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Oban for business

TECHNICAL FEATURE: Dozens of Scottish lighthouses depend on a shore depot at Oban, which is undergoing a major modernisation. Alan Sparks reports from the Sound of Kerrera.

Since it was formed in 1786 the Northern Lighthouse Board (NLB) has been looking after the many lighthouses around Scotland's rugged coast.

Some, usually the most remote, were designed and built by the famous Stevenson family in the 19th Century. The Skerryvore light, 40km west of Iona, is generally regarded as one of the world's most graceful and dramatic.

Long since automated, the Skerryvore still depends on support from the NLB's shore depot at Oban. This is now being modernised and expanded to improve its working capacity and effectiveness for the provision of high reliability aids to maritime navigation.

The depot is used for berthing ships, landing and refuelling helicopters, building and repairing buoys and general maintenance work. Modernisation involves the construction of a new workshop, extension of the pier and hardstanding, along with access improvements and refurbishment of a listed building.

Gutting and re-roofing the old workshop building and inserting an extra floor will create new office space above a ground floor work area. This is in addition to the new build workshop, which will store equipment used by the NLB.

Mott MacDonald is responsible for managing the design specification contract through tender evaluation, contractor selection and project supervision. Design and build contractor for the project is RJ McLeod, with architect John Wilson Associates. Engineer Fairhurst is responsible for the land based work, while Wallace Stone & Partners is undertaking marine engineering works.

Work began in January this year, with official hand over of the site due on the first day of 2002. The original estimate for modernisation was £3.2M, but Mott MacDonald now expects the actual cost to be £700,000 less - and on schedule.

Most of the savings come from a change in the foundation details. The initial contract anticipated that most of the jetty extension would be built from marine piles. Geological surveys revealed that around 25% of the piles nearest the shore could be substituted with 7,500t of rock armour.

This design modification also allayed local residents' concerns over the possibility of noisy piling work. Most piling was driven through typical silt alluvium, which is both quieter and more workable than land based piling.

The 46, 508mm diameter 26m long steel tubular piles and six 760mm diameter anchor piles were vibropiled to reduce noise pollution.

'The most testing period of the project has been during the piling process, ' states RJ McLeod site manager Eric McGaskill, not without good reason. Although the initial specification proposed piling and land based works running in tandem, the logical construction method required all piling to be complete before other work could begin.

But the logistics were far from favourable.

Due to the narrow streets of Oban, the 26m long piles needed to be transported in two separate sections. The worst logistical headache, however, came from a particularly weak railway bridge, over which the 160t Manitou 777 crane, used for the marine piling works, was to be transported.

Even when broken down into lighter pieces the heaviest component weighed in at 148t. The answer was to use traffic lights to limit the bridge's load to only one lane at a time.

During construction the jetty continued to work, requiring a specific health and safety plan.

This needed to be practical and fully absorbed by each of the numerous subcontractors and NLB workers who would pass through the site. 'The project has been relatively plain sailing, ' claims Mott MacDonald project manager Alastair Walker, 'with good communication from all parties a key factor.'

The site stretches 100m along the seafront and retreats 60m inland. The steel portal frame workshop is to be 44m long, 20m wide and 12m high, supported on a reinforced concrete ring beam, built off steel 203 UC H-piles up to 14m long.

More than 100t of reinforcing steel and 2,000m 3of C40 concrete went into the 1250m 2,450mm deep new jetty insitu deck. Despite the relative isolation of the site, there was no skills shortage, with the only extra cost due to the use of a slightly more expensive local readymix supplier.

Western Scotland's notorious weather has been kind to the project so far and the 4.4m tidal range has been dealt with painlessly, avoiding any real delays to date.

RJ McLeod also commissioned a full environmental impact assessment due to the sensitivities of the region's nature and wildlife. Once groundwork began, it was found that the original, inadequate and undersized store, which was demolished as part of the project, had left behind a legacy of contaminated land. The only realistic option was to remove the 450t of contaminated material and send it to a specialist disposal site in Glasgow.

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