The Corrib pipeline tunnel being excavated in County Mayo is nearing completion, with breakthrough expected in the coming months.
Once built, the 4.9km tunnel will be longer than the Dublin Port Tunnel and it will also be the longest gas pipeline tunnel in Europe.
The joint venture contractors building the Corrib tunnel are BAM Civil along with Wayss & Freytag. The joint venture brings together tunnelling specialists from Germany with civil engineering expertise from Ireland. The tunnel construction crew comprises three shifts of eight people each, and works 24 hours a day, seven days a week, with regular stoppages for equipment inspections and interventions.
Two small locomotives support the tunnel-boring machine called ‘Fionnuala’, which passed the 4km mark in recent weeks. “These small trains are essential for ensuring that the supply of personnel and materials remains uninterrupted,” according to Kieran White, a tunnel engineer with Shell E&P Ireland Limited.
Excavation of the final section of the tunnel is expected to be slow, as the tunnel-boring machine will be boring through the rock. Regular inspections of the cutter head will be conducted, with cutting tools exchanged as required. “When tunnelling commenced at Aughoose, County Mayo, in early 2013, the tunnel-boring machine encountered rock almost immediately, so we now know what to expect now as we approach Glengad,” explained Paul Hughes, Shell E&P Ireland Limited’s tunnel construction manager.A special twin-track ‘California Switch’ was installed at 2.5km, which allows for trains to pass each other within the tunnel. Almost 25,000 concrete segments, which are produced in County Westmeath, are required to build the tunnel. Approximately 140,000 tonnes of material have been excavated since the tunnel operations commenced.
Once the tunnel is built, the process of installing the gas pipeline and its associated services inside the tunnel will get under way. The first gas from the Corrib field is expected to be delivered into the national grid during 2015.