Comparative Climate Assessment of Alternative Tunnel Construction Scenarios: A case study of a service tunnel in the Otterhällan subproject, part of Västlänken

Abstract

The construction and civil engineering sector accounts for approximately 20 percent of Sweden’s total share of greenhouse gas emissions. These may involve road and rail infrastructure which contribute both through emissions from traffic and production of materials and construction activities. Trafikverket has therefore set national goals to achieve a climate neutral infrastructure by year 2040, with interim reduction targets along the way, such as a reduction of 60% by 2030. The aim of this study is to analyze how the choice of materials can influence the climate impact in a tunnel production process, by focusing on a case study within the Västlänken project, service tunnel 202 in the sub project Otterhällan. The study was carried out through a scenario-based comparative analysis using Trafikverket’s climate tool, Klimatkalkyl, Environmental Product Declarations and project specific data. The optimized scenario resulted in the lowest climate impact, with a reduction of 30 percent compared to the reference scenario, which was insufficient to meet Trafikverket’s climate target for 2030. The results also show that shotcrete and rock bolts account for the biggest emissions in the tunnel, where cement- and steel-based materials dominate the climate impact. Furthermore, the results highlight that using 4D-reinforced shotcrete instead of 3D result in a reduction of emissions by 4,3-tons CO₂ with no additional cost, while using PC-bolts instead of rebar bolts result in a reduction of 9,3-tons CO₂ and a 92 percent increase in material cost, despite the rebar bolt being made of recycled steel. Simultaneously, PC-bolts contribute to a safer working environment and a reduction of 41 percent in labor, machinery and CO2-related costs. The results therefore highlight that climate optimization should be balanced out with cost and feasibility aspects. Additionally, material optimization alone is unlikely to achieve future climate targets, highlighting the need to integrate technologies targeting the production process of cement and steel, such as CCS and HYBRIT, in order to decrease carbon emissions more effectively.