Séminaire

Séminaire Le 10 mars 2020

Saint-Martin-d'Hères - Domaine universitaire

Introducing statistical mechanics framework into granular mechanics has been attempted both by physicists and mechanicians in recent decades. The talk overviews its recent outcomes and try to connects the two perspectives from physics and mechanics sides.

• En savoir plus sur Takashi Matsushima

Séminaire Le 22 janvier 2020

Saint-Martin-d'Hères - Domaine universitaire

Granular media and concrete are the ubiquitous natural and construction materials. X-ray tomography (XRT) has been used throughout the past three decades to qualitatively and quantitatively study the kinematics of deformation in these materials from meso- to microscales. However, quantifying the microscopic mechanisms of stress transmission and energy dissipation in these materials has traditionally been limited to 2D model materials or 3D numerical simulations. Such information can provide insight into the validity of microscopic contact laws, the statistics of forces and energy dissipation, and the pre- and post-failure load sharing within the materials’ microstructures.

In this talk, I will discuss experiments employing in-situ XRT and 3D X-ray diffraction (3DXRD) measurements during the deformation of 3D granular materials and cement. Using 3DXRD, each particle in the granular materials and cements acts as a stress gauge, providing both the local elastic stress tensors and the orientations of material points within the microstructure. I will highlight experiments with granular materials in which we quantitatively measured inter-particle forces, constitutive law parameters, per-particle fracture stresses, and energy dissipation mechanisms at each inter-particle contact. I will highlight an experiment on micro-concrete in which we quantified the stress distribution throughout the microstructure before and after fracture. I will discuss ongoing and future research directions in geomaterials with combined XRT and 3DXRD.

• En savoir plus sur Ryan Hurley

Séminaire Le 16 janvier 2020

Coupled Thermo-Hydro-Mechanical (THM) processes in particulate materials play an important role in a wide range of disciplines ranging from geomechanics to powder technologies. Despite an abundance of continuum based numerical approaches for simulating THM processes, the computational (and monetary) expense remains a prohibitive factor. During this presentation, a computationally efficient open-sourced discrete element based numerical method dedicated to the simulation of heat transfer and associated THM couplings in granular media is presented. Additionally, the numerical framework is validated analytically, numerically, and experimentally. The audience can expect to learn about the combination of heat transfer models comprising the conductive and advective heat transfer schemes as well as their mechanical couplings. In brief, the framework builds upon an existing pore finite volume (PFV) scheme to add conductive and advective heat transfer processes. Conductive heat transfer is modeled explicitly between and within solid and fluid phases: across DEM particle contacts, between adjacent tetrahedral pores, and between pores and incident particles. Meanwhile, advective heat transfer is added to the existing implicit fluid flow scheme by estimating mass energy flux from pressure induced fluid fluxes. In addition to the heat transfer model, a thermo-mechanical coupling is presented by considering pore space volume changes based on the thermal expansion of particles and fluid.

• En savoir plus sur Robert Caulk

Séminaire Le 17 septembre 2019

Our research on the influence of vegetation on soil mechanical and hydrological properties will be discussed at scales from the single root too the hill-slope.



Vegetation can reinforce soil slopes through both direct mechanical reinforcement and hydrological reinforcement, as plants generate suctions that increase effective stress between soil particles. We have studied relevant mechanical and hydrological processes at a range of scales: measuring the mechanical properties of individual plant roots; the reinforcement that roots offer to intact soil cores; the reinforcement of scaled model slopes within a geotechnical centrifuge subject to simulated rainfall events; and the monitoring of both mechanical and hydrological reinforcement of field-scale slopes. The effects of plant roots on changing soil structure and hydrology with time will also be considered. This talk will consider what we can learn from experiments and modelling at each scale, and where significant gaps still exist in our understanding. The potential to improve slope management by appropriate choice of species and management regime will be discussed, together with problems that may be caused when vegetation is removed and not replanted promptly.

 

 

• En savoir plus sur Glyn Bengough

Séminaire Le 21 novembre 2019

Diatomaceous soils, which are frequent in lacustrine or marine deposits, emerged as a singular type of materials showing unusual geotechnical properties characterized by high values of Atterberg limits, high natural water content, and high compressibility but complemented with high shear strength. The high liquid limit accompanied by high friction angles seems contradictory to the classical soil mechanics. However, several studies have shown that the unusual geotechnical properties of diatomaceous soils are related to the micromechanical features of the diatoms.



