Yes / Because of the recent worldwide construction expansion, new roads and buildings may be constructed over already existing buried infrastructures e.g. buried utility pipes, leading to excessive loads threatening their stability and longevity. Limited research studies are available to assess the effect of geogrid reinforcing layers inclusion on mitigating the additional stresses on buried structures due to cyclic loadings. In this research, large-scale fully instrumented laboratory tests were conducted to investigate the behaviour of flexible High-Density Polyethylene pipes (HDPE), in unreinforced and geogrid-reinforced sand, subjected to incrementally increasing cyclic loading, e.g. due to different vehicles capacities or load increase with passing time. Results illustrated that deformation rate in pipe and footing, strain generation rate in pipe and reinforcing layers are rapidly increased in the initial loading cycles, in particular during the first 300 cycles, and then the rate of change decreases significantly, as more cycles are applied. In the unreinforced case, increasing the pipe burial depth significantly reduced the generated deformation and strain in the pipe; however, it has a situational effect on the footing settlement, where it increased after pipe burial depth to its diameter ratio (H/D) of 2.5. In reinforced cases, deformation and strain significantly reduced with the increase in pipe burial depth and number of reinforcing layers. Measurement of strain illustrated that strain generated in the lower reinforcing layer is always higher than that recorded in the upper one, regardless pipe burial depth and value of applied load.

Yes / Reinforced piled embankment technique is becoming increasingly utilised for the construction over soft grounds due to its efficiency on reducing potential settlement, speed of construction and associated cost. Most of previous studies focused on developing understanding for the behaviour of thick embankments that are loaded with a static surcharge load. Data for the behaviour of shallow piled embankments under cyclic loadings are scarce. In this study, an experimental programme was undertaken using a fully instrumented testing rig to generate data and improve our understanding for the behaviour of unreinforced and reinforced shallow piled embankments subject to monotonic and cyclic loadings that were applied over a predetermined area of the embankment. The experimental results showed that collapse of soil arching is imminent and occurs during the first few cycles of load. However, regain of strength and recovery of the arching effect was observable during further stages of cyclic loadings due to densification of the embankment material and deformation of the soft subsoil. Inclusion of reinforcement layers was found to enhance the performance of load transfer mechanisms by concentrating stresses on pile caps. The results clearly showed a significant reduction in surface settlement, soft subsoil settlement and heaving with increasing the number of reinforcement layers.

The embedment behavior of dowels in timber structures, as an essential parameter in the design of connections, is the subject of this thesis. There are numerous advantages using timber structures, including sustainability, energy efficiency, and aesthetic appeal. The mechanical performance of connections in timber structures can be affected by environmental variables, such as moisture content. Thus, in the thesis the embedment behavior of dowels in timber, including the embedment strength and elastic and plastic stiffness at various moisture levels was investigated. In addition to different moisture contents, the effects coming along with changing the moisture content, like swelling and shrinkage, in combination with the assembly history were studied. The study investigated the effects of moisture content variations on the embedment behavior of dowels in timber loaded perpendicular to the grain at relative humidity levels of 38%, 65%, and 85% at a temperature of 20◦C. The study also explored the impact of assembly history of the steel dowels on the embedment behavior. The expression ”assembly history” refers the effects of drilling and assembling steel dowels at different times, i.e. if drilling the timber occurs before changing the moisture content or after changing the moisture content.  Full-hole embedment tests were conducted in five different series to cover all three levels of moisture content while taking the assembly history into account. In total, 100 embedment experiments were carried out, with 50 samples of spruce and 50 samples of birch being assessed perpendicular to the grain. In addition, 20 solid timber specimens were exposed to cyclic loading to evaluate the embedment behavior under these conditions. To evaluate the stress on the timber around the dowel, finite-element simulations, using linear-elastic material behavior in combination with volumetric changes due to moisture variation were conducted. Corresponding to the assembly history in the experiments, the situations of moisture variation in presence and absence of the steel dowel for the swelling and shrinkage case were investigated. The experimental results showed that while the elastic and plastic embedment stiffness can be impacted by moisture content only in low MC situations, it can potentially affect embedment strength in both dry and wet conditions. Additionally, the assembly history influences only the plastic stiffness in a low MC condition. Results from cyclic loading have shown no significant difference to embedment strength and stiffness gained from monotonic loading. According to numerical simulations, the tensile normal stress in the direction perpendicular to the load direction is higher than the tension strength for the shrinkage case with the dowel present. This might be explained by using a simple linear elastic material model in the FEM simulation, which causes an overestimation in the stiffness properties. In conclusion, this thesis offers new perspectives and a deeper knowledge of how moisture content, assembly history, and cyclic loading perpendicular to the grain affect the embedment behavior of dowels in timber connections.

