The influence of wetting and drying on the pore size distribution, water retention, compressibility and liquefaction susceptibility of a silty sand

Hydraulically deposited soils and tailings have a high risk of liquefaction due to their compressible and metastable particle and pore arrangements formed upon deposition. Once deposited they may be subjected to drying and rewetting causing unknown changes to the pore geometries and liquefaction susceptibilities. Here a silty sand, deposited hydraulically, is used to investigate how various drying-wetting histories influence pore geometry, compressibility and liquefaction susceptibility. A homogenous sample preparation method involving slurry deposition method is proposed. Surfaces of sublayers within a sample are desiccated prior to placement of subsequent sublayers. The influence of drying then rewetting on the silty sand’s mechanical behaviour is characterised using triaxial and oedometer tests. The respective pore size distributions are studied using mercury intrusion porosimetry and characterised using fractals. The pore size distributions are converted to equivalent soil water characteristic curves (SWCCs) and compared to other data obtained from direct measurement using the filter paper technique. Certain fractal properties of the pore geometries are correlated to compressibility, particularly the compression index () or slope of the critical state line (). The samples which experienced the most significant prior desiccation had the smallest undrained shear strength and the largest compressibility. Samples without prior desiccation had the largest undrained shear strength and the lowest compressibility. The pore analyses revealed prior desiccation reduced porosity and, at the same time, increased the volume of larger pores and decreased the volume of smaller pores. These pore changes were not erased by subsequent rewetting. In the context of SWCCs, the slopes of scanning curves increased and air entry and air expulsion suctions decreased as the amount of prior drying became more significant. No change to the fractal dimension of the pore size distribution was observed. The increased slopes of the scanning curves were found to be linearly correlated with or . In practice, the drying induced pore rearrangement could lead to a stability concern, especially for marginally stable soil or tailings deposits, as larger pores become greater in number in a way that is not reversed by rewetting, likely making the soil or tailings more prone to collapse or liquefaction