This investigation considers two diatoms species (Aulacoseira granulate and Centric Coscinodiscus) and identifies the effect of each type of diatom into the overall macroscopic behaviour of the soils. The study involves several tests of Atterberg limits as well as oedometric and triaxial tests on samples having different proportions of diatoms of the two different species. Results evidence that the shape of the diatom at the micro scale has observable trends in the macroscopic response of the soils.

Slides of the presentation (PDF, 9.64 Mo)

• En savoir plus sur Bernardo Caicedo

Séminaire Le 16 octobre 2019

Earthquake surface fault rupture can cause substantial structural damage and loss of life in near-fault regions. This hazard may be effectively modeled as a large-strain boundary-displacement problem governed by the fundamental granular nature of soil. Tremendous insights into the rupture mechanisms of granular soils are possible when soil is examined as a particulate medium with the characteristics of individual particles modeled numerically with the discrete element method (DEM). In this study, the interaction of a propagating fault rupture surface with a building foundation, called fault rupture-soil-foundation interaction (FR-SFI), is simulated in three dimensions using DEM with irregularly-shaped particles to capture the non-spherical nature of sand grains. High-performance computing simulations of free-field surface fault rupture and FR-SFI are validated against the results of geotechnical centrifuge experiments. Parametric analysis of the effects of soil density, modeled directly with particle assemblages having different void ratios, on FR-SFI is then performed with foundations of different contact pressures at different locations. Through quantitative analyses of inter-particle contact forces, particle rotations, particle displacements, and changes in void ratios, DEM provides insights on particle responses not possible with conventional continuum methods.

 

• En savoir plus sur Barbara Mazzolai

Séminaire Le 23 mai 2019

The thin floating sheet of ice covering the polar oceans is a complex material that breaks and drifts under the action of the winds and ocean currents. From a continuum mechanics point of view, it is both a damageable solid in which highly localized features emerge as a result of failure and a material that experiences high, permanent strains that dissipate stresses once fractured. In this sense, modelling its deformation lies between a solid mechanics and a fluid dynamics problem.

A new rheological framework was recently developed in the view of reproducing both the small deformations associated with fracturing processes within the sea ice cover and its large post-fracturing deformations in continuum global climate models or operational forecasting platforms. Inspired from previous models for the deformation of rocks and of the earth crust, it combines the concepts of elastic memory, progressive damage and viscous-like relaxation of stresses. It will be briefly described here, along with the statistical methods employed to validate the simulated mechanical behavior against the available satellite observations of sea ice deformation. Possible enhancements of this framework in a multi-scale modelling context will finally be discussed.

• En savoir plus sur Véronique Dansereau

Journée d'étude, Séminaire Du 3 juin 2019 au 4 juin 2019

Agglomération grenobloise

Comme chaque année, ces journées permettent à l'ensemble du laboratoire de se réunir à l'extérieur du campus pour partager des moments scientifiques, discuter de la vie du laboratoire, et mettre à profit des instants d'échanges plus informels voire ludiques pour mieux se connaître. En marge de ces sessions, nous avons pu également visiter la distillerie Meunier et assister à une conférence sur le chocolat. Un grand merci à l'équipe organisatrice !

Floriana Anselmucci, Maria-Celeste Blasone, Thanos Papazouglou, Mireille Pfister, François Villette jdl2019 [at] 3sr-grenoble.fr

• En savoir plus sur Journées du laboratoire

Séminaire Le 5 avril 2019

Saint-Martin-d'Hères - Domaine universitaire

Following H. Tomita and C. Murakami we propose an analytical model to predict critical probability of percolation. It is based on the excursion set theory which allows us to consider N-dimensional bounded regions. Details are given for the 3D case and statistically Representative Volume Elements are calculated. Finally generalisation to the N-dimensional case is made.



Download the slides here

Slides de la présentation (PDF, 5.39 Mo)

Emmanuel Roubin emmanuel.roubin [at] 3sr-grenoble.fr

• En savoir plus sur Emmanuel Roubin

Séminaire, Cérémonie Le 12 décembre 2018

Jacky Mazars et Félix Darve comptent parmi les plus importants contributeurs dans le domaine des sciences du génie civil et de la mécanique des solides. En l'honneur de leurs carrières (solides et non linéaires !), leurs collègues du laboratoire 3SR ont invité collègues et amis pour leur rendre hommage lors d'une conférence en deux sessions, l'une dédiée à la géomécanique, l'autre aux risques et à la vulnérabilité des ouvrages du génie civil. Tous deux devraient apprécier grandement ce bien beau cadeau jute avant Noël !

 

Programme du workshop (PDF, 690.35 Ko)

• En savoir plus sur Journée Risques et Vulnérabilité des structures de génie civil en l'honneur de Jacky Mazars