Open-cut tunnels

On commencement of activities during performance of the first lotes of Line 1, there was still no proven technology for the excavation of bentonite diaphragms: it was decided therefore to create the tunnel piers inside excavation shafts shored with spiles and wooden panels. The occurrence of bentonite diaphragms for which the first experiments had been carried out on Line 1 in Milan allowed much deeper excavation, especially on Line 2, even in the presence of water, and with greatly reduced working time. Now, with the greater difficulties resulting from the depths reached by the excavations, often with correspondingly said high water heads, or in the presence of large lithoid formations, even the usual clamshell diaphragm is overcome by the hydrofraise technology that provides greater verticality of the panels, improved hydraulic sealing of joints and a speed of execution which is incomparably superior: in projects on the lower section of the Naples Line 1, and on Line 6, extensive use has been made of this technology.