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Thèse de Donatien Rossat

le 4 octobre 2022
Bayesian techniques for inverse uncertainty quantification for multi-physics models of large containment structures

This work falls within the context of the aging of large concrete containment structures, such as reactor buildings in nuclear power plants. It aims at devising a numerical strategy for forecasting the long-term physical behavior of such structures, in order to better anticipate their maintenance.

Recent improvements of the understanding of physical phenomena behind aging and the increase of computational resources have enabled the development of numerical models aiming at simulating the Thermo-Hydro-Mechanical and Leakage (THML) behavior of large aging concrete structures. Nevertheless, the input parameters of such models are tainted with uncertainties, due to a lack of knowledge or to a natural randomness. Consequently, this thesis is mainly based on the general framework of Uncertainty Quantification (UQ), aiming at explicitly modeling uncertainties in numerical simulation. In this framework, the uncertainties tainting input parameters are typically modeled by probability laws, and are subsequently propagated through the model in order to study the variability of its response, or to estimate specific quantities of interest, such as moments or quantiles. However, THML computational models typically involve a large amount of uncertain parameters, most of them being not measurable directly. For this reason, the input probability law modeling their uncertainties is usually chosen in a subjective way, based on expert judgement. Then, this thesis is placed in the framework of Bayesian inference, in order to update a prior level of knowledge on input parameters from noisy observational data of the response of the structure under study.

Firstly, this work aims at coupling Bayesian inference with numerical techniques adapted with THML computational models, these last most often lying on costly finite element codes. In this perspective, a recent Bayesian computational framework is studied as an alternative to classical MCMC sampling techniques, and a coupling with surrogate modeling techniques is proposed in order to efficiently draw samples from posterior distributions with a reduced computational cost. Next, a general methodology aiming at performing probabilistic forecasts of the long-term THML behavior of containment structures is presented. In this context, the uncertainties of input parameters of the adopted THML model are quantified through Bayesian inference, from in-situ monitoring data. The proposed methodology is illustrated through a study of the VeRCoRs mock-up (1:3 scale nuclear containment building).


Lastly, in the framework of a reliability analysis, this thesis aims at estimating risks of exceeding regulatory leakage thresholds, while modeling the effect of eventual maintenance operations. In this framework, the impact of the choice of the inputs' probability law on some quantity of interest (including probabilities of failure) is assessed, through a robustness analysis. Next, a Bayesian approach aiming at updating both probabilities of failure and input parameters from monitoring data is presented. The overall methodology is applied to the realistic case of an operating 1:1 scale nuclear containment building.


Mme Clémentine PRIEUR (Université Grenoble Alpes/LJK, examinatrice)
Mr Franck SCHOEFS (Université de Nantes, rapporteur)
Mr Frédéric DUPRAT (INSA Toulouse, rapporteur)
Mr Pierre BEAUREPAIRE (SIGMA Clermont, examinateur);
Mr Julien BAROTH (Université Grenoble Alpes; Directeur de thèse)
Mr Frédéric DUFOUR (Grenoble INP; co-encadrant)
Mr Matthieu BRIFFAUT (Ecole Centrale Lille, co-encadrant)
MmeSylvie MICHEL-PONNELLE (EDF R&D, co-encadrante)
Mr Benoît MASSON (EDF/DIPNN/DT, co-encadrant)
Mr Alexandre MONTEIL (EDF/DIPNN/DR, co-encadrant)



Bâtiment GreEn-ER - 21 Avenue des Martyrs - 38031 GRENOBLE
Mis à jour le 14 septembre 2022

