Description of the thesis topic

The CNRS recruit will work at the Institute of Chemistry of Environments and Materials in Poitiers (UMR CNRS 7285) within the HydrASA team. The IC2MP (University of Poitiers) has nationally recognized expertise in the characterization and thermo-hydro-mechanical behavior of natural clayey environments. As part of a CNRS NEEDS-MIPOR program, this multidisciplinary project aims to explore new perspectives for understanding the reactivity of clayey rocks used in deep geological waste disposal. This environment is severely damaged by the excavation of tunnels (EDZ) and hydrogen overpressures linked to the corrosion of waste containers. The induced fracturing and/or diffuse microcracking significantly impact the transfer properties. There is therefore a major challenge in better understanding the self-sealing of cracks in the context of predicting the long-term behavior of underground structures. Hydration of the initially fractured zone allows for fracture closure and hydraulic healing through swelling mechanisms. However, this process remains poorly understood (origin of healing, reopening at the end of the test) and poorly constrained in the presence of multiphysics couplings. A coupled experimental/multiscale modeling approach was proposed as part of the NEEDS MIPOR PACEM project (2025; IC2MP D. Loan) with the aim of better identifying and quantifying the phenomena involved, as well as moving toward robust and predictive modeling. It is a continuation of the MECHE and ARPENTONS structuring projects. The thesis work will address a key obstacle in the context of these three NEEDS MIPOR programs and is supported by all the partner laboratories (ISM/LMV/GeoRessources/3SR/LETIS ASNR). The researcher will focus on advanced experimental studies using 4D imaging to characterize, in great detail, the dynamic swelling/shrinkage processes of clayey materials in model systems that are much more homogeneous and easy than the Callovo-Oxfordian (COx) clays intended for storage or soils. The candidate will work on compacted illite and smectite powders (MX80) saturated with solutions at different ionic strengths, allowing the dissociation of the impact of interlayer swelling mechanisms (i.e., crystalline and osmotic) from those involved in interparticle pores (i.e., capillary and osmotic pressure). In-operando observation in 4D X-ray µtomography will be carried out using an oedometric cell available at IC2MP (Mhamdi Alaoui thesis, 2023). All volumes obtained during the swelling/shrinkage tests will be processed using an in-house enhanced DVC volume correlation approach. This approach will provide a 3D spatialization of the strains in the core of and near cracks potentially created during the shrinkage phase. In this context, the recruited candidate will be responsible for developing the oedometric-type experimental bench, acquiring 4D images (µtomo RX), and characterizing and gaining a detailed understanding of the phenomena involved during the shrinkage/swelling phases. The candidate will be responsible for the following activities:
- Design and implementation of experimental tests on compacted model clay media.
- Careful and detailed preparation of clay samples
- Analysis and understanding of the phenomena involved during the shrinkage/swelling phases through image analysis and digital volume correlation (DVC)
- Supervision of interns (Master's I and II)
- Presentation of results at NEEDS MIPOR project progress meetings and conferences.
- Preparation of reports (bibliographic and progress).

Work Context

Recruited by the CNRS, the doctoral student will be integrated into the HydrASA team at the Institute of Chemistry of Environments and Materials of Poitiers (IC2MP - https://ic2mp.labo.univ-poitiers.fr/). The general theme of the HydrASA team (Hydrogeology, Clays, Soils, alteration) focuses on understanding and modeling transfers in reactive geosystems. These reactive geosystems refer to a wide variety of natural objects with very different characteristic dimensions: clay minerals and their aggregates, clay soil profiles, and large geological systems. The team's main research interests are to connect the different spatial scales involved in these objects and to integrate large time scales. The recruited person will report to the scientific supervisor of the thesis of the HydrASA team at IC2MP.

Constraints and risks

The candidate will be subject to the laboratory's internal regulations regarding all health and safety rules.
Ad hoc assignments in France or abroad are possible.

Additional Information

Candidates must hold a master's degree in geosciences, materials physics, or mechanics. Applicants must:
- be proficient in the physics of clay materials (hydration, mechanics, swelling, porous networks, etc.)
- be able to set up and develop experimental tests
- be proficient in the fine preparation of clay or other materials in the laboratory
- be proficient in imaging techniques (X-ray, SEM, TEM, etc.)
- be proficient in imaging software (3D image reconstruction, image analysis, programming, etc.)
- be fluent in English - be able to write scientific reports in French or even English
- have project management skills
- have a strong interest in teamwork
The successful candidate must have the motivation and enthusiasm to lead the project from small-scale experimental research to the next level. They must be able to work independently and as a member of a multidisciplinary team. The candidate will be curious and enjoy problem-solving and developing new technologies that require creativity, innovation, and personal initiative while respecting imposed constraints.
Interested and highly motivated candidates should send a cover letter stating their interest in this position, a comprehensive CV (including a list of publications, if applicable), and two academic references (including address, telephone number, and email address).