Expérimental et théorique
Permafrost consists of a first layer a few meters below the surface, known as the active layer, which freezes in winter and thaws in summer, situated above a thicker layer of soil constantly below the freezing point. The presence and displacement of a solidification front in the soil can cause underground water flows and change the soil structure, leading to the emergence of surprising shapes on the surface. With global warming and thawing permafrost, this type of event will become increasingly frequent, altering landscapes, their ecosystems, and infrastructures. We will start by studying solidification dynamics experimentally in a stack of water-soaked grains. It could be placed between two plates or in a tube. The propagation dynamics of the freezing front will be studied, paying particular attention to the coupling between the displacement of the front, the induced liquid flows, and the movement of the grains. Grain size, initial compaction, thermal parameters will be varied. We will use model grains (ceramic and glass beads) and grains from real soils (clay, silt, sand). The structure of the granular medium when frozen, and after several freeze-thaw cycles, will be studied and interpreted. This work will enable us to improve our understanding of the mechanisms associated with soil freezing and thawing, and thus be able to predict the consequences, ranging from pavement destruction to the overall behavior of permafrost over the coming decades.