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Italian job

BATTERED VESPAS, cars driven like gladiatorial chariots, and lumbering trolly buses have for decades been Naples' staple modes of transport.

But next month sees the opening of the latest 4.5km section of city's metro and work is already starting on the next 5km stretch. By 2011, if all goes according to plan, there will be 25.5km of metro 'linea uno', providing Neapolitans with a new public transport spine.

Site preparation and archaeological investigation is now going ahead from Dante through to Naples' rail terminus at Piazza Garibaldi.

Five new stations will be built and contractors, yet to be appointed by concessionaire Metropolitana di Napoli, will need to be extra vigilant.

The route passes through the heart of historic Naples.

Project engineer for client the Commune di Napoli, Antonio De Risi, is particularly anxious about the stability of buildings with shallow foundations, highly susceptible to movement in the predominantly pyroclastic material and made ground.

Structures could also suffer if the high water table along the alignment falls - the Dante-Garibaldi section will be up to 25m below this.

But original cut and cover designs were abandoned in favour of full face excavation to minimise disruption above the ground .

As with previous sections of the metro, construction will start with the station shafts. Diaphragm walls will be installed but ground anchors with temporary steel trusses will be used during top down construction.

Once these shafts are water-tight, the ground will be frozen to allow construction of stub tunnels.

Earth pressure balance machines will then be driven from these stubs - thought to be less risky than running TBMs straight through the diaphragm walls.

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