No description available.

Energy piles are deep foundation elements designed to utilize near-surface geothermal energy, while at the same time serve as foundations for buildings. The use of energy piles for geothermal heat exchange has been steadily increasing during the last decade, yet there are still pending questions on their thermo-mechanical behavior. The change in temperature along energy piles, resulting from their employment in heat exchange operations, causes axial displacements, thermally induced axial stresses and changes in mobilized shaft resistance which may have possible effects on their behavior. In order to investigate these effects, an extensive field test program, including conventional pile load tests and application of heating-cooling cycles was conducted on three energy piles during a period of six weeks. Temperature changes were applied to the test piles with and without maintained mechanical loads to investigate the effects of structural loads on energy piles. Moreover, the lengths of the test piles were determined to represent different end-restraining conditions at the toe. Various sensors were installed to monitor the strain and temperature changes along the test piles. Axial stress and shaft resistance profiles inferred from the field test data along with the driven conclusions are presented herein for all three test piles. It is inferred from the field test results that changes in temperature results in thermally induced compressive or tensile axial stresses along energy piles, the magnitude of which increases with higher restrictions such as structural load on top or higher toe resistance. Moreover, lower change in shaft resistance is observed with increasing restrictions along the energy piles. In addition to the design, deployment, and execution of the field test, a thermo-mechanical cyclic numerical model was developed as a part of this research. In this numerical model, load-transfer approach was coupled with the Masing's Rule in order to simulate the two-way cyclic axial displacement of energy piles during temperature changes. The numerical model was validated using the field test results for cyclic thermal load and thermo-mechanical load applications. It is concluded that the use of load-transfer approach coupled with the Masing's Rule is capable of simulating the cyclic thermo-mechanical behavior of energy piles. / Ph. D.

Yes / Three-dimensional finite element models were executed and validated to investigate the performance of buried flexible high-density Polyethylene (HDPE) pipes, in unreinforced and multi-geogrid-reinforced sand beds, while varying pipe burial depth, number of geogrid-layers, and magnitude of applied cyclic loading. Geogrid-layers were simulated considering their geometrical thickness and apertures, where an elasto-plastic constitutive model represented its behaviour. Soil-geogrid load transfer mechanisms due to interlocked soil in-between the apertures of the geogrid-layer were modelled. In unreinforced and reinforced cases, pipe burial depth increase contributed to decreasing deformations of the footing and pipe, and the crown pressure until reaching an optimum value of pipe burial depth. On the contrary, the geogrid-layers strain increased with increasing pipe burial depth. A flexible slab was formed due to the inclusion of two-geogrid-layers, leading to an increase in the strain in the lower geogrid-layer, despite its lower deformation. Inclusion of more than two geogrid-layers formed a heavily reinforced system of higher stiffness, and consequently, strain distribution in the geogrid-layers varied, where the upper layer experienced the maximum strain. In heavily reinforced systems, increasing the amplitude of cyclic loading resulted in a strain redistribution process in the reinforced zone, where the second layer experienced the maximum strain.

Yes / In this study, large-scale fully instrumented laboratory tests were conducted to investigate the behaviour of buried flexible high-density polyethylene (HDPE) pipes, in sand beds with and without voids subjected to incrementally increasing cyclic loading. Voids with a predetermined size were created at one side of the springlines of the pipes, which were buried at variable depths, H, of 1.5, 2.0 and 2.5 times the diameter of the pipe, D. Results showed that increasing the pipe burial depth, H/D, contributed to decreasing the settlement of the footing, deformation of the pipe crown and invert, lateral displacement of the spring-line, and the stress and strain generated along the pipe crown and invert. Void presence led to a significant increase in the footing settlement, which ranged from 3 % up to 18 %, according to H/D. Furthermore, void presence led to a sharp increase in the crown, invert, and spring-line settlements, which ranged from 34 % to 52 %, 10 %–12.5 %, and 13 %–38 %, respectively. Increasing pipe burial depth was found to be highly effective in protecting buried pipes, minimising inevitable consequences of the presence of voids. However, this was combined with an increase in the pressure at the pipe spring-line that led to a positive horizontal support at the pipe’s spring-lines resulting in reducing pipe deformation.

