The widening of Italy’s Nazzano Tunnel on the A1 motorway between Milan and Naples finally got under way last month, after the original start date of March 2000 (T&TI, March 2000, p13) was postponed after the contractors pulled out.

Cossi Costruzioni recently won the second call for tenders on this world-wide first for tunnel widening, after Ferrovial & Agroman pulled out of the original contract.

The US$31M contract is for widening the 337m long tunnel from two lanes to three – 12.2m to 19.7m – without interrupting traffic flow.

The widening, which will take place above a shell which protects the traffic underneath, will follow four main stages. First, the creation of a fibre-reinforced shotcrete ‘shell’ along the extrados of the future cavity using mechanical precutting technology. Secondly, excavation of the ground in steps under the protection of the newly formed precut shell and demolition of the original lining. Thirdly the prefabricated segmental final lining is placed very close to the face according to the active arch principle. Thirdly and finally, the widened section of the tunnel has its invert constructed to complete the tunnel’s new diameter. The innovative process is scheduled to take about 12 months.