Stockholm, one of Europe’s fastest growing cities, is expected to a population of more than 2.5 million by 2030.To manage the ever-increasing road congestion that accompanies population growth, large investments are being made to improve transport infrastructure.
One such improvement, the Stockholm Bypass, is a new motorway linking southern and northern Stockholm and creating a new route for the European E4 highway past Stockholm. Many alternatives have been studied for a new link west of Stockholm. To reduce the impact on sensitive natural and cultural environments, 18 km of the total 21 km of the motorway link will be via a road tunnel.
WSP* has been involved throughout the design and construction of the project, providing multi-disciplinary expertise including geotechnical, rock mechanical, geological, hydrogeological and environmental investigations, design of temporary constructions, rock portals and soil reinforcements, BIM modelling, tender documents and site supervision during the construction phase. We have also installed instrumentation for ongoing monitoring.
The tunnel will be passing three times below the Lake Mälaren and at one point as far as 100 m below the level of the water table. This has made the Stockholm Bypass the largest rock fissure grouting operation undertaken for a road tunnel in Sweden. The bedrock in the Stockholm area provides generally good conditions for underground construction. However, some sections of this project that pass through fault zones presented grouting challenges. WSP*’s team of rock grouting engineers developed a strategy to seal the tunnel and provided grouting support during construction. To control the water hazards in the fracture zones, our team tackled the challenging conditions using a combination of design and observation methodology.
An important challenge for the project’s sustainability was appropriately managing contaminated soil. Soil excavated from traffic points and connections above ground had the potential for contamination due to previous industrial land use. WSP* developed a strategy for the environmental investigations and for handling contaminated material during construction. We also developed site-specific guideline values for the contaminated soil management plan. Our strategy included consideration of the different protected areas along the route, how people may be exposed to contaminated soil, how groundwater could be affected, and how contamination may spread. For greater sustainability, the intent was to reuse less-polluted soil close to the site excavation in order to reduce the amount destined for landfill and avoid the associated transport.
The Stockholm Bypass is expected to take approximately 15 years to complete. When operational, it is estimated that it will carry more than 140 000 vehicles per day, enabling safe, reliable and smooth travel with less congestion and disruption, thereby contributing to the ongoing livability of this growing city.
* This work was performed by Golder professionals who joined WSP in an acquisition completed in 2021.