Méthodologie de caractérisation et de formulation des sols pour la construction en terre: approche basée sur la fraction fine

The transition toward low-carbon construction materials has renewed interest in earth-based techniques, yet their widespread adoption remains limited by the high variability of soils and the lack of simple, reproducible characterization procedures. This doctoral research proposes a multi-scale methodology to identify the key parameters governing cohesion, workability, and mechanical performance of earthen materials, with a focus on the fine fraction (< 400 μm), recognized as the most active component of soils. Four contrasting soils were analyzed through geotechnical, mineralogical and physico-chemical testing. Results show that clay mineralogy, adsorption capacity, and Atterberg limits strongly influence both fresh-state behavior and hardened mechanical performance. A formulation method based on consistency limits was developed and validated on earthen mortars, establishing robust relationships between water content, flow spread, shear yield stress, and plastic viscosity. Compression tests on compacted cylinders and compressed earth blocks (CEB) further confirmed the transferability of laboratory-scale observations to material and product scales. The study demonstrates that the fine fraction is a reliable indicator for predicting density, cohesion, and mechanical resistance of earthen materials. These findings pave the way for simplified and more accessible soil suitability assessment protocols, supporting the deployment of low-carbon earthen construction in modern building practices.