Project

Dredging, filling and maintenance dredging for the construction of a submerged tunnel.

Volume : 1.200.000 m³
Location : Cork, Ierland
Client : Cork Corporation
Contractor : Dredging International
Period : May 1996 – March 1999
Contract value : € 12.390.000

Scope of work

Dredging
Submerged tunnel

General Information

In order to solve the problems due to the heavy traffic in Cork it was decided to construct a tunnel that crosses the River Lee downstream of Cork City Centre.

The scope of works under Dredging International’s contract consisted of the dredging of the main tunnel trench and subsequent backfilling with sand and gravel. The contract provided also for restoration of the riverbed profile and the addition of a rock protection layer.

Description of the works

Execution

The trench was dredged in several stages and with different equipment as the material dredged was used for different ends.

Much of the main trench for the Lee Tunnel was dredging by the backhoe dredger “Zenne”. Two barges were used to transport the dredged material some 12 miles downriver and from there to the disposal site four miles offshore.
The cutter dredger “Vlaanderen XIX removed the underlying fluvioglacial material. A second cutter dredger “Vlaanderen XV” was deployed to breach the casting basin bund.

A rock layer, encountered over part of the trench line, was dealt with by the jack-up platform “Zeebouwer”, equipped with the “Hydrohammer system.

The “Big Boss” was employed to remove the rock. This backhoe dredger was equipped with the Backhoover “in effect, a “mini” sweepdredger). This system proved extremely effective in removing very thin layers of recently deposited material immediately prior to immersion of the tunnel elements.

Main Equipment

Trailing suction hopper dredgers “Orwell, Vlaanderen XXI and Vlaanderen XX”
Backhoe dredgers « Zenne and Big Boss »
Cutter suction dredgers « Vlaanderen XV” and Vlaanderen XIX»
Barges DI 68/69
Jack-up platform “Zeebouwer”