Insufficiency of immersion joints in existing immersed tunnels

Abstract

In 2009 and 2010, two leakages through immersion joints occurred in the First Coen Tunnel near Amsterdam. From the study on t-he cause of these leakages, it followed that there was a potential problem for existing immersed tunnels: failure of the temporary Gina-seal combined with corrosion on the clamping structure of the definitive Omega-seal. It is unknown whether the immersion joints of existing immersed tunnels in the Netherlands will still function during the remaining design lifetime. There is lack of calculations on the governing watertight parts (Gina-seal and Omega-seal) in immersion joints. The main goal of this research is to become both qualitative and quantitative insight into the watertightness of existing Gina-seals and Omega-seals in immersed tunnels. It is applied to the Kil Tunnel (case study).

Leakage through immersion joints can only take place when both the Gina-seal and the Omega-seal fail. The Gina-seal consists of a rubber gasket (the Gina-gasket) and a clamping structure that connects the Gina-gasket with the tunnel element. It can fail due to widening of the joint (due to seasonal temperature changes) combined with relaxa-tion, increased soil pressure and differential movements of the tunnel elements. The Omega-seal consists of a rubber gasket (the Omega-gasket) and a structure that connects the flange of the Omega-gasket with both tunnel elements (the clamping structure). It can fail if the clamping structure is affected by differential movements, relaxation, corrosion and widening of the joint (due to seasonal temperature changes).

The Kil Tunnel (case study, finished in 1977, below Dordtsche Kil) consists of 3 tunnel elements, so it has 3 immersion joints (1A, 2E and 3A). Immersion joint 1A and 2E connect the tunnel to both abutments and are exactly the same. Immersion joint 3A connects two tunnel elements to each other. The Gina-seal and the Omega-seal are slightly different for 1A/2E and 3A.

The Gina-seal has to meet several requirements in order to be watertight. The result of the case study on the Gina-seal in the Kil Tunnel is the following:
- Joint 1A/2E may not meet Requirement G2 roof (Force equilibrium in the roof). This check requires attention. Therefore, it is recommended to do visual inspections in the roof of joint 1A/2E. All the other requirements are met with large margins.
- Joint 3A meets all requirements with large margins. It is expected that this Gina-seal fulfils its function over the entire lifetime.
- It is recommended to measure the value of maximum difference between winter and summer of the immersion joint in longitudinal direction (Δx) in all immersion joints.

The Omega-seal has to meet several requirements in order to be watertight. The result of the case study on the Omega-seal in the Kil Tunnel is the following:
- The compression of the flange of the Omega-gasket (cO) determines strongly whether the requirements on watertightness are met. When the compression of the flange of the Omega-gasket is smaller than 5 mm, the requirements are not met. This means that leakages through the immersion joint can occur. It is recommended to measure this value.
- The maximum allowed penetration depth of the corrosion is 2 mm of the core of the bolt. If this value is exceeded, the functioning of the bolt is not guaranteed anymore. It is recommended to remove a bolt at the “splash zone” in order to see how far the corrosion has penetrated the bolt. Besides, it must be checked whether the corrosion is an on-going process.
- When one bolt fails, the clamping plate will deform. As a result the forces on the adjacent bolts will be lower. It depends on the state of the bolt whether this is able to take the loads. This will determine whether the ‘zipper effect’ will occur.

This study has created a theoretical description of the state of existing Gina-seals and Omega-seals. However, visual inspections and measurements are also needed to judge whether the seals will function during the remaining lifetime.