Currently to develop the A1 motorway in Italy, the busy part-section between Bologna and Florence (90,000 vehicles/day) is being augmented by an alternative route – the 2,413 m long Sparvo Tunnel with 2 parallel running bores each with 2 lanes and a hard shoulder. The geology in the tunnel route largely comprises clay, sand and limestone with mine gas present to a high extent in some sections.
While building the tunnel, the 4,500 t heavy, 130 m long EPB shield Martina (S-574; Herrenknecht AG) – with 15.615 m boring diameter the world’s biggest EPB shield – broke through the first bore after 12 months at the end of July 2012 attaining peak rates of 22 tunnel metres/day. In the process up to 4,215 m³ of earth was removed on a daily basis (altogether 458,451 m³ of excavated material), representing a major challenge for the site management. The soil containing gas required special safety precautions, such as ensuring that the conveyor belts were completely encased, permanent fresh air intake for all sectors as well as continuous monitoring to make sure the casing was tight and of the gas concentration. After breaking through the first tunnel bore the EPB shield was turned and drove the second tunnel bore at a gap of 20 m from the first one. The result was even more impressive: peak values of 24 m/d and 126 m/w were achieved. The second bore was broken through on July 29, 2013. Both tunnel bores were fitted with 2 m wide rings with 15 m diameter made of reinforced concrete segments (70 cm; 9+1), produced in a nearby plant.⇥G.B.