Caractérisations physico-mécaniques de sciages de 1er choix en vue d'applications structurelles

National audienceLe matériau bois présente une grande variabilité de ses propriétés mécaniques. Lacaractérisation de la résistance à rupture d'une essence sur de multiples essais permetl'identification d'une distribution des mesures souvent proche d'une loi normale. Les normeseuropéennes de construction (Eurocodes) fixent la valeur de résistance au fractile à 5 %inférieur comme valeur caractéristique de résistance. Cette résistance est suffisante pour desusages bas de gamme en charpente. Cependant les 5% au-dessus du fractile supérieur sontnettement sous valorisés. Il s’agit de pièces de bois quasiment sans défauts facilementdétectables par les outils actuels de production industrielle, et possédant des propriétésmécaniques très proches de celles du bois dit parfait.Un des enjeux pour l’avenir est donc de trier, qualifier et tracer ces sciages de bois de hautequalité pour valoriser la ressource dans des usages à hautes performances structurelles. Plusparticulièrement les essences de pins sont sous utilisées dans la conception d'élémentsstructurels malgré une ressource forestière abondante. La démarche mise en oeuvre au coursde cette thèse permettra de répondre à cet objectif sur différentes essences de pin pouraméliorer la valeur ajoutée produite, grâce à de nouveaux usages

Quantification of Neural Network Uncertainties on the Hydrogeological Predictions by Probability Density Functions

International audienceThe risk of drought impacting the drinking water and agricultural production is worrying in the developed countries, especially in a changing climate context. To manage and prevent this phenomenon, real-time monitoring and predictive systems are emerging as the key solutions. In the field of artificial intelligence, neural networks are one of these predictive systems. This family of parameterized models is a composition of neuronal functions, which apply a non-linear transformation from their inputs to their outputs. These networks are able to learn a hydro(geo)logical system behaviour using a database composed of observed inputs (rainfall, evapotranspiration, etc.) and outputs (groundwater level, discharge, etc.), thanks to an algorithm minimizing a cost function between observed and simulated outputs. However, it remains difficult to assess the uncertainty generated by these models, possibly leading to misinterpretations by the end users. These uncertainties are mainly of three types. The first is related to the input data. Indeed, hydrosystems are surface elements whereas meteorological inputs are punctual elements. The interpolation error can, therefore, be significant because of the lack of knowledge between gauging stations. The second is the neural network model architecture itself. It is possible to deal with this source of uncertainty using regularization methods. Finally, the neural networks are submitted to uncertainties related to parameter initialization, before the training step. The initial parameters may have an important impact on the results. In this paper, we address the prediction of the Blavet groundwater level (Bretagne, France). In order to assess uncertainties, we will first focus on the parameters initialization of the model. Neuronal models are optimized using cross-validation and early stopping. Then, an ensemble model is realized, in which each member is the result of a unique set of parameters initialization. The purpose of the study is to define how many initializations are necessary to obtain a reasonable confidence interval for forecasts, with the smallest interval and the higher rate of observed points inside this interval. The best model will be determined using cross-validation scores thereby ensuring optimal robustness. We show that, in this case study, an ensemble model of 20 different initializations is sufficient to estimate uncertainty while preserving quality. In the second part, the resulting ensemble model will be used to estimate the global model uncertainty using probability density functions (pdf) applied to the distribution of groundwater level data and cross-validation scores of forecasts. It reveals that the groundwater level predictions are composed of two mixed distributions. Therefore, we will use the expectation-maximization algorithm (EM) to obtain parameters of mixed models. Mixed normal and mixed Gumbel laws, among five mixed distributions assessed, give the best groundwater distribution and are able to generate an abacus drawing uncertainty of mode

Influence of growth parameters on mountain pine wood properties

International audienceMountain pine (Pinus uncinata Ramon ex DC) is an important forest species in the Pyrenean Mountain, both in France and Spain [1]. In a project dealing with its use as timber [2], physical and mechanical tests were performed on clear wood specimen.Wood properties are determined both by genetics (species and provenance) and by growth adaptation to the tree's environnement through variations in ring width (RW), basic density (BD), microfibril angle (MFA) and chemical composition of the cell wall matrix. The square of sound speed called here specific modulus (SM) is a good proxy for MFA [3] and fibre saturation point (FSP) can be a proxy of chemical composition of the cell wall.Shrinkage parameters: total radial (RS), tangential (TS), volumetric (VS) as well as shrinkage anisotropy (SA=TS/RS) are important physical properties for timber use. Longitudinal modulus of elasticity (MOE), resistance to compression (CS) and deformability (strain limit before damage beginning in compression) are key mechanical properties both for tree mechanics and timber technology.All these properties are known to vary, even in a given species, often up to two or threefold, mostly due to adaptation to growth condition, and this is a drawback for timber use. This presentation will focus on the links between variations of growth parameters and wood properties with the objective to build regression models of properties

