Abstract: In the construction process of underwater and high water pressure large-diameter shield tunnel connecting channels, the design and construction face numerous challenges due to the lack of sufficient engineering technical standards and case experience. To address these issues, case study is conducted on six connecting channels of Haizhuwan large-diameter shield tunnel in Guangzhou, China, to explore a more applicable construction scheme. First, an in-depth analysis of the engineering geological supplementary investigation data and on-site construction conditions is conducted to reveal the deficiencies in the original mining method design and construction scheme. Then, two optimized schemes, mining method combined with ground freezing reinforcement scheme and mechanical pipe jacking construction scheme, are proposed. Thereafter, a comprehensive optimal selection analysis of different construction methods is performed in terms of safety, cost-effectiveness, and construction period, and carbon emission indicators are introduced for green and low-carbon assessment. The results show that the mechanical pipe jacking method is superior in safety and construction efficiency to other schemes, significantly shortening the construction period; and the carbon emissions are reduced by 2 747.51 tCO_2e compared to the mining method combined with ground freezing reinforcement scheme.

Key words: large-diameter shield, underwater connecting channel, ground freezing method, mining method, mechanical pipe jacking method, carbon emission calculation, scheme comparison