Carbon Emission Measurement And Reduction Analysis In The Embodied Stage Of Metro Civil Engineering

China is at the peak of subway construction nowadays.In the context of global warming,it's worth studying the characteristics of carbon emission during the subway construction.This study follows the calculation and evaluation pathway for carbon emission based on Life Cycle Assessment?LCA?theory.Firstly,the boundary of carbon emissions of metro civil engineering during the embodied stage are determined.The inventories of carbon emissions of each stage are also determined.Secondly,the embodied three-stage carbon emission measurement model which include production and transportation,construction phase is established.Prefabricated components were increased to estimate in the production and transportation phase.And,labor and the turnover of the turnover materials were increased to estimate in the construction phase.Thirdly,the database of emission factors is developed for the case study by field investigation or adopting authoritative research data.And a metro shield tunnel and an underground station are selected for case study.The carbon emissions of each embodied stage are calculated and analyzed.Finally,the scenario analysis of emission reduction is conducted in which the effects of each approach are calculated and evaluated,and then the effective approaches are recommended.The carbon emissions of the shield tunnel during the embodied stage are calculated and analyzed.The results indicate that the total emissions and intensity are 49799.83t_CO₂ and13.264t_CO₂/m respectively.The emissions of three embodied stages account for 74.1%,1.7%and 24.2%respectively of the total emissions.The production stage of building materials and prefabricated components and construction stage are the key points of emission reduction control.The emissions of tunnel body,end reinforcement and tunnel attached civil engineering account for 91.7%,4.2%and 4.2%,respectively.The tunnel body civil engineering is the key point of emission reduction control.And there are several low-carbon approaches:adopting recycled steel and iron?reducing16.8%of emissions?,adopting recycled concrete?1.0%?,reducing the transportation distance of trashed earth by 5 km?0.4%?,and shifting the soil pressure mud water dual mode to the soil pressure mode?4.9%?.After adopting all the above approaches,the maximum carbon emissions are reduced by 23.1%,and the intensity is declined to 10.192 t_CO₂/m.The underground station which constructed by open excavation is also investigated in this study.Its carbon emissions reach 89814.69t_CO₂ during the embodied stage.Of these,the emissions of the main and attached structure account for 80.9%and 19.1%of the total emissions,and the intensities are 3.482 and 2.575 t_CO₂/m² respectively.And the emissions from three embodied stages account for 87.3%,0.6%and 12.1%of the total amount.The carbon emissions of the main body during the embodied stage were 38.1%from the envelope structure and supporting system project,5.2%from the earthwork and 56.8%from the main structure and waterproofing project.There are several low-carbon approaches for the main and attached structure:adopting recycled steel and iron?32.1%/29.9%?,adopting recycled concrete?2.1%/2.1%?,improving the transportation for earth and stone?1.3%/1.8%?,and improving excavation of earth and stone?0.6%/0.3%?.After adopting the above approaches,the maximum carbon emissions are reduced by 36.1%and 34.1%,and the intensity is declined to 2.227 and1.697t_CO₂/m.The carbon emission calculation model developed in this study can be applied to measuring carbon emissions of the metro civil engineering during the embodied stage.And the results help in quickly estimating the carbon emissions of the entire metro civil engineering during the embodied stage and guiding the actual project to reduce carbon emissions.