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On the grid in Valencia

The race is on to complete ground improvement work to allow a Spanish city to play host to next year's Grand Prix of Europe.

The city of Valencia on the east coast of Spain is no stranger to big races – it already hosts the prestigious America's Cup sailing event and the nearby Ricardo Tormo track is a regular car testing venue. But in August 2009 a new challenge rolls into town in the shape of Formula One's Grand Prix of Europe.

Site workers have already began to create a harbour-side street circuit and ground engineers are under pressure to reach the finishing line before the real race can begin.

The 5.47km racing grade track will include a section of new road running through an old industrial site that will link the circuit at its south west corner.

A river runs along a 1km stretch of the new section and the ground comprises alluvial material typical of the east of Valencia near to the sea. As the ground here is not strong enough to lay the road directly on top a joint venture between Pennine and Geocisa is using top-feed, wet vibro stone columns to improve the ground's bearing capacity.

The work is being done for client Generalitat Valenciana (the local government) by the main contractor (a joint venture between Fomento de Construcciones y Contratas, Pavasal and Becsa) and consultants Typsa and Ayesa.

"The approach to the job is, in a way, very simple," says Geocisa ground improvement manager Alejandro Segundo González. "We need to improve the characteristics of alluvial soil that lies beside the river for the new race track."

But González says the project is being complicated by the short project time allowed to get the site ready for the big race. "The client wants us to finish a project that we would expect to take four months in just two months. In addition, there are many others working, creating lots of site traffic and making our job that much more difficult."

The £700,000 contract involves installing a total 10,000 columns at depths between 6m and 12m (although more typically they are between 7m and 11m). The ground profile comprises about 2m of fill that overlies about 4m of consolidated clay and then between 6m and 7m of sands and gravels.

These columns are being installed by four rigs, each working 24 hours a day, seven days a week to complete the work in double-quick time. Pennine overseas contracts manager Jon Chevin agrees that working under these time constraints has been the biggest challenge on the project: "To meet the tight programme we have had to pull in two rigs from North Africa, one from the UK and one from the north of Spain, so it's been logistically complicated."
Each of the four sets of equipment comprise a Pennine manufactured HD 150 vibro flot mounted on a 70t or 80t Geocisa built telescopic crane, each with Landini jetting pumps. In addition, each set of equipment is instrumented with Pennine data loggers to check the stone column quality.

Operators vibrate the flot down to depth to create voids in the soil before retracting it to begin introducing stone that forms the 800mm diameter columns. An excavator then pushes this 20mm graded material to the top of the column location before the tool is vibrated down again. The flot advances and retreats repeatedly to force the stone down and compact it to form a column.

This process is aided by the use of water flush down the hollow inside of the flot, which helps to remove fines between the stone to create a tighter compaction.

Chevin says air flush is used more frequently by the firm for vibro stone columns but for the high capacity racing track, water is more effective at removing fines to create a more compact column. A feature that is particularly important in the weak alluvial material on site.
Although the 20m high cranes are doing their job well and helping to move the project quickly towards its deadline, the jibs are too tall to work the entire area. This is because in three different places, power lines stretch across the site and are too low to provide clearance for the cranes.

The main contractor decided to use band drains to improve the ground's soil bearing capacity in these areas, installing them to depths of about 4m. The stone columns are installed at 2m centres directly beneath the track and 2.4m centres elsewhere.
In addition to the difficulties manoeuvring around the site, work has to be carried out along the narrow stretch in a specific sequence dictated by the presence of an underground water pipe.

The pipe serves a nearby aquarium and runs underneath the north half of much of the length of the new road section.

The water supply cannot be interrupted so site workers are operating in the south part first and laying a new pipe beneath where the pavement will be.

"It makes it more difficult," says González. "We've already got a small area in which to work in one half of the site and we are not alone – in a 1km stretch there are maybe 15 activities going on at the same time. We would much prefer to have room to be able to work across the street."

But this option means that the new pipe will be completed and in place before the water supply is switched over from the old one. Work will then be able to continue improving the ground on the remaining half of the site.

On completing this work, the main contractor will follow on building the road that will have two lanes in each direction and two new roundabouts.

Following the Grand Prix of Europe in Valencia on 22 to 24 August the new road will be open to the public and will be another feature of the larger project to redevelop and regenerate the city's marina.

Work began on site on 22 October and each rig is working at a rate of installing 60 columns per 24-hour period. The tight deadline means all the stone columns have to be installed by the end of December. It is a race Pennine and Geocisa think they are on course to win.

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