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Unblo c king Belfast

ROADS AND BRIDGES - Ulster is nally starting to see infrastructure investment. Alasdair Reisner went to visit the city's £104 million road decongestion scheme

IN 1983 the Westlink was something for Belfast to be proud of.

Over four years the road scheme - linking the M1 and M2 motorways through the heart of the city - had been a triumph of civil engineering. Despite the political troubles that were raging around it, the scheme had powered its way through and opened, at a cost of £23 million, in March that year, ready to carry up to 35,000 vehicles a day.

But in 2006 the Westlink is less popular. It has become a byword for congestion as it gets clogged up with a daily snarl of 65,000 users, each of which has had to get used to a slow crawl.

'One of the things you realise following the peace process is that infrastructure spending wasn't available during the Troubles.

We are now getting a bit of normality, ' says Leo Martin.

Mr Martin is project director for the Highways Management Consortium. In February this year the consortium, made up of local firms Graham and Northstone and European goliath Bilfinger Berger, was awarded a £104 million deal to declog the Westlink and neighbouring M1 motorway, along with a package of other work on the M2.

The design, build, finance and operate deal will also see the team taking responsibility for maintenance of 60 km of motorway for a 30-year period. It is said to be the biggest civil engineering task ever attempted in Northern Ireland.

So is this a case of the big European cont ractor weighing in with a bid and then hauling in a couple of local outfits to do the work? Not quite, according to Mr Martin.

'It was the other way round. Graham and Farrans had worked together previously on large projects in Belfast such as the Cross-Harbour Links in 1994, where, as the two biggest players, they got together to take out the competition, ' he says.

But with a job this size and given its financial requirements, they were looking for a large player to share the investment.

Bilfinger Berger brings more to the job than deep pockets.

The project involves significant work on underpasses at Grosvenor and Broadway - in essence, the kind of tunnelling work that the German giant has made its forte.

The first of these underpasses is at Grosvenor Road, where an existing junction is one of the main bottlenecks of the Westlink.

Here traffic lights cause stop-start traffic.

Work is currently under way to create a 200 m-long secant wall box using 1,200 mm, 25 m-deep bored piles along the line of the Westlink through the junction. Once complete, existing traffic will pass along the sides of the box while cross-traffic from the Grosvenor Road will be diverted onto a specially-built temporary Bailey bridge above the site. This will allow the team to go in and build a permanent bridge for the Grosvenor Road traffic on top of the secant wall.

Using top-down techniques, the team will then excavate a secant box to create the underpass for the Westlink traffic.

A similar top down approach is also under way at Broadway, where an existing roundabout currently means that each morning six streams of traffic, including vehicles coming off the M1, all converge on the same spot.

But this junction presents a second problem that frustrated commuters sitting in gridlock will be unaware of.

'At Broadway you have two rivers that need to be diver ted; the Clowney and the Blackstock. They combine right in the middle of the junction, ' says Mr Martin.

With their existing culverts, the rivers run through the middle of where the new underpass is to be built, so the team had to first figure out how to divert the rivers. There had been talk of burrowing it even further down below the road or even putting it in a hanging span.

But instead the HMC team is now working to install huge sect ions of prefabr icated concrete culvert that will lead the rivers to either side of the junct ion before both meet in a twin culvert to drain away on the other side. For the Clowney this will involve a 200 m diversion around the southern end of the underpass.

With all this water around it is unsurprising that the team wants to ensure that the Broadway underpass is waterproof.

While only the primary piles on the secant wall at Grosvenor are full length, at Broadway both the structural and secondary piles are going to full depth to create a watertight box. With the piles in, the team can again direct the traffic onto slip roads constructed outside the box.

The team will dig down about 1 m to create a base for the underpass roof slab. The new junction for non-motorway traffic can then be built on top. Finally the underpass can be excavated out to create a clear route for the motorway to flow underneath.

The third major section of junction reconstruction is at Stockman's Lane on the M1, which centres on a nine-span junction built in the 1970s. Already heavy loads crossing the junction have to do so at night, with police holding back other traffic because of fears the viaduct will not be able to take loads.

Now, with the need for the widening of the M1, an opportunity has arisen not only to replace the viaduct but to improve its appearance.

'You've got two bridges here, a northbound and a southbound with a gap between them. We were able to modify the existing southbound bridge to take four lanes of traffic - two in each direction, ' says Mr Martin.

This allowed for demolition of the northbound bridge and a more elegant replacement. Traffic could then be redirected onto the new bridge while the southbound viaduct is replaced.

'It is going to be more aesthet ically pleasing in that it will be two five-span bridges with no crossheads permitted.

'The central area of the junction below the viaducts was previously where antisocial behaviour was common, so it is being landscaped, ' says Mr Martin.

Overall the scheme will take three years to complete, returning the Westlink to its position as a source of pride for Belfast's civil engineers.