Motorists travelling through the Pyrenées on the A7 autoroute between France and Spain cannot fail to have noticed the string of construction sites that has sprung up along the road south of the border.
Viaduct piers have sprouted and a vast work site has opened up at the foot of the mountains.
All are signs that the E1.1bn ($1.4bn) high speed line connecting the two countries is now well under way.
When complete, the 44.5km line between Perpignan in France and Figueras in Spain will connect the high speed rail networks of both countries for the first time.
It will also carry long distance freight through the Pyrenees, easing congestion on the A7.
The project is being const ructed under a 50 year design, build, finance and operate concession, the first European cross-border project of this kind since the Channel Tunnel (see box). Concession company TP Ferro acts as client, while its shareholders Eiffage of France and Dragages parent ACS of Spain are carrying out most of the construction work.
Viaducts north and south of the border are the most visible signs of progress, but the most technically challenging work is taking take place underground, deep beneath the Pyrenées.
Here, two tunnel boring machines (TBMs) have just begun construction of an 8.3km twinbore, cross-border tunnel.
Success of the tunnelling operation is critical to efforts to get the line finished by 2009.
Work on the $373M, 8.5m internal diameter bores started in July, after contractors had spent almost a year procuring two Herrenknecht TBMs.
The tunnel contractor is AEIE Tunnel de Perthus, a joint venture between Eiffage, SAS and Dragados. It is anticipating some tough ground conditions as work on the tunnel progresses.
Preparations have begun to treat an area of especially unstable schists and faulted granite ahead of the tunnelling work by injecting grout incorporating an accelerator.
With this in mind, excavation has started on a 1.1m long 40m 2 cross-section 'treatment gallery' near the tunnel's mid point, and between the lines of the running tunnels.
'We are treating this section because the ground here is very difficult, ' says AEIE tunnel engineer Jacky Segnana. The gallery is being created using drill and blast methods, and is accessed by an adit cut into the mountain side above.
'If we don't carry out grouting, we could have trouble with the TBM, ' says Segnana. TP Ferro chief executive Eusebio Corrigal adds that if the TBMs run into difficulties in this section, contractors can use the gallery to dig ahead of them.
Even though only 1km of the tunnel is in Spain, both tunnelling machines are working north from the Spanish end. Corrigal says that this is because Spanish land acquisition procedures are quicker than those in France, so it was easier to create the launch site and service area.
Outside the tunnel, contractors are working flat out on viaducts on both sides of the Pyrenées.
The challenges are different in each country and different construction methods apply as a result.
In France, the biggest viaducts are across a motorway, a trunk road, a railway and a river.
For speed of construction, it was decided to prefabricate these bridges in steel and push them out. This was especially important for the road and rail crossings, where limited time windows were available.
Road crossings include the skewed 267m crossing of the A9 autoroute. The deck is now being assembled next to the motorway, ready to be pushed out, while foundations contractors carry out piling work for one of the piers in the motorway's central reservation.
To the south, another 144m steel viaduct is being welded together before it is pushed out across the RN9 trunk road and a railway line. 'It will take one night in the second week of December, ' says Eiffage site engineer Nicolas Durame.
In Spain, the favoured viaduct material is concrete. There, crossings span steep sided valleys in the southern Pyrenées.
Contractor Dragados is also building two cut and cover tunnels: one 180m long and one 189m long.