation on the stability of soil slope in unsaturated conditions, experimental and modeling tools have been developed and applied to a landslide site located at Gasekebuye in Burundi. The methodology adopted to achieve this goal is based on the understanding of the slope stability issue as a problem of soil shear strength. As soil shear strength depends on the distribution of pore water pressures in the ground, it is important to investigate how infiltration and evaporation of water in soils affect these pore water pressures.First an unified model of shear strength under unsaturated conditions is formulated. Thus a technique of triaxial tests where suction is controlled by translation axis method is developed. This technique is accurate, but does not allow to impose large suction values. So, two other techniques are used to impose high suction values: triaxial tests at fixed water content after soil compaction and after drying controlled by the saline solutions technique. The results allow us formulating an unified shear resistance model for a large suction range and based on the concept of effective stress.Then an evaporation model is formulated. Such a model requires performing drying tests under well controlled atmospheric conditions. Thus a set-up for the drying of the soil samples where the relative humidity is controlled with saturated saline solutions has been developed and tested. The impact of the dimensions of the sample on the kinetics and the mechanisms of evaporation is investigated. The analysis of the evaporation mechanisms allows us to propose optimal dimensions of tested samples in order to reproduce in the lab the same drying mechanisms as observed in the field. These samples are then dried to study the influence of the air relative humidity on the evaporation kinetics. Other tests are also performed in a convective dryer where the air velocity is controlled. The results at different relativ, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

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Rammed earth constructions exhibit strength and deformation properties that evolve as a function of the relative humidity of the air in contact with the walls. This effect must be considered in the structural design of the construction. This work studies, through finite element simulation, the impact of the hygroscopic transfers through the wall on the structural response of a classical two-storey rammed earth building. The coupling between the mechanical and the hygroscopic behaviour is considered by the concept of effective stress for unsaturated soils, in order to reproduce the effect of suction on the strength, the stiffness and the volumetric variations of the rammed earth. The simulations show classical deformation of the structure due to distributed load on the floors while the hygroscopic changes in the rammed earth (essentially drying) induce additional displacements of the walls that remain in a very acceptable range. Finally, an extreme case is envisaged in which the loads on the floors are increased excessively in order to study the plastic response of the wall., SCOPUS: ar.j, info:eu-repo/semantics/published

ERS, ENVISAT and TerraSAR-X Synthetic Aperture Radar scenes covering the time span 1992–2014 were processed using a Persistent Scatterer technique to study the ground movements in Merchtem (25 km NW of Brussels, Belgium). The processed datasets, covering three consecutive time intervals, reveal that the investigated area is affected by a global subsidence trend related to the extraction of groundwater in the deeper Cambro-Silurian aquifer. Through time the subsidence pattern is reduced and replaced by an uplift related to the rising water table attested by piezometers located in this aquifer. The subsidence is finally reduced to a zone where currently three breweries are very active and pump groundwater in the Ledo-Paniselian aquifer and in the Cambro-Silurian for process water for the production., SCOPUS: ar.j, info:eu-repo/semantics/published