The sample preparation technique has been understood to impact soils’ monotonic and cyclic strengths even when same relative densities are achieved. It is understood that soil specimens prepared by different techniques can have different soil fabrics and hence show different behaviour characteristics. While several studies have investigated the impact of sample preparation techniques on the mechanical behaviour of soils, there is still a knowledge gap on how specimen preparation technique affects soil’s erosion and in particular the erodibility of fine particles in internally unstable soils. To enhance our current understanding on impact of specimen preparation on soils’ erosion response, this study applies micro-CT scanning to gain a detailed and accurate understanding of the internal structure of a transitional gap-graded soil prepared with different specimen preparation techniques. A transitional gap-graded soil is characterised as a soil which is geometrically on the borderline of stability, where the size difference between coarse and fine particles is sufficient to fully promote erosion (as in unstable soils) but not small enough to significantly prevent the erosion of fine particles (as in stable soils). Two techniques of under-compaction moist tamping and wet pluviation are employed to prepare the soil samples for this experiment. All samples were prepared with a fine content of 25% and at the same relative density. Initially, the samples were compared under similar conditions to assess erosion progression. Results showed that the erodibility of the soil was significantly influenced by the preparation method. Micro-CT scanning provided insight into how and why the different specimen preparation methods impacted the erodibility behaviour. The results indicated that wet pluviation samples exhibited more isolated and smaller pore connectivity, with narrower channels between pores. In contrast, samples prepared using moist tamping demonstrated larger pore sizes, greater connectivity, and more extensive channels, leading to a higher degree of erosion.

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