Thèse d'Alberto Terzolo

le 27 janvier 2022
Micro-mechanical modeling of human vocal folds : from quasi-static to vibratory loadings
Composed of collagen, elastin and muscular fibrous networks, human vocal folds are soft larygeal multilayered tissues owning remarkable vibro-mechanical performances. However, the impact of these tissues’ histological specifications on their overall mechanical properties remains elusive. Thereby, this work proposes a micro-mechanical model able to describe the 3D fibrous architecture and the surrounding matrices of the vocal-fold sublayers, and to predict their multiscale behavior accordingly. For each layer, the model parameters were identified using available histo-mechanical data, including their quasi-static response to physiological loading conditions (ie, tension, compression and shear). The evolution of microscopic descriptors such as fiber kinematics, deformation and interactions was simulated. Regardless of the loading mode, it was shown how macroscale nonlinear, viscoelastic and anisotropic tissue responses are inherited from fiber scale phenomena. Original scenarios of micro-mechanisms were also predicted for a large variety of loading conditions at various rates : (i) low-frequency cyclic and multiaxial loadings upon finite strains ; (ii) high-frequency small (SAOS) and large (LAOS) deformation oscillatory shear. In particular, the major role of 3D fiber orientation in tension, steric hindrance in compression, and the matrix contribution in shear was highlighted. Finally, the micromechanical model was implemented in a finite element (FE) code, yielding to a prior 3D simulation of vocal fold transient dynamics with relevant histo-mechanical properties. This work paves the way toward future multiscale simulations of vocal fold vibrations, accounting for various 3D fibrous healthy and pathological architectures.


Mme Aline BEL-BRUNON, Maître de Conférences, Institut National des Sciences Appliquées de Lyon (Examinatrice)
Mme Pascale ROYER, Directrice de Recherche, CNRS (Examinatrice)

M. Grégory CHAGNON, Professeur, Université Grenoble Alpes (Examinateur)
M. Stéphane LEJEUNES, Ingénieur de Recherche, CNRS (Rapporteur)
M. Yannick TILLIER, Professeur, École Nationale Supérieure des Mines de Paris (Rapporteur)
Mme Lucie BAILLY, Chargée de Recherche, CNRS (Directrice de thèse)
M. Laurent ORGÉAS, Directeur de Recherche, CNRS (Co-directeur de thèse)


  • Amphithéâtre André Rassat (Saint Martin d'Hères)
  • Zoom link for the audience
Mis à jour le 26 janvier 2022

Thèse de Alejandro Ortega Laborin

le 3 septembre 2021


An E-FEM generalisation for the modelling of triaxial fracture processes in composite quasi-brittle materials on the mesoscale
Representation of an element local fracture using the Embedded Finite Element Method approach (left and centre). The element is internally segmented in two different bodies possessing a set of fracture kinematic modes, where only translational and rotational are currently shown for the sake of clarity. In the right, the resulting local fracture networks in a concrete cubic sample simulation subject to a confinement pressure of 5 MPa and a progressive compressive load attaining a fully developed fracture process. Elements in a blue colour palette present a mode I local failure type while elements in a red colour palette exhibit a mode II failure mode with local sliding kinematics. Elements in purple have failed under compaction considerations.


Yann MALECOT Professeur des universités, Université Grenoble Alpes,Directeur de thèse
Jean-Baptiste COLLIAT Professeur des universités, Université de Lille, Rapporteur
Delphine BRANCHERIE  Maître de conférences, Université de Technologie Compiègne, Rapporteure
Nicolas MOËS Professeur des universités, École Centrale de Nantes, Examinateur
Bert SLUYS Professeur des universités, Delft University of Technology, Examinateur
Loredana CONTRAFATTO Professeur associé, Catania University, Examinatrice
Gioacchino VIGGIANI Professeur des universités, Université Grenoble Alpes, Examinateur
Codirection :
Professeur des universités, Université Grenoble Alpes, Codirecteur de thèse
Emmanuel ROUBIN
Maître de conférences, Université Grenoble Alpes, Co-encadrant de thèse


Mis à jour le 23 août 2021
Problematic and methodology of the PhD
Problematic and methodology of the PhD

Thèse de Marielle Dargaud

le 23 avril 2021

Suivre en direct ici

Experimental and numerical analysis of the failure modes induced in ceramic materials under dynamic loading

Due to their high resistance to extreme loading conditions, ceramic materials have been extensively investigated to be part of vehicle and body armour protections. Combined to a ductile backing, ceramics are very interesting for lightweight bulletproof systems. The link between damage mechanisms occurring in the ceramic upon impact and its microstructural properties is still not well understood. For this reason, a make-and-shot iterative approach is the common way followed to develop this type of material. However, such an optimisation process is very expensive, time consuming and hardly leads to any conclusions on the link between microstructural features and ballistic performance. The first goal of this PhD is to bring insight on the connection between microstructural properties of the ceramic armour and its failure mechanisms under dynamic loading. The natural second step consists in using these results to improve a modelling, which is representative of ceramic brittle damage under tensile loading on a large range of strain rates.

