A Systematic Methodology for CO2 Accounting and Sustainability Assessment in Mechanized Tunnel Construction

Tunnel projects are key to modern transport infrastructure, with growing focus on ecological sustainability. Considering global climate goals and stricter regulations, systematic CO2 emission recording and optimization are vital. This paper presents a methodology for assessing sustainability in tunnel construction, especially mechanized tunneling with tunnel boring machines (TBMs). It combines Life Cycle Assessment and the Greenhouse Gas Protocol, tailored to tunneling projects. The approach captures emissions from material production (particularly concrete and steel), TBM operation, ventilation systems, and transport processes. Validated by expert surveys and literature, the methodology addresses gaps in CO2 accounting. An example project with two 3 km tunnels shows material production causes over 90% of emissions, while transport and machine operation contribute about 8%. This highlights optimization potential via low-CO2 cements, steels, and efficient segmental lining designs. The methodology aids planners, builders, and public clients in ecological assessment and can be adapted to project needs. It supports early-phase emission reduction decisions and may be transferred to other infrastructure projects, guiding sustainable development despite challenges like data complexity and the need for standardized emission values. Keywords: Sustainability in tunnel construction, CO2 accounting, mechanized tunneling, life cycle assessment, infrastructure projects