In a first for Italy, contractor Webuild is using increased air pressure to create a hyperbaric atmosphere in a section of tunnel it’s building under Naples for the Naples-Bari high-speed-high railway.
It means workers have to sit in a compression chamber for 20 minutes before they can go to the excavation site.
But the advantage is that the higher air pressure, created with compressed air, pushes groundwater out of the excavation area.
This reduces the risk of subsidence under a dense, urban area, because ground water isn’t being removed through the tunnel boring machine along with the captured soil and rock.
It also protects the aquifer by keeping it apart from cement mixtures and chemical additives from the tunnel lining during construction.
Webuild said a 650-metre section of the tunnel is being excavated non-stop now thanks to the technique.
Workers need training to work in the pressurised atmosphere, and acclimatisation in a compression chamber, which processes 20 workers per shift.
Depending on the excavation phase, the pressure fluctuates between about 0.3 and 1.2 atmospheres.
The tunnel is due to be finished in mid-2025.
The 145km Naples-Bari railway is scheduled for completion in 2028.
It will cut journey time between the two cities to two hours, down from four.
It will have nine tunnels, including the 27km Hirpinia Tunnel, 25 viaducts and 16 stations.
Webuild is working for Rete Ferroviaria Italiana.
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