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Moving ahead

Transport stands out as the sector with the greatest potential for Scottish civil engineering, with diverse projects under way.

An extraordinary mix of recycled and low energy materials is proving its worth in an experimental road near Edinburgh. Waste products ranging from slag to spent oil shale have gone into the pavement which - six months after being laid - is performing significantly better than expected.

The Echline project is being carried out at South Queensferry to see what can be achieved with recycled and secondary materials, in terms of minimising overall energy consumption and virgin aggregate use.

Virtually the only virgin materials that have been used are bitumen and cement, along with a small proportion of new stone.

A breakdown of the Echline road's structure goes like this, from the bottom up: subgrade - stabilised insitu with PFA and cement; sub-base - spent oil shale aggregates bound with PFA and cement; road base - cold lay slag bound material made up of recycled aggregates bound with granulated blast furnace slag and PFA, activated with gypsum and lime; base course - hot mix asphalt incorporating recycled asphalt planings and foundry sand; wearing course - cold lay bitumen emulsion asphalt including (coarse) steel slag, (fine) blast furnace slag and very high performing polymer modified emulsion binder, supplied by bitumen specialist Nynas UK.

Currently untrafficked, the road has a single carriageway and is 100m long by 6m wide.

It was built between November 1999 and April this year.

Testing has taken place at one, three and six months following completion, and final tests will take place next April. The regime so far has included falling weight deflectometer testing and extraction of cores, down to 700mm to examine in particular strength and stiffness of the various layers.

'It seems that the pavement has achieved the expected performance and is still improving. The results are actually above laboratory expectations, ' says Nizar Ghazireh, senior research technologist of Echline contractor/promoter Tarmac.

Design requirements were for a trunk road-typical 100msa (million standard axles) and 40 year lifespan.

'We have used up to 85% of recycled and secondary materials and the savings are phenomenal, ' Ghazireh claimed.

The Echline design, if employed on a kilometre of dual carriageway, would take about 5000t of virgin aggregate compared with 45,000t on a standard design, he says.

The Echline project is the brainchild of the Scottish Executive Development Department which invited a number of contractors to bid to partner in the construction of a sustainable pavement. Tarmac was the preferred bidder.

'Echline is a very successful project, ' claims SEDD trunk roads division senior engineer Forbes Macgregor. 'It is raising awareness of what can be achieved with secondary materials and points to the potential for innovation when specifications are less proscriptive.'

Dredging operations to remove 80,000t of mercury-contaminated silt from the Union canal are halfway towards releasing a major source of revenue for British Waterways. Completion of the clean up in summer 2001 will also move the Millennium Link project a step closer to realisation of uninterrupted navigation along the Union and Forth & Clyde canals.

Up to 12,000 ppm of mercury were found in a 9km stretch of the Union Canal between Falkirk and Edinburgh by a 1992 British Waterways sediment survey of the canal network. The accepted safe level has been set by the Interdepartmental Committee for Redevelopment of Contaminated Land at 20ppm.

Removing the contamination means that industry can abstract water from the canal, paying British Waterways for the privilege and reducing its use of treated potable water. The funds raised by the canal operator can then be Land & Water Services is dredging contaminated silt from the canal bed using barge mounted excavators under a £3.1M contract with British Waterways. The material is being screened and treated with lime to dry the material and make it manageable for transportation to a purpose built engineering cell designed by Shanks Waste Solutions at the nearby Avondale landfill site.

'We are removing all vegetation and silt from the canal bed to a scorched earth policy, ' says Lassiere. 'The seed bed is being recreated to enable the vegetation to recover by depositing noncontaminated dredgings from other parts of the canal.'

Temporary track to create a major diversion for train services has been installed for the first time on the UK's rail network. Contractor Skanska pioneered the technique during maintenance work for Railtrack on the East Coast Main Line near Wallyford in East Lothian.

Skanska built the 400m diversion and associated signalling, overhead power and telecoms infrastructure between January and the end of April this year. During the Easter weekend, the contractor connected the new section of track and diverted trains during a 54 hour possession.

Skanska could then start the next phase of its £5M contract with Railtrack - stabilisation of 200m of trackbed subsidence.'This section of track has suffered continuous subsidence due to the collapse of disused coal workings which pass directly below, ' says Skanska project manager Gary Wilde.

'Railtrack Scotland imposed stringent speed restrictions on trains in February 1999 and needed to get service back to normal as soon as possible.'

Procurement for the design and build contract was carried out by interview and Skanska began work on the project almost immediately after it was awarded the contract in October last year.

'The Wallyford scheme has been achieved in less than half the time it would have taken under conventional tendering arrangements, ' says Wilde. 'We progressed from feasibility, design and approval right through to construction and reinstatement in just 12 months.'

Stabilisation work involved installing 330 minipiles of 200mm diameter to depths of between 10m and 28m into rock below the worked coal seam. Ballast and track was reinstated on a 300m long, 8m wide and 600mm deep reinforced concrete raft spanning the piles. The new track and related infrastructure was reconnected to the ECML during two 13 hour weekend track possessions in last month.

'Removal of the temporary diversion track is currently under way and we expect restoration of the area to be completed by the end of this year, ' says Wilde.

Major repairs to mainland Scotland's most northerly civilian runway at Wick airport took place this year under a special fixed price contract developed by the Scottish Executive. Own Period Tendering allows contractors to specify more clearly how long they think a job will take and price the work more effectively.

Consultant Scott Wilson was commissioned by client Highways & Islands Airport to design the most effective way of rehabilitating the runway surfacing. Scott Wilson director Simon Hindshaw says: 'Contractors are usually in a better position to give a good estimation of the time needed to complete the work and Own Period Tendering protects the client because if the work is finished early the contractor is paid accordingly with the amount of time spent on site.'

The surfacing to Wick airport's asphalt runways was last renewed in the early 1990s but potholes were exposing asphalt base layers, presenting hazards to aircraft.

Scott Wilson Pavement Engineering tested for residual strength using a falling weight deflectometer. 'We selected a 100mm grooved asphalt overlay, ' says Hindshaw.

'However, we had to search hard to find a local quarry that supplied an aggregate with the required polished stone value of 55.'

Renewal began in June with contractor White Mountain working at night between the hours of 19.30 and 07.00. The job was completed in September.

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