Mergor has successfully immersed 5 tunnel elements in the River Shannon in Limerick Ireland

13 November 2008

Mergor has successfully immersed 5 tunnel elements in the River Shannon in Limerick Ireland. All the activities were done according to the schedule and it meets all the quality requirements of the client and Mergor.

The 675m long tunnel is part of the Limerick Southern Ring Road Project. The Ring Road is a Standard Dual Carriageway with a design speed of 100 km/h. The tunnel, has 2 bores and each bore provides 2 lanes. The approximate value of the total Ring Road is €300 million.

Direct Route has employed The Direct Route Construction Joint Venture (CJV) to design and build the new Project. CJV has subcontracted Van Oord UK (VO) to carry out the necessary marine works for the tunnel in the River Shannon. A part of these marine works is the specialized operation of immersing the tunnel elements. This was performed by Mergor (MER) in sub-contract to VO.

The immersed part of the Shannon tunnel consists of 5 tunnel elements each 100 * 25 * 8,5 meter and a weight of 22.000 tonnes. All five tunnel elements were built in a casting basin situated in the Northern Approach. The tunnel elements were fitted with Mergors re-usable steel bulkheads which enabled them to float. The tunnel elements have been transported out of the casting basin into the river Shannon. The elements were immersed in a pre-dredged trench and placed on temporary supports. After sandflow underneath the tunnel elements the temporary supports were released and the element rests now on its final sand foundation. The tunnel is backfilled with sand and a rock protection layer.

During the project Mergor had to stand up to high tidal differences and currents. All the transport and immersion systems were designed for these difficult conditions. The expected tidal differences up to 6 meter and currents up to 1,0 meter per second occurred during the transport and immersion operations and were smoothly handled by the deployed systems.

Mergor would like to thank all people involved with the project for the great teamwork and cooperation to achieve this milestone in the Limerick Southern Ring Road Project.