Ceramics are highly sensitive to the presence of inherent defects. Under low loading rate, they have a stochastic strength linked to the size of the most critical defect in the loaded volume. The common approach consists in using quasi-static tests to identify the defects responsible for failure (Weibull approach) and assumes that the same ones are causing failure at high loading rates. Such an assumption is questioned in the present work. Under high strain rate, numerous cracks are triggered simultaneously from multiple defects, causing an intense and deterministic fragmentation. Six ceramic materials, presenting different microstructural features, are analysed and tested under dynamic conditions in this project. Highly instrumented edge-on impact, normal impact and tandem impact dynamic tests, combined with a micro-tomography analysis of damage patterns, provided a better understanding of the fragmentation properties of the different grades of ceramics. A shockless experimental spalling technique was developed to evaluate the intrinsic tensile strength sensitivity to strain-rate of ceramic materials. To do so, the plate-impact configuration was adapted, using specific flyer-plate geometries designed to generate a tailored loading in the sample. From a hybrid approach mixing numerical simulations and experimental results, the spall-strength of the tested ceramic can be related to a well-controlled loading rate.

A new methodology is proposed to model the multiple fragmentation process induced in ceramics under high strain rate. This method is built on the identification of material defects (mainly pores) from micro-tomography analysis. This realistic description of the defect distribution is explicitly implemented in the Denoual-Forquin-Hild (DFH) damage model to predict the dynamic failure behaviour of ceramics under tensile loading, through so-called continuous and discrete approaches. A comparison with experimental results of fragmentation and spalling tests provided a validation of the approach. Predictions of this micro-mechanical model were compared for a Weibullian distribution of critical defects and a description based on micro-tomography analyses. Comparisons on a large range of strain rates showed that, for materials presenting multiple flaw populations, the Weibull-based solution is highly invalid. In this case, the use of a proper flaw description, obtained via micro-tomography, is much more relevant. These results highlight the importance of considering microstructural features to properly model the failure behaviour of ceramics at high loading rate, and therefore move toward a design of the next generation of ceramic-based armour protections.

Mr. Alexandre MAÎTRE Professor, University of Limoges – President
Mr. Yannick CHAMPION Research director CNRS, Laboratoire SIMaP – Vice-President
Mr. Stéphane ROUX Research director CNRS, ENS Paris Saclay – Reviewer
Mr. Michel ARRIGONI University Professor, ENSTA Bretagne – Reviewer
Mr. Daniel EAKINS Associate Professor, University of Oxford – Examiner
Mr. Eric BUZAUD PhD Engineer, CEA Gramat – Examiner
Mr. Emmanuel BONNET Ingénieur, R&D LafargeHolcim, Invited
Mr.  Pascal FORQUIN University Professor, Laboratoire 3SR – PhD Director, Examiner

Mr. Jérôme BRULIN PhD Engineer, Saint-Gobain Research Provence – Co-supervisor, Invited
Ms. Alexane MARGOSSIAN PhD Engineer, Saint-Gobain Research Provence – Co-supervisor, Invited
François BARTHELEMY PhD Engineer, DGA Techniques Terrestres – Co-supervisor, Invited


amphitheatre Kilian 1381 Rue de la Piscine, 38610 Gières
Mis à jour le 16 avril 2021
Flowchart of experimental and numerical works
Flowchart of experimental and numerical works

