# Optimization Design Study of Pipe Curtain Freezing Scheme for Sanya Estuary Submarine Channel
## 6 Conclusions  
This paper presents a study on the Sanya Estuary Passage submarine pipeline curtain freezing tunnel project, employing COMSOL software to develop a three-dimensional numerical transient model for a detailed analysis of the pipe curtain freezing temperature field. By refining the original freezing scheme based on the results of the temperature field analysis, several conclusions have been drawn:  
1. The number of freezing pipes in the strong freezing zone exceeds that in the weak freezing zone, and the average temperature in the strong freezing zone is lower than that in the weak freezing zone, indicating that the number of freezing pipes significantly influences the freezing effect. When the freezing curtain is essentially formed, it is evident that the groundwater flow lines bypass the freezing curtain, suggesting that the freezing curtain acts as a barrier to water flow. Due to the more pronounced seepage flow upstream compared to downstream during the active freezing period (40 days), groundwater flow carries cold from upstream freezing pipes to the downstream area, resulting in a more pronounced freezing effect downstream than upstream. Consequently, optimization of treatment can be applied to the downstream freezing pipes. 2. The original scheme, with a 10 \({}^{\circ}\)C isotherm, completes all inter-circle operations in 14 days. The Optimized Scheme 1 is 7 days slower than the original scheme, while Optimized Scheme 2 is 10 days slower. However, all schemes are within the predetermined design standard of 25 days, thus meeting the design requirements. 3. The original plan calls for permafrost curtains with thicknesses of 5.22 m, 5.05 m, 5.16 m, and 4.67 m in the southeast and northwest. In contrast, the optimized plan reduces these thicknesses to 4.4 m, 4.36 m, 4.34 m, and 4.43 m in the same areas. The optimized plan further reduces the thicknesses to 4.17 m, 4.11 m, 4.34 m, and 4.15 m, with the greatest reduction observed in the east wall (downstream), where the difference between the optimized plan 2 and the original plan 1 is 1.05 m, and between optimized plan 1 and optimized plan 2 is 0.23 m. The most significant reduction in thickness is observed in the east wall (downstream), where the difference between Optimized Scheme 2 and the original plan is 1.05 m, and between Optimized Scheme 1 and Optimized Scheme 2 is 0.23 m. The average thickness of the permafrost curtain on the four sides of Optimized Scheme 2 is 4.18 m, significantly exceeding the design standard of 3.5 m.
4. The freezing effect of permafrost curtains under the arrangement of freezing pipes in the original freezing program is good, and it is safe and feasible in the actual construction, but the number of freezing pipes is used too much, which will improve the economic cost of construction. Therefore, through the comparison and analysis of the two optimization schemes, under the premise of conforming to the design standard, the number of freezing pipes is reduced moderately. However, it will make the freezing curtain inter-circle longer, and the thickness of the freezing curtain will be reduced, but all of them satisfy the design requirements. The comprehensive comparison concludes that Optimized Scheme 2 is preferable. Reducing the use of freezing pipes and improving the efficiency of the freezing method through optimization is important for future underground applications. By optimizing the layout of freezing pipes, construction costs can be significantly reduced, construction time shortened, and environmental impact reduced. In addition, as technology advances, it is expected that future freezing methods will be more efficient, environmentally friendly and applicable, providing strong support for the development of urban underground space and infrastructure construction. Conceptualization, [PERSON] and [PERSON]; methodology, [PERSON] and [PERSON] and [PERSON]. ([PERSON]); validation, [PERSON], [PERSON] and S.Z.