Excavation of deep shafts using vsm technology

In the Dante-Garibaldi section of Line 1 of the Naples metro system all the ventilation chamber shafts have a finished diameter of 4.5 m (15 ft) and excavation depths of between 30 and 40 m (98 and 131 ft) and are, for almost all of their vertical length, immersed in groundwater. In addition, their location affects the traffic flows of the City’s arterial roads during the construction works. These conditions have necessitated the use of innovative operating techniques to allow performance of the works in accordance with the required safety standards for the operators, and as rapidly as possible to minimize their impact on road availability. The technology used for performance of these jobs is VSM (Vertical Shaft Sinking Machine) used for the first time in Italy for the excavation of small and medium-diameter shafts on Line 1 of the Naples metro system. This technique allows excavation in the presence of water and, with the installation of prefabricated lining rings, results in a finished job similar to a tunnel made with traditional boring machines. The machine, of German make, consists of a cutting tool mounted on a telescopic arm which allows the excavation to be shaped according to the required diameter. The whole system is connected to a ‘sinking machine’ which, using special mechanisms, controls the whole excavation system and lays precast concrete rings which, under the effect of gravity, follow the progress of the excavation. This operating methodology is fully mechanized, allowing smaller jobs to be performed in complete safety and extremely rapid timescales which certainly could not be achieved using traditional techniques.