The compressibility and shear strength of soil play a crucial role in engineering design and construction. For this study, samples were collected from the indoor geotechnical tests conducted on the fourth layer of the third series of the Haikou Formation. By conducting a correlation analysis of various physical properties of soil and utilizing the random forest algorithm, we developed a predictive model for the compressibility and shear strength of coastal soft soil. Initially, we proposed an empirical formula that utilizes mathematical statistical analysis methods to characterize the correlation between the indicators of this soil. Subsequently, we employed the feature selection guided by the aforementioned data analysis results to establish a random forest model. This model predicts the compressive modulus, compressibility coefficient, cohesion, and internal friction angle of the soil. The results indicate that the established model exhibits strong predictive capabilities, with the mean squared error values of compression modulus (0.012), compression coefficient (1.21× 10⁻⁶), cohesion (0.081), and internal friction angle (0.003). The data analysis methods, fitting parameters, empirical formulas, and random forest model employed in this study hold substantial value in guiding the preliminary evaluation stage of engineering projects with limited data. This study helps to save time and cost of geotechnical investigation for soft soils in the area.

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.

In order to alleviate the problem of grouting blockage caused by the immediate action of bacteria and chemical reagents in the process of MICP reinforcement of sandy soil, this paper delays the generation rate of calcium carbonate by adding urease inhibitor AHA to the cementing solution and lowering the pH of the bacterial solution. The mechanism of action of the two methods was explored, and their effects were compared and analyzed. The results indicate that both AHA method and low pH method can effectively delay the generation rate of calcium carbonate and improve the reinforcement effect of MICP under different mechanisms of action. The reinforcement effect is best when the AHA content is 0.1% or when the pH drops to 5.5. Comparing the two methods, it was found that the solidification effect of low pH method on sandy soil was slightly higher than that of AHA method. This is because the calcium carbonate crystal size generated by low pH method is smaller than that of AHA method. Under similar calcium carbonate content, the smaller the crystal size, the more bonding points between calcium carbonate and soil, and the higher its strength. Exploring the mechanisms of action of the two methods, it was found that the AHA method delays the rate of urea hydrolysis catalyzed by urease. The low pH method acts on the binding process of carbonate ions and calcium ions after urea hydrolysis, as well as inhibiting urease activity. The two methods have different mechanisms of action, but both can achieve the goal of delaying the rate of calcium carbonate formation.

The Sanya estuary passage project is the latest and highly technical underground project after the large shield underground construction, which is of great significance to the construction of the Hainan free trade port and underground space construction innovation. In this paper, we use finite element software to analyze the deformation, stress, and surface settlement of the pipe curtain structure during construction under two conditions (original riverbed line and maximum scour riverbed line) in order to provide guidance for the actual project. Numerical simulations show that due to excavation and unloading, the bottom and top of the pipe curtain structure are subject to tensile stress; the bottom rises, the top settles, and converges in the horizontal direction; under the original riverbed line condition, the displacement values of each index are larger; changing the riverbed line does not change the maximum and minimum main stress of the pipe curtain structure significantly, and the stiffness of the pipe curtain structure can meet the maximum water level and the maximum scour in two unfavorable conditions; the pipe curtain structure can meet the structural. The pipe screen structure can meet the structural load‐bearing requirements. Suggestions for the design and construction of the project: strengthen the thickness of the pipe curtain at the side wall position, that is, use larger diameter steel pipes; do a good job of antiseepage and anticracking of the concrete at the corner of the pipe curtain structure and the side wall position during the construction process.

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.