Impact of stress paths on erodibility in gap-graded soils: the critical role of geometric criterion in the soil on the borderline of stability

Abstract Suffusion, one of the most intricate forms of internal erosion, plays a critical role in the failure and instability of embankment dams, levees, and other hydraulic structures. While recent experimental research has provided new insight into suffusion, the experiments are mainly conducted under controlled stress environments that do not necessarily reflect the complex stress conditions found in real-world applications. In field settings, soils experience a range of stress paths due to factors like loading cycles and construction activities which impact the soil structure. These varied stress paths affect the soil’s pore structure and grain interactions, which in turn can significantly influence the erosion behaviour of fine particles. In this study, a modified hybrid erosion-triaxial apparatus was developed to examine the impact of different stress paths on the erosion behaviour of three soil categories: stable, unstable, and on the borderline of stability. The results indicate that for fully stable and unstable samples, the erodibility of fine particles remains unchanged regardless of the stress path. However, it was shown that the samples on the borderline of stability exhibited different erosion behaviours. It was demonstrated that for this sample, a closer attention is needed considering the simultaneous effects of changes in geometric conditions and the role of fine particles within the soil structure. The results indicated that for the geometrically transitional sample in near-underfilled conditions, the impact of stress states on the soil’s erosion behaviour becomes negligible when hydraulic forces are sufficiently large.