Multiscale Experimental Framework for the Characterization of Unstabilized Rammed Earth

Abstract

[EN] The mechanical response of unstabilized rammed earth (URE) depends on a chain of factors spanning from soil composition to compaction conditions and specimen geometry and manufacturing conditions. This paper proposes a multiscale experimental framework for the physical and mechanical characterization of URE, structured around three hierarchical scales¿soil, fabric and specimen¿and demonstrates it on a single soil sample used consistently across more than a decade of experimental campaigns. At the soil scale, mineralogical composition, particle size distribution, Atterberg limits and linear shrinkage are determined. At the fabric scale, Proctor compaction tests establish the optimum moisture content and maximum dry density, and cohesion tests quantify the tensile cohesion of the material. At the specimen scale, monotonic and cyclic uniaxial compression tests reveal that compressive strength is essentially isotropic with respect to loading direction, while stiffness exhibits a pronounced anisotropy, with an anisotropy coefficient of 2.6. A Proctor-based specimen manufacturing procedure is used to reduce the coefficient of variation of compressive strength from 11.8% to 1.8%, demonstrating the critical role of compaction control in result reproducibility. Diagonal compression tests yield a shear strength of approximately 10% of the compressive strength, consistent with the tensile-to-compressive strength ratio commonly reported for URE. The proposed framework highlights the limitations of single-parameter characterization and provides methodological guidance applicable from soil evaluation to full mechanical characterization of URE.