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Express success Italian engineers are rapidly completing sections of a high speed rail network that will link major cities the length of the country.

While the UK's Channel Tunnel Rail Link is in turmoil, across continental Europe engineers are busy building a high-speed rail network that will provide rapid travel for both passengers and freight throughout the region.

In Italy, the Trenno Alta Velocita is made up of six major city links, forming connections similar in concept to the German ICE system. The TAV joint venture is 45% owned by Italian state railway company FS and the rest is privately owned. TAV is the owner and operator for 50 years and is client for all six sections.

Construction of the latest section between Bologna and Florence has been going on for the last year or so, but although some 90% of this 78km route is in tunnel, tunnelling only started a few months ago. The L3,959bn (£1.4bn) project is due to finish at the end of 2002. A complex planning procedure between 1992 and 1995 drew together regional authorities, the government and local municipalities to secure the agreement of the various parties along the route.

The new line is expected to almost halve travel times between the two cities. TAV services will be the sole user, with freight and commuter trains running on existing lines.

The reason for the seemingly slow start to tunnelling is that Cavet (a consortium of contractor Impregilo, consultant Fiat Engineering, CMC Scarl, Itinera, Federici and CRCPL), working for main contractor Fiat, had to build some 100km of new roads to provide access to the route's remote tunnelling sites. These will be handed over to local authorities when the tunnel is finished. Some of the roads were actually used as a trade-off for permission to build the route as they will provide access to remote villages. Also eight residential areas had to be built at base camps along the route, housing up to 300 workers each.

Bologna to Florence is considered to be one of the most difficult sections of the TAV. It is made up of nine main tunnels totalling 67km, plus 11 access tunnels and two junction tunnels that will serve as links into existing lines in the cities at either end. Just over 1km of viaducts and 4km of embankments are included in the contract.

Even though work started in June 1996, some sections of the route are yet to be finalised. The details of the 18km long Vaglia tunnel link at the Florence end are still being hammered out. Work is progressing on a 6km stretch of the tunnel, but the consortium will have to negotiate an additional payment for the remaining 12km when the route is finalised.

The wide variety of rock types along the entire route has meant that Cavet has had to employ a variety of tunnelling techniques. Generally, ground treatment consists of grouting Sireg glass fibre reinforcement rods drilled into the tunnel face ahead of the drive, with steel fibre reinforced shotcreting over steel support arches. Elsewhere, methods include jet grouting umbrellas, fibreglass face support and rock bolting above, below and ahead of the face. In more difficult ground a small diameter pilot tunnel is driven first and a series of glass fibre ground supports installed in a radial pattern to support the ground for the main excavation. And near tunnel entrances, where the cover is small, permeation grouting will be used.

The ground can be extremely problematic. During construction of an access tunnel to the Raticosa tunnel, work was suspended after only 200m because of unexpected high rock convergence. And to stop the tunnel collapsing, it has been filled with concrete. In the last six months the contractor has been carrying out ground treatment of the mixed clay and boulders around the tunnel and is now carefully removing the concrete with probe tunnels. But Cavet project engineer Marco Pignorini does not expect the problems to affect the overall project programme, with lost time to be made up over the next few years.

At Vaglia ground conditions are better. Competent limestone with clay is being excavated with hydraulic hammers, with the addition of drill and blast where the rock is especially hard. Tunnellers are working around the clock, although not for seven days. But Cavet expects to start working non-stop some time this year, when more faces are open .

Around 6m per face is excavated every day, in 1m and 2m stages depending on the rock quality. The steel rib elements, which are 290mm wide and 160mm thick, are brought to the tunnel in four sections, bolted together and lifted into place at 1.20m centres. When one or two ribs are in place, shotcrete is sprayed on, followed by a geotextile and a PVC waterproofing layer. The final insitu concrete lining will be cast using 12m long Cifa travelling formers. The tunnel invert will be excavated at a later date. All the tunnels will have finished internal diameter of around 11m and will carry twin tracks.

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