Shannon Tunnel

• Client: John Sisk and Sons
• Contractor: Direct Route
• Market Sector: Highways
• Services: Civil Engineering

The immersed tube tunnel crossing the river Shannon in Ireland, required the construction of large temporary cofferdams on either bank of the river to allow the precast concert tunnel units to be floated out through the tidal defences into the river.

MLM gave design and checking assistance to John Sisk and Sons, who where part of a consortium designing constructing and operating a new Immersed Tube Tunnel under the river Shannon, as part of a bypass to Limerick in Ireland. This involved complex stability analysis of the cofferdams under transverse and longitudinal loads at the many different stages of their construction and use.

The challenging features of the design were:

• Large size of Cofferdams: 110m long x 31m wide x 17m deep
• Poor ground conditions: soft alluvium overlying limestone
  bed-rock
• Very complex sequence of construction
• Frequent design changes, to the temporary works, to assist the other consortium members in the programming of their work