The importance of swellable strips in tunnel segments

The EPDM profiles that are placed between tunnel segments have a significant influence on the lifespan of a tunnel, because they prevent groundwater from seeping in. This is why they are widely used around the world. But more and more tunnel builders are switching to EPDM profiles that contain a swellable strip. In this article we explain why EPDM swellable profiles are a booming business, especially in the Middle East. With BeSealed we also focus on the swellable seals. 

If you look at a cross-section of a classic EPDM profile for tunnel segments, you can clearly see that it consists of several hollow spaces. This allows the EPDM profile to be pressed in during installation of the tunnel segments. This way the tunnel is sealed against groundwater. 

However, during their lifespan, and even during the construction phase, tunnels are subject to small shifts that cause the EPDM profiles to meet with insufficient pressure or even small gaps to appear between the EPDM profiles. This means that groundwater can still seep in. There is also a clear trend towards deeper tunnels, which means that the EPDM profiles must be able to withstand higher groundwater pressure. 

Modern tunnel builders are therefore increasingly using EPDM profiles that incorporate swellable strips. These swellable strips contain a hydrophilic agent that swells naturally when it comes into contact with water. 

When these strips start to swell, tension is restored to the EPDM profile and the joins between the tunnel segments. The tunnel will be watertight again in no time, even if small shifts endanger the watertightness of the tunnel. This swelling does not occur immediately, but with a delay. This means that the swellable strips are not yet activated during the construction phase. 

The Red Line metro in the Qatari capital Doha, a huge tunnel project uses EPDM profiles with swellable strips to connect the tunnel segments. No less than one million meters of swellable strip was used! 

The tunnel builders in Qatar faced an additional challenge, as the groundwater in Doha is extremely salty, which reduces the swelling capacity of the strips. That is why they approached BeSealed, the Belgian manufacturer of swellable strips, to develop a customized strip. We developed a swellable strip featuring increased expansion in salt water with a very high salt concentration, now known as the Superswell Sealing Insert.

BeSealed has developed a selection of revolutionary and patented swelling products that swell after contact with water and are 100% waterproof. We have a wide range of water swellable sealing solutions.