L’ingénierie tissulaire vise à l’élaboration de prothèses biologiques par la régénération ou la culture, in vitro ou in vivo, de tissus ou d’organes. Dans la stratégie de culture in vitro, le développement de nouveaux outils, tels que des bioréacteurs, permettant la culture de cellules ou de tissus sous sollicitations mécaniques spécifiques au tissu est primordial. De plus, l’avancée de cette discipline dans la régénération des tissus nécessite de développer, dès à présent, des méthodes d’évaluation mécanique satisfaisantes permettant de comparer ces néo-tissus aux tissus sains selon des critères de sollicitations physiologiques. En effet, pour parvenir à une bonne évaluation de ces matériaux, il est nécessaire de pouvoir les tester sur des chargements représentatifs des sollicitations physiologiques auxquelles ils sont soumis. Nous avons ainsi, dans un premier temps, conçu et développé un bioréacteur de ligaments permettant la culture de cellules stimulées mécaniquement par des sollicitations cycliques de traction-torsion. Ce bioréacteur a été dimensionné afin de pouvoir obtenir des bio-prothèses de taille comparable aux ligaments et tendons à remplacer (4 à 5 cm de long). Nous avons, dans un deuxième temps, développé un modèle du comportement mécanique global de ces tissus à partir du formalisme thermodynamique développé au sein de notre laboratoire et des observations faites sur des tendons d’Achille de lapin. Ce modèle a pour but d’approfondir la compréhension des structures intervenant de façon prépondérante dans la qualité mécanique de ces tissus ainsi que l’évaluation et l’optimisation des matrices de support et des néo-tissus devant s’y substituer / Tissue Engineering aims to fabricate bio-prostheses by regenerating or culture, in vivo or in vitro, tissues or organs. In the in vitro strategy, developing new tools such as bioréactors which allow the culture of cells or tissues under their specific mechanical solicitations is a huge point. Moreover, the last advances of this discipline in regeneration of tissues require new mechanical model allowing their evaluation and comparison to native tissue under physiological loading. Indeed, in order to obtain a good evaluation of their mechanical quality, it is important to be able to applied mechanical solicitations linked to physiological ones. As a first step, a bioreactor of ligament allowing the culture of cells under mechanical solicitations of cyclic traction-torsion was designed and developed. This bioreactor was sized to potentially obtain a bio-prosthesis comparable to native tissue in term of size (4 to 5 cm long). In a second time, a mechanical model was elaborated based on a thermodynamic formalism developed in our laboratory and the observation made on rabbit Achilles tendons. The goals of this model are to improve our knowledge on the mayor structures involved into the mechanical quality of theses tissues and to evaluate and optimise the scaffolds and neo-tissues of substitution

