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Renewing the slide rails at the Leer Sea Lock


Renewing the slide rails at the Leer Sea Lock

Use of a mobile caisson

Caisson specifications:

The caisson, built by Hebold in Cuxhaven, consisted of a semi-circular pipe with an overall diameter of 4500 mm. The pipe was made of 4 individual segments each 2500 mm in length and a tunnel 1800 mm in length. The total length of the caisson was approx. 11,500 mm. The entry shaft was 8000 mm high and its diameter was 900 mm. The airlock was 2000 mm high and had a diameter of 1800 mm. The total weight of the caisson was approx. 28,000 kg.

The task:

The Seeschleuse Leer consortium, which consisted of Bitek Bergungsdienst GmbH and Nordseetaucher GmbH, won a contract in 2001 to renew the slide rails at the Leer sea lock.

The job comprised removing all the old rails and mounting new rails on the existing support for the lock gate.

As the foundation was in very poor condition, we also had to renew the concrete and all reinforcements.

One of the main difficulties of the project was that shipping had to continue; the lock had to be open at certain times to allow ships to pass through, meaning that we were unable to work continuously. The lock would be blocked to allow us to work for approx. 70 hours at a time and we then had to clear the site to enable vessels to pass.


The caisson has a displacement volume of 97 m³. The volume of the lower airlock section was 41 m³, equalling a displaced seawater weight of 143,520 kg.

Work carried out:

Demolition of concrete structures and foundations:

The weak foundation and the supports of the old rails had to be removed. To do this, we constructed a miniature caisson for a remotely controlled miniature excavator as there was no other feasible way of getting the excavator into the caisson and back out again. The debris was filled into sacks and brought to the surface by divers.


Cavities had been detected in the foundation and it was our task to fill these cavities. To do this we injected approximately 350 litres of dual component foam into the cavities.


Once we had completed the demolition of the concrete, all surfaces were cleaned, the supports for the rails were built and all the necessary reinforcements were installed.

Inside the caisson there were two separate pipes for concrete; special concrete was pumped through these pipes.

After this stage had been completed, the new slide rails were laid by divers and secured. The construction work was supervised by KMT Engineering, Hamburg.

The caisson was classified by Germanische Lloyd.