Thèse de Maria Blasone

le 24 mars 2021
Experimental testing and numerical modelling of the tensile and compression damage in Ultra-High Performance Concrete under impact loading
This thesis presents experimental and numerical investigations on Ultra-High Performance Concretes (UHPC) in view of intensifying their use in application demanding resistance to impact loadings. Under impact, concrete is exposed to high confinement stresses and high tensile loading rates, leading to severe damage modes affecting the ballistic performance. The DFHcoh-KST coupled model, describing the behavior under both confinement and dynamic tension, has been chosen to simulate with a Finite Element (FE) code the response of UHPC targets with fibre reinforcement under impact. In the model, the confining pressure is influencing the volumetric strain and the deviatoric strength. The strain rate effects are included in the description of the tensile damage based on the activation and obscuration of a Weibull distribution of flaws. The role of the fibres is integrated introducing a cohesion strength term.
The material parameters were identified for two Ductal® formulations using existing experimental techniques (Quasi-Oedometric Compression (Q-OC) tests, bending tests, and spalling tests at the Hopkinson bar) covering confinement pressure up to 500 MPa and a range of strain rates from 10-5 to 102 s−1. The validity domain of the proposed model was extended at very-high strain rates (above 103 s−1) by performing additional plate-impact tests, investigating the tensile response. A new testing technique employing a pulse shaping system to ensure a constant loading rate in the specimen was designed using numerical simulation and experienced using the single-stage gas gun installed in the 3SR laboratory.  The fragmentation under dynamic tension was simulated with discrete and continuous  micro-mechanics approaches based on X-ray Computed Tomography (CT) observations of the UHPC microstructure expressed as distribution of porosity. Assuming that the size of a pore is related to its stress of activation and that pores are connected to wing-end cracks about the size of the largest aggregate in the concrete formulation led to a flaw population that correctly described the observed tensile strength in the range of 103 - 104 s-1.

Mr. Pascal FORQUIN Professor, Université Grenoble Alpes, Directeur de thèse
Mr. Marco DIPRISCO Professor, Politecnico di Milano, Reviewer
Mr. Jaap WEERHEIJM Associate Professor, TU Delft, Reviewer
Mr. François TOUTLEMONDE Ingénieur Général des Ponts, Université Gustave Eiffel, Examiner
Ms. Magali ARLERY Ingénieur, CEA/DAM, Examiner
Mr. Jean-Luc HANUS Associate Professor, INSA Centre Val de Loire, Examiner
Mr. Emmanuel BONNET Ingénieur, R&D LafargeHolcim, Invited
Mr. Dominique SALETTI Associate Professor, Université Grenoble Alpes,  Invited
Mr. Julien BAROTH Associate Professor, Université Grenoble Alpes, Invited


Grenoble - Presqu'île
amphi P05 bâtiment Polygone (GreEn ER) 21 Avenue des Martyrs  38000 Grenoble
Mis à jour le 22 mars 2021
Slices of the 3D reconstructions of the neutron and x-ray tomographies of the concrete sample*
Slices of the 3D reconstructions of the neutron and x-ray tomographies of the concrete sample*

Thèse de Hani Cheikh Sleiman

le 28 janvier 2021
Contribution of neutron /X-ray tomography for the drying modelling of cohesive porous media

