In Stockholm, Sweden, one of the world's longest motorway tunnels is under construction. In order for the tunnel to be safe, high demands are placed on all materials included in the project.
A new bypass route for the E4 European highway, Förbifart Stockholm, connects the southern and northern parts of Sweden’s capital. In addition to relieving traffic congestion in the inner city and increasing the capacity of the Stockholm road system; the new link will have 18 kilometers of its 21-kilometer length going below ground in a tunnel to reduce the impact on important natural and cultural environments. The construction period is expected to be 14 years, with the link opening for traffic in 2030.
The tunnel is equipped with high-tech equipment and advanced systems for electricity supply, ventilation, monitoring and traffic control. In order to safely handle water in the tunnel, a unique egg-shaped concrete pipe, alfa Qmax, is laid along the entire distance of the tunnel; a total of 36 kilometers in both directions. The pipes are joined together with oil−resistant seals from Trelleborg.
Stefan Karvonen, businessman-ager at Meag Va−system ab, part of alfa Rör ab, which supplies the pipes, explains that in a road tunnel there won’t be much stormwater, except at the tunnel entrances. However, when the tunnel is cleaned during maintenance, the water used needs to be diverted as does water used to extinguish a fire if it occurs.
“The requirement from the client, the Swedish Transport Administration, is that all pipes must be tight, nothing must leak.
"We have a close collaboration with Trelleborg and good delivery conditions."
Stefan Karvonen, Meag Va-system AB
In addition, oil−resistant seals are specified in case of oil leakage in the event of an accident,” Karvonen says.
The unique oval shape, like a standing egg, which is narrow at the bottom and top, and wide in the middle, gives the pipe superior self-cleaning ability with small flows of water, while also being able to handle large flows.
Alfa Rör has been working with Trelleborg since the 1970s. The integrated sealing joint in the concrete pipe sleeve was developed by the companies in a collaboration during the 1980s, and the solution has since become the market leader and used in many projects around the world.
Förbifart Stockholm is an extensive project, and all material must be supplied exactly when the contractor demands it. This places high demands on reliable delivery from all subcontractors.
“The pipes are not a stock item, so we manufacture them when customers place orders. When we are going to cast the pipes, we have to have the seals available so they can be cast-in-place in the concrete pipes. We have a close collaboration with Trelleborg and good delivery conditions,” says Karvonen.
Choose the right one and extend life
ALFA Qmax is a joint-proof unreinforced concrete pipe with egg-shaped cross sections. The egg-shaped cross section allows the pipe to have better self-cleaning ability (the narrow part is turned downward) at small flows compared to round pipes, while the pipe can also handle large flows in the wide upper part.
Trelleborg 103 is a pipe sealing system where the seal is cast into the pipe socket in the manufacture of concrete pipes and complies with all European standards.
It is manufactured in oil-resistant rubber, Nitrile Rubber (NBR), and Ethylene Propylene Diene Rubber (EPDM).
Gudrun Uhlmann, Sales Manager at Trelleborg, explains that it is important to choose the right type of rubber material for different applications, to ensure a long service life.
“EPDM is usually the most suitable rubber material for pipe seals, but in the Förbifart Stockholm project where one can expect the influence of oily water on some parts of the route during the tunnel's operation, oil resistant NBR seals are more suitable. With a long-term resistance to mineral oil, NBR gives a longer service life. This is good for the environment and the pipes are kept tight for a longer time. The application uses integrated seal, PG joint
(Prefabricated Glide) joint, reducing the risk of the assembly being in-correct,” says Uhlmann.