(Microengineering and medical devices) Theoretical and experimental study of capillary forces in granular media | BEAMS

(Microengineering and medical devices) Theoretical and experimental study of capillary forces in granular media

Project information
Project type: 
Master thesis
Academic year: 
2012-2013
Status: 
Defended
Research unit: 
Micro-Bio-Mechatronics
BEAMS supervisors
Manager
External supervisors
Bertrand François
Manager
Student(s)
Roos Evenepoel

Contexte / Context The effective stress principle and its formulation in unsaturated porous media is a key to understand the behavior of unsaturated porous material, in general and unsaturated soils in particular. For saturated material, Karl Terzaghi (1920) demonstrated experimentally the concept of effective stress which is the fundaments of classical soil mechanics. Under unsaturated conditions (when a part of the void space is occupied by air), the state of stress is fundamentally different. The relative amounts and corresponding pressures of the pore water and pore air phases in unsaturated soil have a direct impact on the state of stress acting at the particle-particle contacts and, consequently, on the macroscopic physical behavior of the soil mass. In that framework, the concept of effective stress and its extension from saturated to unsaturated porous media has been the subject of much research, but there is no consensus yet in this regard. Various approaches have been used to get insights into this concept. Geometrical representation of liquid bridge between two spherical particles (from Soulié et al., 2006) Objectifs du travail / Project goals The objective of this work is to investigate, from micro-mechanical experiments, the possibility of obtaining an effective stress deduced from the measurement of capillary forces between spherical particles. - First, the effective stress can be defined as the sum of the contact forces between particles divided by the total area. Micro-mechanical experiments that measure capillary forces between two or several spherical particles linked by water meniscus will be conducted to deduce effective stress. - Secondly, normal effective stress can also be defined as the normal stress for which the Mohr-Coulomb failure criterion is independent on the amount of water stored in the meniscus. So, a second series of micro-mechanical tests will be conducted in order to measure the shear strength between two or several spherical particles linked by water meniscus. - Finally, from a macroscopic point of view, effective stress can be defined as a stress for which the Mohr-Coulomb failure criterion is not affected by the amount of water stored in the material. Macroscopic direct shear tests will be performed at various water contents to deduce a macroscopic effective stress for unsaturated granular material, expressed as a function of the water content. Those experimental tests will be carried out together with a theoretical formulation (analytical or numerical) of the encountered capillary forces between spheres. Références / References Soulié F, Cherblanc F, El Youssoufi MS, Saix C. Influence of liquid bridges on the mechanical behaviour of polydisperse granular materials. International Journal for Numerical and Analytical Methods in Geomechanics 2006; 30:213–228. Lambert P, Chau A, Delchambre A, Régnier S. Comparison between two capillary forces models. Langmuir 2008; 24(7):3157–3163. Gabrielli F, Lambert P, Cola S, Calvetti F. Micromechanical modelling of erosion due to evaporation in a partially wet granular slope. International Journal for Numerical and Analytical Methods in Geomechanics 2012, DOI: 10.1002/nag.1038. Profil recherché / Targeted skills Etudiants de la filière EM, CC, Physique, compétences expérimentales et/ou numériques (Matlab) Bruface students in electromechanics, civil engineering, physics with experimental or numerical skills (Matlab) Langue de travail / Working Language Français / English Encadrement / Supervision Prof. Pierre LAMBERT (BEAMS), Prof. Bertrand FRANCOIS (BAtir), Mohamed Oualmakran Contact(s) pierre [dot] lambert [at] ulb [dot] ac [dot] be, Bertrand [dot] francois [at] ulb [dot] ac [dot] be

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