The drying of cement-based materials affects directly their durability, which has a major economic, societal, and environmental impact.
The conventional experimental techniques such as gravimetric and sensor-based measurements, which are employed to study the drying-driven processes, provide only bulk-averaged or point-wise measurements which are not sufficient to characterize these processes. However, the significant advances in full-field techniques have allowed unprecedented insight into these local processes. Notably, for cement-based materials, x-ray and neutron tomography lend themselves as highly complementary tools for the study of their THM behavior. In fact, the high sensitivity to density variations of x-ray imaging gives access to the developments of fractures, in 4D (3D+time). On the other hand, neutron tomography allows the study of the evolution of the moisture field in 4D, thanks to its high hydrogen sensitivity.
This Ph.D. takes advantage of these two highly complementary techniques, which, together with advanced numerical modelling tools, allowed for a novel experimental/numerical insight to study the drying-driven physical processes in cement-based materials. In this work, two experimental campaigns were performed at the NeXT instrument located at the ILL. In the first campaign, neutron tomography was employed to characterize the moisture distribution of a set of cylindrical mortar samples which were set to dry sequentially in a TH controlled environment (T=20 ºC, RH=35 %) to represent different hydric states. The main phases of the mortar (aggregates, cement paste, and voids were separated, and saturation profiles were deduced and validated against the weight loss measurements. In the second experimental campaign, more complexity was added to the experimental drying conditions by heating concrete and cement paste samples up to moderate temperature which has led to the appearance of cracks in the later sample. The analysis of the acquired simultaneous neutron/x-ray data-set (once aligned in time and across modalities) allowed for the quantification of the 4D moisture profiles which were found to predict an overall water loss at hydric equilibrium coherent with the corresponding analytical analysis. In the cement paste sample, the x-ray dataset captures the evolution of an extensive cracking network, opening, and propagation toward the core of the sample. Then, a novel analysis procedure was proposed which allowed the extraction of these fractures and the analysis of their interplay with local drying as captured through neutron imaging.
On the other hand, the numerical approach employed in this study consisted of improving the numerical model predictive capacity by assessing the implications of common simplifications on the modelling response. These common simplifications can be divided in three main categories which regard the consideration of gaseous transport modes, the TH and HM couplings, and the morphological description of the material. Quantification of these simplifications effects regarding the used model and the choice of TH coupling laws was done by comparing mass loss response surfaces in relative humidity and temperature space for multiple configurations. The results show relative error maps at early, mid, and late drying stages for every compared case. On the other hand, the simplification regarding the HM coupling was evaluated in a 2D mesoscopic simulation framework where an artificial concrete mesostructure had to be generated for cracking localization purposes. The cracking impact was then assessed both locally on the saturation fields and on the global mass loss response. Finally, a CT-FE mapping scheme was proposed which consisted of extracting the mesoscale morphology of concrete (aggregates and pores) from x-ray/neutron attenuation fields and presenting it explicitly on a FE mesh. This has permitted to perform 3D multiphase THM simulation of concrete at the mesoscale.


M. Farid BENBOUDJEMA, Professeur à l’École Normale Supérieure Paris-Saclay, Rapporteur
Mme. Catherine DAVY, Professeur à l’École Centrale de Lille, Rapporteur
M. Fekri MEFTAH, Professeur à l’INSA Rennes, Examinateur
M. Giuseppe SCIUME, Maître de conférences à l’Université de Bordeaux, Examinateur
M. Bruno HUET, Docteur Ingénieur de recherche chez LafargeHolcim R&D, Examinateur
M. Jean-Luc ADIA, Docteur Ingénieur de recherche chez EDF R&D, Invité
M. Matthieu BRIFFAUT, Maître de conférences HDR à l’université Grenoble Alpes, Directeur de thèse
M. Stefano DAL PONT, Professeur à l’université Grenoble Alpes, Co-encadrant
M. Alessandro TENGATTINI, Maître de conférences à l’université Grenoble Alpes, Co-encadrant

Vertical and horizontal slices of the 3D reconstructions of the neutron and x-ray tomographies of the concrete sample, highlighting the high complementary of the micro-structural information obtained with these techniques. The neutron attenuation field (the average attenuation of the materials contained in a voxel μn) on the left of the partially saturated concrete sample highlights aggregates and pores from the cement paste which is further differentiated in dry and wet. Nonetheless pores and aggregates have comparable attenuation in the neutron tomography whereas they have significantly different x-ray attenuations μx, as shown on the right.


Remote session
Mis à jour le 15 décembre 2020
Some major results from the PhD*
Some major results from the PhD*

Thèse de Yannick Duplan

le 14 décembre 2020
Experimental characterisation and modelling of the dynamic fracture and fragmentation properties of a projectile ammunition and armour ceramics

Some ceramic grades, such as silicon carbide (SiC) or alumina (Al2O3), are used as ballistic materials thanks to their excellent mechanical performances, such as their hardness, while being light, where weight gain is a major issue for the design of military equipment for personal and vehicle protection. Since the Vietnam War, ceramics have been largely used and integrated as front face in bilayer shielding to stop the threat of AP (Armour Piercing)-type projectiles during a ballistic impact. Nevertheless, the projectile leads to an intense damage in the ceramic due to, amongst other phenomena, a dynamic tensile loading that manifests by multiple cracking, called fragmentation, particularly unfavourable for the integrity of the ballistic protection and its capacity to deal with a second impact. In order to develop a more performing shielding material, it is essential to understand the link between the microstructure of ceramics, the damage generated under impact and their ballistic performances.

