Optical shrinkage curve characterization as a tool for assessing cyclic wetting-drying effects on hydraulic conductivity of fine-grained soils

Institute for Geotechnics Leipzig, Leipzig UAS, Germany

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Abstract

Understanding shrinkage behaviour in soft soils is essential for assessing structural and hydraulic stability under environmental stress. This study applies a shrinkage-curve-based method to evaluate soil behaviour before and after cyclic wetting-drying. The main objective is to identify how structural integrity influences shrinkage response and hydraulic sensitivity. Shrinkage curves were generated using a novel high-resolution optical volume measurement system, enabling continuous monitoring of volumetric changes during drying. Hydraulic conductivity and shrinkage tests were performed on representative fine-grained soils exhibiting varying fines contents both prior to and after controlled wetting-drying cycles. The wetting was performed using a capillary suction method, while drying occurred under controlled room temperature conditions, replicating the natural wetting and evaporation processes observed in the field. Derived shrinkage parameters were correlated with hydraulic conductivity before and after 5 wetting-drying cycles. This correlation provides a quantitative link between mechanical deformation and hydraulic evolution across different soil conditions. If changes occur during the residual shrinkage phase, results suggest these may be reflected in more pronounced increases in hydraulic conductivity following consecutive wetting-drying cycles. The post-cyclic shrinkage curves are used to validate these observations, indicating the link between structural degradation and the rise in hydraulic conductivity. These findings emphasize that cyclic wetting-drying induces irreversible changes in density and microstructure. The proposed methodology provides an efficient way to predict post-cyclic soil behaviour, eliminating the need for resource-intensive repeated long-term testing, contributing to improved evaluation and design of hydraulic barriers and other soft soil infrastructures.