Life cycle evaluation of greenhouse gas emissions of a highway tunnel: A case study in China

Abstract

The purpose of this paper is to evaluate greenhouse gas (GHG) emissions of a Chinese highway tunnel in the life cycle. Life cycle assessment (LCA) method is adopted in the paper. Based on rock mass classification and pavement categories, five different functional units have been proposed for the first time. The system boundaries, processes and assumptions are defined. The study results indicate: 1) the GHG emissions of a double-track four-lane Chinese highway tunnel in 100 years can be up to 375.5 thousand tons of CO2 eq. Cement and electricity contribute to more than 80% of the total emissions in all functional units. 2) The construction stage, operation stage and maintenance stage emit 30.89%, 56.12% and 12.99% of the total GHG respectively. During the construction stage, casting and lining, rock support and road work are the top three GHG emission processes. 3) Rock conditions are discovered to be an important factor of affecting GHG emissions in tunnels. The GHG emissions of the 1-m Chinese highway tunnel are between 82 t to 113 t CO2eq. With the increase of rock mass grades, GHG emissions rapidly rise if the pavement design stays the same. The emission differences among the functional units are mainly from materials. 4) Asphalt pavements tend to generate more GHG emissions than concrete pavement due to the more frequent replacements of asphalt pavements. This paper investigates the influences of rock conditions and pavement types on the GHG emissions of Chinese tunnels in the life cycle, which can provide a scientific reference for policy making of the Chinese government.