Abstract: Polyurethane improvement is a novel, eco-friendly, and rapid method for soil improvement. This study aims to evaluate the effectiveness and applicability of polyurethane rapid improvement for calcareous sand in the South China Sea. The optimal gelling time, static and dynamic strength, and permeability characteristics of polyurethane-cured calcareous sand were investigated through unconfined compressive strength tests, static and cyclic load triaxial tests, and permeability tests. The obtained results encompass both mechanical and permeability properties. Notable findings include: 1) the optimum gelling time for the cured samples is 6.5 hours. 2) The cohesion of the cured calcareous sand significantly improves with increasing polyurethane content, while the internal friction angle remains relatively unchanged. The polyurethane calcareous sand cured in sea water maintains a high strength. 3) Increasing the polyurethane content leads to an increased initial dynamic shear modulus of the calcareous sand, but a reduced maximum damping ratio. 4) The permeability coefficient of the calcareous sand ranges around 10^-6. However, upon adding polyurethane (2%-10%), this value decreases to 10^-8-10^-7, demonstrating a remarkable sealing effect of polyurethane.

Key words: calcareous sand, polyurethane, gelling time, mechanical properties, permeability coefficient