This thesis seeks to better understand the dynamic fragmentation phenomenon generated at high strain rates in high fracture-toughness ceramics, including a bio-inspired alumina material mimicking nacre microstructure. This artificial nacre is, a priori, more crack resistant than conventional ceramics as it is characterised by a high static fracture-toughness due to its specific “Brick-and-Mortar” (or BM) microstructure reproduced in the material called here MAINa.


Daniel RITTEL, Professor, Technion - Israel Institute of Technology, Reviewer
Thibaut de RESSÉGUIER, Research director, Université de Poitiers, Reviewer
Frédéric BERNARD, Professor, Université de Bourgogne, Examiner
Jean-Luc ZINSZNER, Researcher, CEA/DAM Gramat, Examiner
François BARTHÉLEMY, Engineer, DGA Techniques Terrestres, Examiner
Pascal FORQUIN, Professor, Université Grenoble Alpes, Examiner
Alexane MARGOSSIAN, R&D engineer, Saint-Gobain Research Provence, Invited
Dominique SALETTI, Assistant Professor, Université Grenoble Alpes, Invited

* Image caption

Some major results from the PhD: steel core extracted from API-BZ bullet with MAINa microstructure observed in Scanning Electron Microscopy (chapter 2); comparison between the experimental force-displacement response along with the numerical response using the identified experimental law of the steel core (chapter 3); numerical simulation of the penetration process of the steel core (800 m/s) in a SiC ceramic, 56 μs after impact (chapter 4); dynamic cracking of MAINa microstructure, tested in two orientations of platelets during Rockspall tests (chapter 5); multiple fragmentation of MAINa samples (0° orientation) after both Edge-On-Impact test in sarcophagus configuration and tandem test with tomographic segmentation (chapter 6).


Saint-Martin-d'Hères - Domaine universitaire

Kilian auditorium - ISTerre - 1381 Rue de la Piscine / 38610 / Gières

Mis à jour le 2 décembre 2020
Monopile in calibration chamber
Monopile in calibration chamber

Thèse de Ritesh Gupta

le 15 mai 2020
Behavior of monopile under combined cyclic load
Monopile is the most common foundation system for offshore wind turbine structures, statistically about 73%, as per Wind Europe, 2020 report. A pile can be defined as flexible or rigid depending on the embedded length to diameter ratio (Le/D) and the relative stiffness of pile and soil. The existing codes for pile design are mainly developed for flexible piles, whereas monopile for new offshore wind turbines typically falls in the rigid category. The dominant complex cyclic wind and waves loads on offshore wind turbine structure and consequently on the monopile foundation, act in the lateral direction. The API design procedure, representing the lateral and vertical soil response through uncoupled non-linear springs, is developed for flexible piles and is recognised as conservative for rigid piles. The behaviour shall represent a coupled vertical and lateral soil-structure interaction because a rigid pile presents rotation deformation mode instead of deflection. The deformation mode further demands a different formulation mechanism, including the distributed moments along the pile shaft and shear & moment behaviours at the pile base as an essential part of the soil response investigations.
This work presents the numerical models aimed to address the limited understanding of coupling consideration of monopile installed in sand. The cone penetration tests performed in the calibration chamber, data treatment with ICP method and available Fontainebleau sand NE34 properties database in the literature provide the constituent parameters for model definition.
First, a PLAXIS 3D finite element model presents the model pile in the calibration chamber configuration with representative boundary conditions and the constitutive behaviour of the sand. The model pile geometry and load magnitudes are the outcomes of a similitude relationship with a representative prototype. A constant mass placed on the pile head represents the vertical load (the dead weight of the wind turbine structure). A simplified lateral point load represents the complex environmental loads, acting at a distance above foundation level, represents the lateral and moment load at mudline. Thus, vertical (V), lateral (H) and moment (M) collectively represent the combined load, investigated in both monotonic and cyclic loading cases. Different combined loading cases in the limits of horizontal and vertical load capacities represent the overall behaviour of the model pile. The observation of normal and shear stress changes close to the pile-soil interface at different depths quantify the pile-soil interaction. The response investigation at some strategic stress points in the FE model soil volume provides a basis for soil-stress transducers (SSTs) layout plan in the experimental soil volume. A methodology to formulate the lateral and shear stresses evolution close to the pile surface as representative of the coupled interaction is presented.
Second, a local-macro element (LME) model, an assembly of non-linear springs formulated using a Matlab toolbox ATL4S, presents the soil-pile interaction with inherent coupling considerations at different embedment depths. The PLAXIS model outcomes define the basis for a corresponding model scale LME model. The obtained results from both numerical investigations demonstrate the significance of vertical-lateral coupled interaction as a set of hypothesised equations for rigid monopile foundation. A similitude work provides a relation between a prototype scale and the lab-scale monopile model. It further aids in comparison and validation with the available experimental and numerical results in the literature.




