Investigation of the dry cracking behavior of coral sand under different gradations and drainage conditions

Desiccation cracking in hydraulically reclaimed coral sand can compromise the stability and service life of island and coastal foundations. To elucidate the governing mechanisms, controlled drying experiments were performed on saturated coral sand specimens of four gradations under drained and undrained conditions. Under undrained drying, fine sand exhibited the most extensive cracking, whereas under drained drying silt was most vulnerable; coarse sand remained largely crack-free in both cases. Fine sand also displayed surface mud films that peeled at critical water contents of approximately 15 % and 13 %. Drainage markedly reduced cracking in coarse-grained samples, a behavior attributed to downward migration of fines and pore-filling effects. Crucially, three-dimensional X-ray computed tomography (X-CT) imaging—applied here for the first time to coral sand desiccation—captured particle redistribution and the internal development of crack networks after drainage and following complete drying. These combined macro- and micro-scale observations advance our understanding of desiccation behavior in calcareous sands and offer new insights for the design, maintenance, and risk assessment of coral-sand foundations in reclaimed island environments.