Experimental investigation on the stiffness and shear strength of polymer-cemented calcareous sand

Calcareous sand, as the marine biogenic sediment, plays a critical role in coastal infrastructure construction for island and reef engineering projects. However, its high compressibility and particle fragility properties probably lead to structural instability in constructed facilities. This study employed polyurethane foam adhesives to enhance the mechanical performance of calcareous sand foundation, which offers advantages such as short curing time and significant strength improvement. The shear response and cementation mechanism of polymer-cemented calcareous sand were investigated. The test results revealed that the shear strength of calcareous sand markedly increased with the polymer content. The polymer significantly improved cohesion but minimally affected the internal friction angle of calcareous sand. It is implied that the overall shear strength enhancement basically originated from the contribution of cementation. At large strains, the measured results showed that different critical state lines exist for both uncemented and cemented sands. These findings suggested significant complexity in revealing fundamentally different behavior between uncemented and cemented sands. The cementation predominantly derives from polymer-induced cohesion enhancement through particle encapsulation and inter-particle void filling, while maintaining the original frictional characteristics. The micro-observation and macro-behavior provide fundamental insights for optimizing polymer-cemented calcareous sand foundations in coastal infrastructure projects.