Galilée room 108
Mis à jour le 30 novembre 2020
Image process to detect each phase within the system and extract the 3D root system and follow its time and space evolution.
Image process to detect each phase within the system and extract the 3D root system and follow its time and space evolution.

Thèse de Anselmucci Floriana

le 17 novembre 2020
Root-soil interaction: effects on soil microstructure
This PhD thesis presents an innovative experimental investigation on the mechanical response of sand to plant root growth. Root-soil interaction is investigated for two different root systems -- Maize and Chickpea -- and two different gradings of Hostun sand with two initial porosities.

An original protocol is developed aiming to create samples with repetitive initial nominal properties and representative of the natural interaction. Two experimental campaigns were run on a series of samples with different sands and plants. A 4D (3D+time) analysis of the interaction is carried out by using x-ray Computed Tomography. For each sample, an average of 7 x-rays scans is performed, from the day of the seed sowing up to 7-days-old root system. An image processing technique has been developed and it is applied to the 3D images resulting from the reconstrution of the x-ray scans. Through this image processing, the root system is identified, together with the sand grains and the water present in the system. Finally, a four-phased volume representative of the soil-root system can be defined for each state of the observed samples. Besides, from the 3D greyscale images of the samples, measurements of the kinematics of the system are obtained through local and discrete approaches of image correlation. Local sand porosity and deformations resulting from the four-phased volumes and the image correlations are detailed for one sample of each root-sand configuration.

Regarding the impact of the initial sand state on the root system development, the comparison of the different configurations shows, among other things, that the sand density plays a key role on the expansion of the root system, for both plant species. Concerning the sand response to the root growth, the strain tensor computed with image correlation shows that a root shears the soil while growing and the sheared zone is wider when the initial bulk density is lower.

This work focuses also on the determination of the sand volumetric response to root growth in the sheared zone and its dependency on the soil density. Sand response is purely dilatant for denser initial states, while the looser sand exhibits a contractant behaviour far from the root surface. Such a response is obtained in the case of both maize and chickpea. Moreover, the contractant behaviour induced by the shearing away from the root is con_rmed also for both sand granulometries in a looser state.


