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Down in a large port

Ports and harbours Ireland

Construction of the biggest fishing port in Europe is under way in north west Ireland. Diarmaid Fleming braved the Atlantic breeze to report.

Killybegs reeks of fishing. The smell of processed fish hits the nostrils before you approach the town and the harbour bristles with fishing trawlers. Despite being located in beautiful scenery, there is an air of industry and bustle about the town giving a feeling that if your business is not fish, you have little reason to be in Killybegs.

Situated in County Donegal on Ireland's north west Atlantic coast, the harbour is the country's premier fishing port accounting for one third of all the Republic's fish landings.

Around 80,000t live weight was landed last year. Even though this is a big reduction on the 170,000t landed in 1995 before EU fishing quota cuts, the Irish government has sanctioned the largest ever marine project in the country.

'The quotas have reduced but upgrading work at the harbour was absolutely essential. Vessels are getting much bigger - the present harbour was designed in the 1960s for the smaller vessels of that era. Major investment was needed for the huge vessels of today, ' says Department of Communications, Marine & Natural Resources assistant chief engineer John McHale. The Department owns and operates the harbour along with four other key Irish fishing ports.

The new supertrawlers, or motorised fishing vessels, based at the port are huge ships; the mammoth Atlantic Dawn at 145m long is the biggest trawler in the world. Increased berthing capacity was needed at the harbour, as well as new unloading and processing facilities to cope with their massive haul.

'We have around 1,500m of vessel length vying for 605m of available berthage with drafts - the depth of water in which the ship floats - of 4.4m to 7.6m in depth, and only 153m of 7.5m draft at low water, ' McHale says.

Construction of a new facility on the seaward side of the existing berth was selected for the new development, rather than extending or building around the old facility. Moving outside offered environmental benefits by keeping the unloading as far away from the village as possible, while enabling easier future expansion.

The Department's consultant Kirk McClure Morton carried out extensive wave studies and modelling to develop the arrangement of the quay. This work was needed for environmental as well as engineering reasons. Extending seaward meant extensive land reclamation, along with dredging to provide water depths up to almost 12m at low water. A dog-leg arrangement on plan provides two new berthing faces of 150m and 300m, enclosing a reclaimed area of 11ha. The arrangement was adjusted to find the optimum trade-off between dredging and reclamation.

Around 320,000m 3of material arose from dredging. 'The dredging provided around 230,000m 3of gravels and clays, which was suitable for use as fill in the reclamation. We started the reclamation by building a rock bund on the existing material to work off, and then built a series of 'spine roads' on the existing material, dividing the area into cells, ' says contractor John Mowlem Construction director Bill O'Regan.

The remainder of the dredged material - around 100,000m3 of silt - was unsuitable as fill and was dumped at a licensed sea site by Irish Dredging.

The dump site, 15km away in 70m of water, was chosen after detailed environmental studies and consultation with local fishermen, as well as wave modelling. Stringent environmental impact standards apply on the job with marine habitats and fish farms nearby.

Geotextile membranes prevent leaking of fines from behind the bunds retaining the fill material, with turbidity levels regularly monitored during reclamation.

Around 270,000m3 of rockfill was imported from local quarries to provide the remainder of the fill, piled 3.5m above its final level to provide a surcharge for compaction. The sands and gravels compact quickly, with little movement after around 25-30mm in the first two weeks.

The 350mm thick C50 reinforced concrete structural ground bearing deck slab is designed for a whopping 75kN/m2 live loading - well in excess of standard highway loading - and can take outrigger point loads of 200t.

The high loading capacity is in anticipation of future offshore oil and gas traffic at the port.

Accelerated low water corrosion (ALWC) - the bacterial cancer attacking steel piled marine structures around the world -- was found in the existing quay at Killybegs and around $1.7M was spent on repairs. As well as a state-of-theart cathodic protection system, an imaginative engineering design was needed to prevent ALWC reccurring in the new structure, says Kirk McClure Morton director Dr Michael Shaw.

'We call it a combi-combi wall.

It is a combi sheet piled wall tied back to an anchor wall, with tubular steel king piles.

This is combined above mean low water springs level with precast concrete units which shroud the steel piles, with the gap between piles and units grouted, ' he explains.

Specialist drilling kit from Seacore was brought in to drive the 1,080mm diameter 30mm thick tubular king piles up to 28m long, each with welded clutches for the Larssen LX32 in between. The massive sections from Cleveland Steel were all shipped to site. The ground conditions were difficult, says O'Regan.

'It's silts overlying sands and gravels and very dense stiff to hard clay with numerous cobbles and boulders. We used an IHC280 hammer - the largest ever used in Ireland, to drive the piles to rock. Seacore cleaned them out and then drilled a hole slightly less than the diameter of the piles to socket them 5m into the rock, ' he says.

Extensive site investigation including 112 boreholes allowed the client a partial buyout of the Clause 12 unforeseen ground conditions risk in the Institution of Engineers of Ireland 3rd Edition standard form of contract.

An impressed current system has also been installed to provide cathodic protection to the steel piles (which have been painted) and the reinforcement.

'All the steelwork is connected to the impressed current system. The structure has a 50 year design life, but with proper maintenance it should well exceed that, ' says Dr Shaw.

Current fed through the system is connected to a monitoring terminal in the harbour master's office at the port. Voltage can be varied if necessary.

The vast reclaimed area accommodates a range of buildings, which also form a significant chunk of work under the $53M contract. Among the more spectacular structures are the harbour offices complete with 360infinity viewing tower, and a church-like boat repair building, which boasts a gargantuan 14m wide 22m high door, Europe's largest, says supplier Jewers.

The project is the largest ever investment by the Irish Department of the Marine in a fishery harbour centre and is funded under the 2000-2006 National Development Plan's Border, Midland & Western Regional Development Operational Programme which is part-funded by the European Regional Development Fund.

O'Regan says the job was won in the face of stiff international competition.

'We really wanted this job - it has everything from marine and civil to building work, and was food and drink to us, ' he says.

The new works, due to be completed in spring next year under the 112 week contract, will be a pristine new home port for the 'Boys of Killybegs', famed in song, as they come rolling home off the Atlantic wave.

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