La thèse vise à étudier le comportement mécanique des sables sous la condition de cisaillement simple et à son application au calcul des pieux. Tout d'abord, un modèle de sable récemment développé (SIMSAND) prenant en compte l'état critique est introduit avec une procédure directe de détermination des paramètres. Le modèle est implanté dans un code de calcul aux éléments finis qui a fait l’objet de différentes validations. Ensuite, le modèle est amélioré en considérant l'anisotropie inhérente lors de la rotation des contraintes principales sous la condition de cisaillement simple et a été validé en utilisant les résultats des essais tri axiaux et de cisaillement simple sur le sable de Fontainebleau. Les essais de cisaillement simple sont analysés en imposant les conditions de sollicitations réelles tridimensionnelles appliquées par l’appareillage utilisé. L'inhomogénéité de l'échantillon avec l'effet de la taille de l'échantillon est également étudiée. Puis, des essais de cisaillement simple cycliques drainés et non-drainés sur le sable de Fontainebleau sont effectués pour étudier les caractéristiques sous charges cycliques, telles que la dégradation de la contrainte normale effective et l'accumulation de la déformation volumique, compte tenus de certains facteurs comme l’indice des vide initial, la contrainte normale appliquée, le rapport de contrainte de cisaillement cyclique et le rapport de contrainte de cisaillement moyenne. Sur la base de ces résultats, deux modèles analytiques sont proposés pour prédire la dégradation à long terme de la contrainte normale effective et l'accumulation des déformations volumiques en fonction du nombre de cycles. En outre, les essais cycliques de cisaillement simple sont simulés par le modèle SIMSAND amélioré en utilisant une technique d'inversion de contrainte. Enfin, on simule une série de pieux modèles sous charges monotone et cyclique pour laquelle la résistance en pointe du pieu est évaluée ainsi que la réponse du sol entourant le pieu. / The thesis aims to study the mechanical behaviour of sand under simple shear condition and to apply the results to the numerical simulation of pile foundation. First, a recently developed critical state sand model (SIMSAND) is introduced with a straight forward procedure of parameters determination, implemented into a finite element code and then subjected to a series of validations. Then, the model is enhanced by considering the inherent anisotropy during the principal stress rotation under the simple shear condition and validated by using results of both triaxial tests and simple shear tests on Fontainebleau sand. Simple shear tests are analysed by simulating in three-dimensions the real conditions imposed by the simple shear apparatus. The inhomogeneity of the samples with the effect of sample size is also investigated. Furthermore, undrained and drained cyclic simple shear tests on Fontainebleau sand are conducted to investigate the cyclic responses, such as the effective normal stress degradation and the volumetric strain accumulation, respectively, considering some impact factors such as the initial void ratio, the normal stress, the cyclic shear stress ratio and the average shear stress ratio. Based on these results, two analytical models are proposed to predict the long-term degradation of the effective normal stress and the accumulation of the volumetric strain with the number of cycles. Moreover, the cyclic simple shear tests are simulated by the enhanced SIMSAND model by incorporating the stress reversal technique. Finally, a series of model pile tests under monotonic and cyclic loadings are simulated based on which the cone resistance of the piles is evaluated as well as the response of the soil surrounding the pile.

