Toward continuous shrinkage measurement of poured earth: practical setup and underlying shrinking mechanisms

Abstract Continuous shrinkage measurement in earth-based materials remains technically challenging, particularly for high-water-content mixtures with low initial stiffness. In this study, a semi-cylindrical experimental setup, combined with digital image correlation (DIC) for measurements of surface strains and a linear variable differential transformer (LVDT) for interior strains, is proposed and validated to track the shrinkage behavior of pourable earth materials. Mass loss, surface temperature, and capillary pressure were simultaneously measured and compared with those of conventional prismatic specimens. Both geometries exhibit comparable drying kinetics under identical environmental conditions, with an initial constant-rate period (CRP) followed by a falling-rate period (FRP). However, the semi-cylindrical geometry yields a shorter CRP and enhanced moisture uniformity across the drying depth, attributed to a higher surface-to-volume ratio. During the CRP, shrinkage increased linearly with the volume of evaporated water. In the FRP, shrinkage in both geometries followed the Biot–Bishop effective-stress framework. Although some degree of differential shrinkage remained within the semi-cylindrical specimen, the deformation measured in the interior corresponded more closely to macroscopic water loss, demonstrating that LVDT measurements allow tracking in a simple and practical manner the bulk shrinkage behavior during drying.