Soil Improvement for Ventilation Adits at the Naples Subway Line 6-Video

Video Transcription

Video Summary

The presentation described ground improvement for ventilation adits on Naples Metro Line 6. Three sites had varying layers of sands, volcanic deposits, and Neapolitan Yellow Tuff, with excavation planned below the water table. At Santa Maria in Portico, staged cement- and silicate-based penetration grouting successfully created a low-permeability shell. At Victoria Square, jet grouting was used in loose soils, while Toretta Square was initially designed for combined jet and penetration grouting. However, jet grouting at Toretta caused substantial soil loss, forming underground chimneys and surface depressions and raising concerns about drilling-rig stability. Investigations linked the behavior to previously disturbed ground from earlier construction. Although jet grouting was considered technically feasible, the team selected ground freezing to reduce risk. A frozen soil shell was installed around the adit, and excavation was completed safely. The case illustrates that design solutions may need revision when unexpected ground behavior emerges during construction.

Keywords

ground improvement

ventilation adits

jet grouting

penetration grouting

ground freezing

Naples Metro Line 6