La capacité opérationnelle axiale en service de pieux battus reste une zone d'incertitude, en particulier pour les structures offshore. La recherche sur le terrain a montré que le frottement latéral peut augmenter au cours des mois ou des années après le battage. Si des tendances similaires se retrouvent dans des ouvrages offshore, les avantages en terme d'ingénierie de réalisation peuvent être très importants. D'autre part, les fondations sur pieux de plates-formes de gaz, de pétrole sont soumises à des chargements cycliques à long terme qui peuvent influencer leur capacité à l'arrachement. Les pieux battus en eau profonde connaissent un grand nombre de cycles complets de charge-décharge pouvant contribuer à la dégradation du frottement latéral lors de l'installation. Cette thèse vise à mieux comprendre les principaux résultats obtenus avec des pieux réels en sable siliceux, par le biais d'une recherche à échelle de laboratoire sous conditions environnementales contrôlées. Ce travail fait partie d'un programme de recherche commun entre le Laboratoire 3SR de Grenoble, l'Imperial College London, et le projet français de recherche ANR- SOLCYP. La réponse de l'interface sol-pieu lors de l'installation ainsi que les périodes de vieillissement et de chargements cycliques axiaux ont été étudiés au laboratoire en utilisant des pieux-modèles installés dans la chambre d'étalonnage de Grenoble. Plusieurs essais avec le pieu modèle Mini-ICP (instrumenté avec des capteurs de tension totale à la surface du pieu (SST) pour les mesures de contraintes radiales de cisaillement à 3 sections) ont permis l'analyse de chemin de contrainte locale à l'interface du pieu. Des capteurs miniatures ont en outre été installés dans le massif de sable pour une mesure de contrainte lors de l'installation du pieu et son chargement ultérieur. Les effets des méthodes d'installation, de la taille des particules de sable, ou de la saturation du sable et du chargement de l'environnement, ont été pris en compte pour le vieillissement de la capacité. Les évolutions locales de l'interface radiale et du cisaillement sont en accord avec les prédictions des méthodes de conception modernes basées sur le CPT. Des preuves d'effets d'échelle soulignent l'importance des conditions aux limites appliquées à la modélisation physique. Des séries d'essais non-alternés purement en traction, ainsi que des essais alternés ont été réalisés sous contrôle en charge ou en déplacement. Les mesures locales effectuées dans les chemins de contraintes effectives montrent une contraction radiale de la masse de sable au voisinage du pieu. Les incréments de l'amplitude de charge et du déplacement imposé accélèrent les taux de dégradation cyclique. Un nouveau diagramme de stabilité cyclique a été réalisé, en résumant les essais de chargement cycliques axiaux pour les pieux foncés et battus dans du sable siliceux moyennement dense. Des mécanismes complexes comme la rupture des grains et des changements de densité locale à l'interface du pieu peuvent affecter la réponse des pieux. La cinématique derrière leur installation et l'interaction avec le sol environnant reste encore très limitée. Comprendre comment un matériau granulaire interagit avec le pieu est important pour étudier la réponse globale du pieu. Les observations globales du comportement des pieux dans la chambre d'étalonnage ont été modélisées à une échelle micro en utilisant la tomographie aux rayons X du Laboratoire 3SR à Grenoble. Le programme expérimental comprenait des essais sur une chambre d'étalonnage modèle afin d'analyser le champ de déplacement lors de l'installation d'un pieu modèle, à l'aide des techniques de corrélation d'images (DIC) en trois dimensions. Des analyses micromécaniques d'échantillons «intacts» récupérés post mortem à l'interface du pieu ont été également effectuées pour mettre en évidence de possibles changements radiaux de densité ainsi que la rupture des grains. / The operational in-service axial capacity of driven piles remains an area of uncertainty, especially for offshore structures. Field research has demonstrated that axial shaft capacities may increase over the months or years after driving. If similar trends apply offshore, the realisable engineering benefits are very significant. On the other hand, the piled foundations of oil/gas platforms and wind/water turbines are subject to long term environmental and in service cyclic loading due for example to waves, vibrations and storms that may also affect their shaft capacity. Deep driven piles experience large numbers of full load-unload cycles that contribute to shaft capacity degradation during installation. This thesis aims to improve understanding of the main results obtained with full-scale piles in silica sand through a laboratory scale investigation performed under controlled environmental conditions. This work was part of a joint research programme between the Grenoble Laboratory 3SR and Imperial College London, and the French National SOLCYP research project. The response of the soil-pile interface during installation, ageing periods and cyclic loading tests have been studied using laboratory model piles installed in the large Grenoble Calibration Chamber. Several tests with the Mini-ICP pile allow the analyses of local stress path at the pile's interface. This model pile is instrumented with surface stress transducers (SST) for local measurements of total and radial shear stresses at 3 different sections along the pile's shaft. In addition, miniature soil stress transducers were installed into the sand mass for total stress measurements during pile installation and loading. Possible ageing effects as installation methods, sand particle size, sand saturation and environmental loading were studied. Local evolution of interface radial and shear stresses agree with predictions from modern CPT based design methods. Evidence of possible scale effects remark the importance of the boundary conditions applied in physical modelling. Series of one-way purely tensile and two-way axial cyclic loading tests were performed under load and displacement control. Local measurements made of the effective stress paths shows radial contraction of the sand mass in the vicinity of the pile. Increments in loading amplitude and imposed displacements accelerate cyclic degradation rates. A new interactive shaft stability chart was produced as a summary of axial cyclic loading tests for both jacked and driven piles in medium dense silica sand. Laboratory tests confirm findings from field tests where one-way low amplitude cycles lead to beneficial increases in tensile pile capacity of up to 20%. Complex mechanisms as grain breakage and local density changes at the pile's interface. The kinematics behind the installation of piles and its interaction with the surrounding soil is still limited. Understanding how granular material interacts with the pile may reveal important to understand the global pile response. The global observations of the pile behaviour from calibration chamber tests were modelled at a micro scale using Micro Computed Tomography at the Grenoble Laboratory 3SR. The experimental campaign included tests on a model calibration chamber devoted to the displacement field analyses during the installation of a model piles using three dimensional (3D) digital image correlation (DIC). Micromechanical analysis of « intact » post-mortem samples recovered at the pille's interface were also conducted for evidences of radial density gradient and grain breakage.