ABSTRACT
The paper deals with the application of grouting technology to improve soft rocks for tunnelling at Duomo station, within Naples subway Line 1 extension project. Located downtown in a deeply urbanized area, the station is composed of one access shaft, four platform tunnels and four inclined pedestrian access tunnels. The soil improvement was setup to allow boring the 8 station tunnels under a hydrostatic head of up to 30 m. An annular low permeability thick shell all around the tunnels to be excavated was achieved by penetration grouting. The treatment, entirely carried out from the already in place TBM tunnel, was fan-shaped. The tuff cracks were sealed by using at first high penetrability cement based grouts (fine and microfine cement) and then a silica-based chemical grout, through MPSP grouting pipes. In addition, one tunnel out of 8 was bored and constructed combining two soil improvement methods: grouting and artificial ground freezing.
