Limerick Tunnel wins 2008 Fleming Award
28 Jan 2009

The Limerick submerged tube tunnel temporary works project has won the 2008 Fleming Award. DirectRoute Ltd (John Sisk & Son Ltd are part of this consortium), geotechnical consultant Webber Associates, part of Coffey Geotechnics and structural consultant MLM Consulting Engineers were awarded the £3,000 prize in December.

Their winning presentation described the design and construction of the temporary works for the southern cut and cover and northern float-out sections of the Limerick Tunnel.

On the southern side of the River Shannon, the scheme involved building a cut and cover section inside a retained excavation 130m x 30m and up to 11m below datum (ground level). On the northern side the float-out section also comprised a retained excavation 130m x 30m, in this case up to 15m below datum. In addition, the river ends of the excavations were exposed to high tide levels up to 3.5m above datum.

The southern cut and cover section was excavated under water. Considerable problems were experienced with siltation before placing the base slab underwater so it was decided to excavate the northern float-out section in the dry. Previous analysis had indicated that excavation in the dry would lead to excessive wall moments, even with the use of temporary struts at intermediate levels.

However, a successful method was devised, in which ground level was first lowered by 2.5m outside the wallls to reduce the loading on them.

You can read more information on the Limerick Tunnel Project at www.limericktunnel.com