Monsieur Laurent OXARANGO - Professor, Universitè Grenoble Alpes, President
Monsieur Jean-Yves DELENNE - Research director, Inrae centre occitanie - Montpellier, Reviewer
Monsieur Alessandro TARANTINO - Professor, University of Strathclyde (UK), Reviewer
Monsieur Edward ANDÒ - Research Engineer, CNRS, Examiner
Monsieur Glyn BENGOUGH - Professor, University of Dundee (UK), Examiner
Madame Barbara MAZZOLAI - Research director, Italian Institute of Technology (Italy), Examiner
Monsieur Gioacchino VIGGIANI - Professor, Universitè Grenoble Alpes, Invited
Monsieur Luc SIBILLE - Maitre de conference, Universitè Grenoble Alpes, Thesis Advisor
Madame Chloé ARSON - Associate Professor, Georgia Institute of Technology (USA), Thesis Co-advisor


Galilée room 003
Mis à jour le 27 novembre 2020
Comparison between experimental and numerical crack patterns under uniaxial tension
Comparison between experimental and numerical crack patterns under uniaxial tension

Thèse de Olga Stamati

le 24 janvier 2020
à 10h30
Impact of meso-scale heterogeneities on the mechanical behaviour of concrete: insights from in-situ x-ray tomography and E-FEM modelling
This doctoral thesis investigates the impact of the meso-scale heterogeneities of concrete (aggregates and macro-pores) on its macroscopic mechanical response. A combined numerical and experimental approach is adopted to study the progressive evolution of the 3D fracturing processes of micro-concrete specimens under uniaxial tension, uniaxial compression and triaxial compression.

Part of the originality of this work lies in the exploration of multiple loading paths on concrete samples of realistic composition (including cement, sand, aggregates and water) and in the in-situ nature of the experiments conducted. The experimental campaign is performed inside an x-ray scanner, which allows the internal structure of the material to be non-destructively captured and its evolution from the intact (before loading) until the damaged (after unloading) state to be followed and quantified. The 3D images coming from the x-ray scans are first analysed in order to quantitatively describe the morphology of the meso-structure (aggregates, mortar matrix and macro-pores). A timeseries analysis of the set of 3D images coming from each in-situ test follows, which allows for the measurement of the 3D kinematic fields (displacement and strain fields) throughout the experiments.

On the numerical side, the identified morphologies coming from the intact x-rays scans are given as an input to a FE meso-model with enhanced discontinuities. The originality of the numerical simulations comes from their 3D nature and the consideration of the actual meso-structure of the micro-concrete specimens, based on the segmentation of the three phases of the material. After a calibration of the model in uniaxial tension, its predictive ability is challenged under different stress paths in compression. An extensive comparison is presented between experimental and numerical observations, in terms of macroscopic responses, displacement fields, fracturing processes and failure patterns. The typical asymmetric behaviour of concrete in tension and compression, as well as the increase of strength and ductility with the increase of confinement are sufficiently captured numerically. Starting from an x-ray scan, it is shown that the model is able to satisfactorily Sreproduce some of the basic characteristic features of the failure modes observed experimentally for the different loading paths studied.
While validating the numerical results and through a combination of numerical and experimental observations, the significant impact of the meso-scale heterogeneities on the local failure mechanisms is revealed. It is shown that, for the studied material, the shape and location of the largest aggregates and macro-pores are essentially driving the fracture patterns under simple tension, simple compression and triaxial compression. The good correspondence between experiments and model strongly suggests that the explicit representation of these heterogeneities is the key feature that allows the predictive power of the model. A further insight into the impact of the meso-structure is obtained by investigating virtual concrete morphologies, generated by modifying the real meso-structures coming from the x-ray scans.


François HILD, Directeur de Recherche CNRS, ENS Paris-Saclay, Rapporteur
Julien YVONNET, Professeur, Université Paris-Est Marne-la-Vallée, Rapporteur
Camille CHATEAU, Chargée de Recherche, École des Ponts ParisTech, Examinatrice
Jean-Baptiste COLLIAT, Professeur, Université de Lille, Examinateur
Ryan HURLEY, Assistant Professor, Johns Hopkins University, Examinateur
Yann MALECOT, Professeur, Université Grenoble Alpes, Directeur de thèse
Edward ANDÒ, Ingénieur de Recherche, CNRS, Co-encadrant de thèse
Emmanuel ROUBIN, MCF, Université Grenoble Alpes, Co-encadrant de thèse


Saint-Martin-d'Hères - Domaine universitaire
Amphi Wilfrid Kilian - OSUG/ISTerre
Mis à jour le 14 janvier 2020