Construction of a microtunnel with a length of 135 m and an internal diameter of 2 m, for the collection, drainage and storage of the exceptional first-flush rainwater from the railway underpass serving the station.
The work has several technical and operational characteristics: the launching shaft and the construction site were located adjacent to platform 1 of the Bologna Centrale station with very restricted areas available for carrying out the works, the microtunnel crossing the railway tracks and shield recovery were performed in an unconventional manner. Indeed, due to the operational difficulties relating to the construction of a recovery shaft at the railway tracks, I.CO.P. has proposed the pulling-back solution which involves the recovery of the drilling shield inside the r.c. pipe, with non-recoverable extension kit and shield.
This was possible by using a special drilling cutter, equipped with a double shield: the first internal shield (= AVN1500) has a diameter slightly smaller than the internal diameter of the r.c. pipe, while the second external shield (extension kit) has a diameter slightly larger than the external diameter of the r.c. pipe. At the end of drilling and after unhooking the cutter head, the first shield can slide inside the microtunnel and then be recovered from the launching shaft while the second shield, the outer one, remains in place.