Experimental and Numerical Study of Cracking During the Desiccation of Porous Materials : Application to the Fields of Chemical Engineering and Geomechanics

• Main Author: Hubert, Julien
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2018
• Subjects: Boundary conditions; Chemical engineering; Crack initiation; Hydrogels; Materials science; Mathematics; Mechanics; Porous materials; Tensile strength; Tension tests
• ISBN: 9798384159186

Porous material drying is a process used in many engineering fields such as food (conversation), plastic (polymer), chemical, pharmaceutical and wood (paper paste, composite beam for construction) industries as well as any manufactured process based on paste or powder. It is also of importance in civil engineering because of its impact on soil properties and soil-structure interaction. Given, the number and the importance of these applications, it is a thoroughly studied phenomenon and this PhD work aims at furthering our understanding of the mechanisms behind it as well as those controlling desiccation cracking.This PhD work is part of a F.R.S-FNRS project revolving around unsaturated porous material desiccation cracking and supported by the collaboration of research groups from the geomechanical team (GEO3) and the chemical engineering team (LGC) of the University of Liège which is the principal strength of this work : it combines the experimental expertise of the LGC team with the numerical knowledge of the GEO3 team. This allow to collect a vast amount of data which are used to validate the numerical models. Sensitivity studies are also conducted to get a better understanding of the influence of each individual process.ShrinkageFor the geomechanical research group of the University of Liège, the study of the drying behavior is conducted under the scope of deep geological storage of nuclear wastes. This follows previous works of the team carried on nuclear wastes disposal. This concept is based on the multi-barrier principle : wastes isolation is guaranteed by the combination of natural and engineered barriers. During the operation phase, these tunnels are ventilated to allow for people circulation which may lead to desiccation of the host rock at the surface of the tunnel and to cracking.Given the importance of ensuring good sealing conditions, understanding the drying behavior of the host rock is essential. In Belgium, the considered potential host rock is Boom clay which is thus the material studied throughout the first part of this PhD work. On a geological timescale, this formation belongs to the Rupelian (from 36 to 30 million years ago). This formation is located in the Mol area in the north of Belgium. It is constituted of an alternation of silty clay layer and more clayey layer. This clay structure leads to a material presenting a strong orthotropy. Boom clay has been chosen as a potential host rock because of a series of properties making it a suitable candidate :• Very low hydraulic conductivity ;• Good radionucleide retention capacity ;• Has been stable for millions of years ;• Self healing capacity.An experimental convective drying campaign is conducted to gather the data required for the validation of our numerical model. This campaign used the infrastructure of the LGC team of the University of Liège. More specifically, the use of an X-ray microtomograph and the expertise of the LGC in terms of image analysis has been instrumental in quantifying very accurately the variation of volume of the samples. Based on those data, thermo-hydro-mechanical simulations have been performed using the finite element code LAGAMINE (developed by the GEO3 team) to reproduce the experimental observations. A comprehensive step by step approach is followed highlighting the influence of each mechanism on the overall process. Overall, the simulations lead to a excellent fit of the experimental results.