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Learning on the road

Highways Poland

An unusual concrete arch bridge is part of road upgrading for southern Poland. Report and pictures by Adrian Greeman.

Head south from the famous medieval city of Krakow in Poland, and you enter a region of small farms, rivers, and hill walks. Lovely for tourism, it is woefully inadequate for commerce, with narrow, rutted roads.

Accession to the European Union in 2004 has unleashed new developments and provided access to European funds.

One project already under way is using European Investment Bank money to create a new link across the Slovakian border.

Although just 30km long, the job is relatively complex, says Simon Hindshaw of supervising consultant Scott Wilson. It involves constructing a new alignment to replace an existing weight-restricted single carriageway road, bypassing village traffic jams and difficult gradients in 1km high Carpathian hills.

The new road will be a mix of dual and single carriageway which will be fully dualled later.

'A first border section with three-lane dual carriageway has been completed, ' says John Balfe, chief resident engineer for Scott Wilson. Now the main attention is on a 3km job close to the brewing town of Zywiec.

The contract - with the Polish arm of Skanska - contains two major bridges. The first of these curves across a small steep valley containing a live, if slow moving, earthslip. The second is an unusual three arch structure across a larger valley.

To pass the slip, whose presence is clear from the deteriorated condition of the existing road over the top of valley, a 247m long concrete box girder bridge has been built, using balanced cantilever construction for its central three spans.

'That eliminated the need for masses of falsework support in the steep valley, ' says Balfe.

'If there were any complexities they were in the curve and super elevations of the bridge, ' says Hindshaw. 'There are a 300m radius curve and a 7% superelevation to accommodate.' This bridge is now largely completed, allowing attention to shift to the second, 662m long, bridge with its elegant three arch support in the centre.

Arches are each 104m span.

For this job Skanska pressed for a major redesign. The original Polish design was also planned in concrete, but Skanska devised a precast system for the arch formation. It also substantially changed the side spans, from simpler insitu 24m long threebeam T sections to much larger 41m span two-beam Ts. This allowed it to modify and use a large travelling formwork gantry it already owned.

The 'Red Dragon', as the Polish workforce has christened it, was designed with German formwork maker Peri. Its 52m length supports a series of hinged shutters which come together to form the double T-beam shape of the 12m wide deck and two 'anges beneath. A 20m long nose moves the selfpropelling gantry onto temporary steel supports on the next pier.

Erection of the three central arches uses an unusual precast system. Skanska project manager Mariusz Swie ciak explains that each arch is actually a double structure with two parallel concrete arches separated by a central gap.

Cross pieces at intervals tie the two together.

During construction each arch is itself formed as a double arch, using two curved beams built up from precast elements.

The 1.4m deep units are up to 14m long and therefore a reasonable weight - 'some up to 25t' says Balfe - and need 'rm support as they are positioned by crane. Skanska is using 've hefty tubular steel temporary towers for each arch which require their own piled support in the soft ground. Four 600mm CFA piles support each one.

The complex shapes of the arch sections are cast close to the site and require some care.

Skanska altered the original semi-circular arch into a more 'attened curve, which means changing geometry on each element; the third arch which carries the bridge deck on a curve has gradient and superelevation changes.

Once the 600mm wide units are assembled to form the arch shape on the steel towers, the 1.8m gap between them is stitched with concrete making a total 3m wide slender arch, one each side under the road's post tensioned double T shape.

For Skanska the work has been challenging says Swie ' ciak.

The site is awkwardly placed in the valley and access is fairly dif'cult, not least because of scattered housing nearby.

There is little lay-down room for equipment and materials, he adds.

The remoteness of the area also made recruitment of staff and skilled workers dif'cult.

'And you need workers with experience to climb on these high forms and falsework structures, ' he says.

A wet summer brought problems with heavy mud and sticky clay, and winter is colder 1,000m up, with snow certain.

Despite the problems Swie ' ciak is not unhappy with progress, believing that around half way through the job he is approximately on schedule.

Meanwhile there is more to do on the other road sections with substantial earthmoving and shaping. Ground conditions mean this is not always so simple; the Carpathian region has significant faulting and transitions between folded areas of slates, sandstones, clays, shale and limestone, and frequent design detail changes are needed as embankments are excavated.

It will keep Balfe busy for another year, along with his 40-strong team. Most are drawn from local engineering 'rms and seconded to Scott Wilson for the duration of the project.

'The affing is vital, ' says Balfe. 'Although the job is done according to international FIDIC standards there are also complex Polish regulations to follow.' Polish law requires that engineers are qualified to sign off work in particular specialities, such as bridge works, and that they are responsible for signed off projects. 'It is quite a serious legal burden' says Balfe.

This may be the last such contract for Scott Wilson, or indeed any UK based consultant, says Balfe. Polish firms are becoming more experienced in FIDIC requirements and if, as client the General Directorate for National Road & Motorways hopes, there is money for further work, it may well be a purely Polish job.

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