Calcareous sand, characterized by numerous pore spaces, easy fragmentation, and low strength, is commonly used as fill material in island construction projects. Due to these limitations, it often fails to meet the requirements of actual engineering applications. This paper uses oxidized graphene in combination with fly ash cement to modify calcareous sand. The effects of oxidized graphene, fly ash cement, and curing time on the modification effect were investigated through triaxial tests and numerical simulations. The experimental results show the following: (1) Both the extension of curing age and the increase in the dosage of fly ash cement can improve the shear performance of calcareous sand, with the increase in the dosage of fly ash cement able to ensure thorough bonding between calcareous sand particles. (2) Graphene oxide can significantly improve the shear performance of calcareous sand cement mortar, with the optimal dosage being 0.06%. Excess amounts result in a reduced performance improvement, which is related to the degree of the catalysis of oxidized graphene on hydration reactions. (3) The numerical simulation shows that when the maximum shear stress reached 3437 kPa, cracks began appearing on the specimen, consistent with the experimental results. Meanwhile, the numerical simulation results reveal the crack propagation pattern in the specimens, showing that the stress at crack initiation is lower than the peak stress.

This paper takes the freezing project of the North Arch Tunnel of the Hong Kong–Zhuhai–Macao Bridge as an example. Based on Darcy’s law and the theory of heat transfer in porous media, using the coupled module of the temperature field and seepage field in the COMSOL Multiphysics software, numerical simulations of the freezing reinforcement of the new pipe curtain freezing method are conducted to study the influence of different factors on this method under seepage conditions. The research shows that an increase in the groundwater flow velocity will affect the development of frozen soil curtains, prolonging the formation time of frozen soil curtains. A rise in the initial ground temperature will increase the time required for the formation of frozen soil curtains during the freezing process, resulting in a slight increase in the temperature of the final frozen soil curtains. With an increase in the salinity of the groundwater, the temperature at the temperature measurement point upstream of the freezing pipe increases, while the temperature at the temperature measurement point downstream of the freezing pipe decreases. The average temperature of the frozen soil curtain also increases with an increase in the salinity of the groundwater. This study is expected to provide a valuable reference for similar projects in the future.