Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to a newer version or another browser.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

Hidden agenda

Lairig Eilde bridge - The new Lairig Eilde bridge in Glencoe is a 'look from me' rather than a 'look at me' sort of bridge. Ruby Kitching went to Scotland to discover its charms.

For engineers working in the harsh climate of the Scottish Highlands, the men working on the Lairig Eilde bridge replacement project in Glencoe have uncommonly soft, clear, young looking skin.

Their secret- The daily, liberal appliance of Avon's Skin-so-soft moisturising cream. However it is not singled out as a defence against the high winds, torrential rain and cripplingly cold temperatures; they claim it is the best product on the market to keep the highland midges at bay during the summer - the high season for attacks.

The site is certainly chirpy regardless of the little 'blighters' flitting around. But then that could be because the engineers are working in one of the UK's most stunning landscapes. Lairig Eilde on the A82 from Glasgow to Fort William means 'pass of the hind' and takes its name from the stream which tumbles into the River Coe at that point creating a spectacular waterfall.

The bridge is a popular tourist stop-off.

'It's a wonderful place to work, ' grins Scottish Executive project manager Andrew Brodie.

The ú4M ($7.2M) Lairig Eilde project involves replacing a crumbling 1930s reinforced concrete road bridge with a wider carriageway and taking the opportunity to incorporate laybys, a footpath and waterfall viewing platform. Work started in April and engineers are now casting the first of two 1.5m diameter reinforced concrete piers. These are seated in 4.5m deep sockets in the river's rock embankments.

The existing structure had suffered years of corrosion from de-icing salts and is one of eight bridges which will be replaced along the A82 due to similar structural problems. All are monitored for movement every six months.

The project is being led by the north west Scotland highways maintenance consortium BEAR Scotland which includes consultant Jacobs Babtie, road building contractor Ennstone and maintenance contractor Ringway. Client for the scheme is the Scottish Executive and main contractor is Nuttall.

The deterioration of the bridge had reduced the concrete to powder in some parts. 'You wouldn't be able to get a bond with the concrete with carbon fibre or new concrete, ' says BEAR Scotland consultancy manager Brian Gordon.

The location's popularity with tourists, however, has meant that the road could not be closed to traffic during the bridge works. Before demolition could begin a temporary steel bridge was built alongside, with a separate pedestrian bridge to view the waterfall.

With affic diverted on to the temporary bridge in August demolition of the original started.

To keep disruption to a minimum, the process was more 'dismantling' than demolition.

Longitudinal beams and spanning deck sections were chipped away in turn before jacking off the crossbeams. A temporary platform below the structure collected stray debris.

Three original columns will be used as temporary props to support the formwork for the new bridge which is being constructed insitu. A grid of steel beams will be placed on the columns before timber formwork is fitted.

The 240m of carriageway improvements include widening the road from 5.9m to 7.2m and straightening it in plan to make it safer. This required blasting 3,000m 3 of rockface to gain the extra road width during nine road closures of 23 minutes each.

'We drilled a series of holes into the rock and then blasted in front of them to create a rough look, ' says Nuttall site agent David Anderson. Any evidence of boreholes was chipped away to create a more natural finish.

In other locations, road widening will be achieved by constructing cantilevered road sections using precast concrete.

Work will begin after the main Lairig Eilde section is complete in December this year.

The main site constraints arise from the fact that the A82 is the main road from Glasgow to the North West and can only be closed for short periods.

And since the road is already cut into a rocky outcrop, there is limited land available to house facilities, store materials or accommodate a tower crane.

Even the mobile plant being used takes up the whole width of the single carriageway when shifting rubble to the storage site.

It was this lack of space that dictated insitu construction.

Precast units could not be stored on site, nor was there swing room for cranes to lift units into place.

The 12.25m wide, 1.36m deep bridge deck is curved in plan and at gradient, explains Anderson, which will make casting deck sections challenging.

Stainless steel reinforcement and tying wire will be used in outer layers of reinforcement throughout the structure to ensure it lasts longer than its predecessor. Usually silane would be sprayed on the finished concrete surface to protect it from chloride attack.

But as the structure passes over a river and is in a site of special scientific interest, the spray particles could cause contamination during application. The bridge would also have to be closed to traffic and covered in sheeting for recoats every 20 years.

Using stainless steel added about ú200,000 ($349,000) to the cost of the bridge, admits Brodie - but is a cost worth paying to ensure the durability of the bridge over the 120 year design life.

Have your say

You must sign in to make a comment

Please remember that the submission of any material is governed by our Terms and Conditions and by submitting material you confirm your agreement to these Terms and Conditions. Please note comments made online may also be published in the print edition of New Civil Engineer. Links may be included in your comments but HTML is not permitted.