For six years, while Italian politics reeled under the impact of the corruption scandals of the mid-1990s, the tunnel boring machine deployed on the construction of Genoa's new metro system sat idle in the ground. Careful maintenance throughout the enforced stoppage ensured it was restarted in the spring of 1999 without any problems. But now tunnelling has been halted once again.
In September last year, just 250m into its 2.8km journey, the TBM hit a 15th century steel mooring buoy buried during one of successive land reclamation projects to provide deeper quayside berthing. Contractor Ansaldo replaced the damaged gears and manoeuvred the stricken machine to a ventilation shaft, from where it was dug out. Manufacturer Wirth is now repairing the TBM's damaged transmission at its workshops in Germany, while Ansaldo is busy stripping down and reconditioning the rest of the machine.
Ansaldo construction manager Tommaso Di Lallo is expecting to reassemble the TBM and start tunnelling again in October. But, he notes, the accident has cost Lira 1.5bn (US$700,000) and put tunnelling nearly 12 months behind schedule. 'The true cost of the delay is not clear yet.'
As main contractor, all risk on this Lira 270bn job lies with Ansaldo.
Income will be hurt badly if a claim against unforeseen ground conditions is not upheld.
Ansaldo, part of the Metrogenova consortium established to build and operate Genoa's metro system, is currently extending the network through the city's tightly packed harbour-front transport corridor. Hills rise steeply just a couple of hundred metres back from the water's edge, forcing roads and now the metro to compete for space.
A flyover was built four decades ago because the easiest way to go was up. But the metro has been forced underground - at its lowest point it is 17m below sea level - and is being constructed largely through a mix of centuries-old fill, clay and marl.
Genoa built the first phases of its metro system, linking Rivarolo to the north west with central rail station Principe, under two contracts in the 1980s and early 90s. Where the first phases of Genoa metro were single bore twin track tunnel, the new section is twin bore single track.
It is perhaps the most difficult section that is now under construction. This extends from Principe eastward around Genoa's historic harbour to a ventilation shaft at Pozzo Grazie and then Sarzano station at the start of an abandoned length of tunnel stretching to Brignole.
Metrogenova has just won a contract for the upgrade of the pre-war tunnel, abandoned in the 1960s. Ansaldo civil works supervisor Fulvio Nardi says work will involve extensive grouting to consolidate ground, minor realignment to accommodate the maximum 40m radius curves of the new metro rolling stock, and lining replacement.
Meanwhile, to compensate for time lost on tunnelling, Ansaldo is forging ahead with consolidation grouting along the length of the new tunnel. Civil works supervisor Fulvio Nardi calculates that 110,000 linear metres of grouting, consuming some 10.5M litres of grout has been completed. The construction programme of the new section's three stations has also been revised.
Problems with access to the TBM for the supply of precast concrete tunnel lining elements and removal of spoil dictated that no station construction could be carried out while drives are in progress. Ansaldo was originally plann ing to work f rom Pr in c ip e to Poz zo G ra - zie via Darsena and S.Giorgio stations and back again. Completion of Darsena and Principe stations would be left until last.
Under a new schedule currently being considered the TBM would be driven through to S.Giorgio and then returned to Principe for the second drive which unusually will run in the same direction.
On reaching Darsena the TBM would be hauled out, allowing the Principe and Darsena stations to be completed. The TBM would in the meantime be returned to a half-built S.Giorgio station for construction of the second bore to Darsena.
Spoil would be removed at S.Giorgio.
Nardi estimates that, providing Wirth gets the repaired TBM part back to site by September and no more obstacles are hit, 'we will be able to make up lost ground by February or March'.
Work in hand at Darsena and S.Giorgio is already having a bearing on future operation of the TBM. Subcontractors Rodio and Hydro have constructed the 800mm thick diaphragm walls of the station box and a series of barettes to provide temporary support to the station roof slab.
Excavation of the Darsena box is proceeding top down, with 35,000m 3ofspoil removed so far, while at S.Giorgio horizontal excavation via an access through the diaphragm wall is favoured - here 65,000m 3material has so far been disposed of. The TBM has been intended to arrive at the stations before work had progressed much beyond this relatively early stage. Distances between the diaphragm walls and the barettes had been calculated to give the TBM clearance.
But at Darsena and S.Giorgio casting of the concrete lining to the diaphragm walls is already well advanced. There is no way the TBM, which delivers tunnel with an unfinished diameter of 6.4m, will be able to pass between the finished wall and barettes on its first drive. The barettes will have to be demolished.
Meanwhile, the greater thickness of the finished wall will force realignment of the TBM through the stations. Instead of going though in a straight line, the track on which it runs will have to be diverted onto a path closer to the centre of the station.
Completion is due for 2002 and Nardi is confident the deadline can be met.
But, he notes, there are two absolute dates. 'Genoa is hosting the G8 Summit in 2001, and we have to get grouting completed by then'. Subcontractor SGF has injection rigs ranked along the road between S.Giorgio and Pozzo Grazie at the moment. Nardi is impressed by their rate of work, but thinks leaders of the world's most powerful nations might be underwhelmed by the spectacle.
'And in 2004 Genoa will be the European city of culture.' As a matter of personal pride, Nardi would like his home town to be a city of transport too.