A JACK-UP barge more than doubled drilling production at the Dublin Port Tunnel despite being a fish out of water.
Howard Marine's Zee Jack Skipper, designed for over-water operations, was used on advance works inside the huge TBM launching shaft at the suggestion of Japanese tunnelling contractor Nishimatsu Construction.
Nishimatsu, part of the joint venture building the tunnel, was having problems supporting the horizontal drilling machines creating the tunnel portal in the shaft wall.
It felt a height-adjustable jackup barge was the solution.
Because the barge was designed specifically for over-water work, Howard Marine first wanted to ensure it would function satisfactorily as a drilling platform.
As well as being loaded by the drill rigs and equipment, the barge had to withstand lateral forces caused by horizontal drilling. After discussions with Nishimatsu, Howard Marine carried out calculations and testing on the rig and was satisfied the idea would work.
A large crane lowered the barge into the shaft where it was set to work, hydraulically raising and lowering itself for drilling at various levels. Lateral forces were overcome by using tie bars connected to pre-drilled rock sockets in the tunnel face.
Although the barge was jacked up as much as 12m to 14m from the ground, it did not move laterally, Howard Marine said.
The jack-up not only provided a safe working environment for the drilling crews, it more than doubled drilling production.
The Dublin Port Tunnel project is jointly funded by the Irish government and the European Union. It is being built by joint venture contractor NishimatsuMowlem-Irishenco for the Dublin Corporation.
The 4.5km long twin bored tunnel will link to the M1 across the River Liffey and with the orbital M50, bypassing the city centre.