Spatial analysis of hydraulic conductivity for slope deposits at catchment scale in Northern Tuscany, Italy

Hydraulic conductivity (K) is a relevant engineering geology property of slope deposits (SD) overlying the geological bedrock. This parameter is relevant at the field scale to simulate infiltration and runoff processes, hillslope stability numerical analysis, hydrological studies and environmental issues. Direct measurements (field and laboratory tests), as well as indirect estimations (e:g. correlations from grain size distribution, pedotransfer functions) are available in the literature for estimating K. Many measurements are required to obtain significant results since K depends on many factors such as grain size distribution, bulk density, organic matter, etc. A big set (about 750) of K field measurements in the vadose zone of SD in Northern Tuscany (Italy) has been performed by means of constant and/or falling head permeameter. For each test site (a total of 150 locations), other engineering geology properties of SD such as depth, texture, bulk density, Atterberg limits and grain size distribution have been determined. In this work the local variability of K has been estimated thanks to a statistical analysis of K for each test site. Moreover geostatistical techniques have been applied to infer the spatial correlation of K at the catchment scale. The results show that K varies across the SD profile and in the geographic neighborhood of the test site exhibiting high spatial variability within the study area. The new pedotransfer function, that has been developed with satisfactory results (the determination coefficient R2 = 0.84), suggests that the depth of SD and d20 (is the diameter corresponding to 20% finer in the particle-size distribution) play a relevant role in the prediction of K:These parameters can be considered with profit in spatial analysis of K for SD allowing to produce K maps in the study area

Application combinée de l’analyse structurale, de la géostatistique et de la théorie des blocs clés à l’étude des problèmes de stabilité et de confortement des travaux miniers

International audienceThe study presented in this paper aims at the setting up of a methodology which allows the design of mining works, underground or otherwise, taking into account the geological structure of rock masses in which they are located. Three stages of this methodology are presented: the determination of statistical and geostatistical characteristics of the population of fractures; the generation of a field of fractures, with given statistical characteristics, by simulation; the study of the stability of isolated blocks defined by these fractures, by means of the key-block theory. Following the processing of this structural data, rules of action, concerning the conception and execution of the planned structure, will be drawn up.L'étude présentée ici vise la mise en place d'une méthodologie qui permette le dimensionnement d'ouvrages miniers, souterrains ou non, en fonction de la structure géologique du massif rocheux dans lequel ils se trouvent.Trois étapes de cette méthodologie sont exposées sucessivement : – la détermination des caractéristiques statistiques et géostatistiques des populations de fractures ; – la génération, par simulation, d'un champ de fractures de caractéristiques statistiques données ; – l’étude de la stabilité de blocs isolés, définis par ces fractures ; ceci grâce à la théorie des blocs clés.A la suite de cette chaîne de traitement des données structurales, des règles d’action devront être tirées, concernant la conception et l'exécution des ouvrages à réaliser

Modélisation du comportement mécanique par éléments discrets d'ouvrages tri-dimensionnels. Contribution à la définition d'éléments de contacts surfaciques

Cette thèse concerne la modélisation d'ouvrages maçonnés tri-dimensionnels en grand appareil, précontraints, ou comportant un grand nombre de blocs. Ces structures sont des constructions en gros blocs de pierre, éventuellement liés par des joints de mortier, dont les géométries tridimensionnelles ne permettent généralement pas la définition d'un volume élémentaire représentatif. Le comportement mécanique de ces édifices ou structures, peut être étudié par des méthodes qui considèrent le comportement des blocs et leurs interactions avec des blocs voisins par frottement sec ou en présence de mortier cohésif. Nous avons donc choisi de les modéliser par la méthode des éléments discrets Non Smooth Contact Dynamics. Les monuments étudiés sont des structures en pierres massives, simple appareil régulier (mur) ou irrégulier (pont Julien) et structures précontraintes (escalier, coupole). D'une part, un nouvel algorithme de détection des contacts a été développé pour gérer les contacts surfaciques, spécifiques aux maçonneries. Diverses applications sur des cas réels, et des comparaisons avec des expériences issues de la littérature, ont montré la robustesse de l'algorithme. Les résultats obtenus par l'analyse des descentes de charges sont cohérents avec les caractères physiques et géométriques des ouvrages considérés. D'autre part, les liaisons de contacts conduisent souvent à un problème statiquement indéterminé au niveau local. L'étude sur des cas académiques a permis de tester la pertinence de la méthode. Une comparaison a été faite avec la méthode de résolution existante, implémentée dans LMGC90MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Contribution à l étude de la stabilité des massifs rocheux fracturés (caractérisation de la fracturation in situ, géostatistique et mécanique des milieux discrets)

