Abstract: A case study is conducted on the EA4 Bid section project in Xiong’an New Area to address the lack of a quantitative basis for low-carbon optimization of shallow-buried utility tunnel construction methods under the “carbon peaking and carbon neutrality” goals. Additionally, a carbon emission calculation model covering labor, materials, and machinery inputs during the construction phase is established based on life cycle assessment theory. Using one linear meter of the utility tunnel as the functional unit, this study compares the carbon emission intensity, emission structure, and environmental impact of the U-shield method and the cut-and-cover method. Furthermore, three evaluation methods—EDIP2003, TRACI2.1, and BEES+—are integrated to comprehensively evaluate the global warming potential (GWP), acidification potential (AP), and eutrophication potential (EP) of the slope protection, main structure, and waterproofing stages. The main findings are as follows: (1) The unit carbon emissions of the U-shield method reaches 17 129.14 kgCO₂/m, which is 68.11% lower than those of the cut-and-cover method at 53 720.60 kgCO₂/m, demonstrating a substantial carbon mitigation advantage. (2) The carbon emissions of the U-shield method are dominated by embodied carbon associated with construction materials. Conversely, the emissions from the cut-and-cover method are mainly attributable to direct emissions from construction machinery, indicating considerable differences in the dominant emission-contributing processes between the two methods. (3) The stage-based environmental impact assessment shows that the U-shield method results in a lower overall environmental burden during the slope support and waterproofing stages. However, during the main structural construction stage, its GWP, AP, and EP are higher than those of the cut-and-cover method because it uses higher-strength materials, shifting environmental burdens from onsite construction activities to upstream material production. (4) Under shallow overburden conditions, the U-shield method outperforms the cut-and-cover method by reducing earthwork excavation, temporary support requirements, and high-intensity mechanized construction operations.

Key words: utility tunnel, shallow overburden, U-shield method, cut-and-cover method, carbon emissions, life cycle assessment, environmental impact assessment