Plate boundary fault zones exhibit a wide range of dynamic behaviors, from aseismic slip to mega-earthquakes. So far, there is no consensus on a model describing the processes controlling these fault behaviors. A possible answer might lie in the properties of smectite, a swelling clay mineral that form the core of many of the fault zones and that is able to adsorb significant amounts of water in-between nanometric minerals. Despite their potential importance, the thermodynamics of hydration/dehydration reactions in smectite and the connections between these reactions and the fault deformations, is not yet known. These fundamental questions are the heart of the ANR project SMEC funding this Ph.D. position. This Ph.D. project focuses on the modeling of part of the SMEC project. More precisely, we propose to combine molecular simulations, granular modeling and micromechanics in order to relate the hydration/dehydration reactions of smectites to the mechanical behavior of faults zones.

Inflatable structures have many applications in multiple fields such as architecture, entertainment, robotics and more. They can be used for temporary shelters, soft robots, floating devices (pneumatic canoes), furniture (inflatable mattresses), safety equipment (air bags) or medical equipment (cushions, prosthetics). This wide range of applications is motivated by the numerous advantages of this type of structure which are at the same time light, inexpensive, safe and resistant.

Bio-based construction materials are systems containing or formed of vegetal particles, such as wood, hemp, cellulose, flax, cotton, etc., possibly linked with a mineral paste or an organic binder. They represent a promising solution for carbon emission reduction, due to their low production cost and their partial or full recyclability. Moreover, they bring more comfort to the occupants thanks to their moisture-buffering capacity, and they require less energy for heating or cooling. These qualities are obtained through exchanges between water vapor and “bound water”, i.e., water absorbed in the solid structure, combined with heat transfers. Consequently, understanding and predicting water and heat (hygrothermal) transfers in such materials is essential to selecting them appropriately, adjusting their conditions of use, and designing innovative materials. However, the current analysis of their performance is generally based on limited evaluations at a global scale or via macroscopic models lacking physical information.

In hydrocarbons producing fields, Produced Water Re-Injection (PWRI) is known as an economically attractive and environmentally friendly method to manage the produced water. This method has the advantage to maintain the pressure level in the reservoir in order to enhance the hydrocarbon production. However, this technique faces challenges such as the deterioration of the injectivity due to the filtration, around the injection well, of suspended solid particles contained in the produced water. Re-injection in the so-called ‘fracturing regime’ is an option to maintain the injectivity by fracturing the clogged zone formed by the agglomeration of fine particles at the face of the injected formation. However, controlling the injection in the fracturing regime is a key issue for the safety of the production as fracturing should not deteriorate the cap rock integrity. Hydraulic fracturing has been extensively studied for brittle rocks with low permeability and is dominated by tensile failure. However, the mechanisms involved in fracturing of unconsolidated reservoirs which behave as cohesionless granular materials are fundamentally different and are controlled by shear failure, fluidization and induced channelization around the injection point.

Water transfers in bio-based materials such as wood, plants, paper, hair, natural textiles are essential in our everyday life, but their physics is still poorly known. A specificity of these materials is that they are hygroscopic, i.e., they can absorb, from vapor, a huge amount of water in the form of nanoscale water inclusions between the microfibrils of cellulosic or keratin fibers. This so-called “bound water”, which evaporates in a dry ambient air, is at the origin of the swelling or shrinkage of these materials. Moreover this bound water appears to be very mobile, i.e., it can diffuse throughout the material. The bound water diffusion and its exchanges with free (capillary) water and vapor, are key to the physics of water transfers in such materials, which in turn is key to reducing energy consumption for ventilation and heating, or controlling various processes such as the wetting or drying of such materials.

Plate boundary fault zones exhibit a wide range of dynamic behaviors, from aseismic slip to mega-earthquakes. So far, there is no consensus on a model describing the processes controlling these fault behaviors. A possible answer might lie in the properties of smectite, a swelling clay mineral that form the core of many of the fault zones and that is able to adsorb significant amounts of water in-between nanometric minerals. Despite their potential importance, the thermodynamics of hydration/dehydration reactions in smectite and the connections between these reactions and the fault deformations, is not yet known. These fundamental questions are the heart of the ANR project SMEC of which this internship is part, and which will focus more specifically on the granular modeling part.