La simulation numérique est un outil essentiel pour mieux comprendre la réalité des phénomènes qui se produisent au sein des milieux discrets, en particulier des milieux rocheux fracturés. Notre travail a pour objectif d étudier le comportement mécanique et dynamique des milieux rocheux en réalisant des modèles discontinus dans lesquels les mesures de l orientation et l espacement interfractura, effectuées sur le terrain, sont intégrées au modèle de façon stochastique. Pour la génération des milieux fracturés numériques des algorithmes basés sur les méthodes statistiques et géostatistiques sont développés. Le comportement mécanique de modèles académiques et de structures réelles en maçonnerie est étudié grâce à la méthode Non Smooth Contact Dynamics (NSCD). Des structures en maçonneries telles que le monument historique de l amphithéâtre de Nîmes et l aqueduc d Arles sont étudiées, à échelle réelle, en deux et trois dimensions pour leurs comportements dynamiques pendant une sollicitation sismique. Les modèles de milieux rocheux fracturés engendrés à partir d études de cas sont analysés selon deux axes : l étude de la stabilité de pentes rocheuses et la conception de travaux souterrains par la méthode NSCD en utilisant le code LMGC90. La stabilité de ces modèles est étudiée en deux et trois dimensions. Les analyses effectuées sur ces modèles ont permis de proposer des recommandations pour l installation d éventuels soutènements. Elles ont également permis la distinction des familles des fractures jouant un rôle prépondérant dans l instabilité de ces massifs. La modélisation de certaines méthodes de protection en travaux au rocher telles que le boulonnage et les filets pare-pierres est ensuite abordée dans les perspectives envisagées comme développement de nos travauxThe numerical simulation is an essential tool for a better understanding of phenomena that occur within discrete environments, in particular in the fractured rock mass. This study aims to investigate the mechanical and dynamic behaviour of rock masses using discrete models in which surveyed data for orientation and inter-fracture spacing are introduced into the model in a stochastic way. For the generation of a jointed rock mass model, algorithms based on statistical and geostatistical methods are developed. The mechanical behaviour of academic models and real masonry structures is studied using the Not Smooth Contact Dynamics (NSCD) method. The dynamic behaviour, during seismic loading, of masonry structures such as the historic monuments of Nîmes amphitheatre and Arles aqueduct are studied, in real scale, in two and three dimensions. The models of fractured rock masses generated from case studies are analyzed with two objectives: the study of the stability of rock slopes and the design of underground structures by the NSCD method, using the LMGC90 code. The stability of these models is investigated in two and three dimensions. The tests performed on these models are used to make recommendations for the installation of support systems, where necessary. They also allow the distinction of the fracture sets playing a critical role in the instability of these masses. The modelling of protection systems, such as rock bolting and cable nets, is then addressed as a possible development of our workMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

The Non-Smooth Contact Dynamics method applied to the mechanical simulation of a jointed rock mass

A jointed rock mass geometrical model is built, based on the fracture systems characteristics obtained from field measurements. This model is composed of three-dimensional polyhedra interacting with each other by contact laws, in the frame work of the Non-Smooth Contact Dynamics method. The stability assessment of the walls of a stone quarry in France is presented, as a case study

Multi criteria analyses for managing motorway company facilities: the Decision Support System SINERGIE

International audienceImprovements to the decision-making process in the areas of preventive maintenance and facility repairs for a range of infrastructure entail maintenance, upgrading and retrofitting operations. Depending on the information available concerning the condition of facilities, specific types of projects can be programmed. Assigning priority action to a given project necessitates an evaluation process that introduces several criteria at various functional levels. This multi criteria (MC) evaluation is modelled as the aggregation of partial scores attributed to a project with regards to (w.r.t.) a given set of criteria. The scores are expressed over a finite scale which can cause some troubles when no attention is paid to the aggregation procedure. This paper deals with the consistency of the evaluation process, where scores are expressed as labels by experts (over finite discrete scales), whereas the aggregation model is supposed to deal with numerical values and cardinal scales. This is a curious but common apparent paradox in MC evaluation when engineering contexts are concerned. Adequate mathematical tools are provided to tackle related problems. A robustness analysis of the evaluation process concludes the mathematical part of the paper. The mathematical choices regarding our information processing chain meet the ESCOTA Motorway Company requirements. Indeed, ESCOTA aims at the formalization and improvement of the decisional process for preventive maintenance in a multi criteria (MC) framework. According to available pieces of knowledge on the infrastructure condition, projects are to be evaluated w.r.t. technical but also to conformity, security and financial criteria for planning purposes. ESCOTA's engineers used to manipulate symbolic labels but might convert them into more or less arbitrary numerical values when necessary without further care. The SINERGIE decision support system has been developed for ESCOTA to implement a logically sound information processing methodology. The SINERGIE man-machine interfaces are used to illustrate the way the mathematical concepts of the paper are used in terms of infrastructure management activities. The various information processing phases laid out in SINERGIE have been illustrated herein for road applications