Projects: Underground engineering
Main features of 'I Berici' tunnel:
- Bidirectional bore
- Total length: 1866 meters
- Total wide: 8 meters
- Evacuation tunnel in case of fire (entryways every 150 meters)
Underground works for the Monti Berici underpass
The project entailed building an underpass under the city of Vicenza in order to relieve city road network congestion and to act as an artery which reorganizes the whole Vicenza area road network.
The system consisted of three different stretches:
- Main east-west artery (L = 4.0 km);
- Link road to the industrial area;
- Link road to the railway station and alteration of Mazzini boulevard.
The most characteristic structure in the project is the 'Berici' tunnel: it is a two-way single bore with 8.00 m wide roadbed (total length of 1866 m).
The most problematic aspect tackled when drawing up the design was the change in height in the tunnel, which had to take the following into account:
- The need to keep as much of the route over the ground-water table as possible in order to use excavation sections without inverts (cost reduction);
- The need to pass under the high speed line being designed;
- The need to pass under the River Retorto and River Bacchiglione, whose beds are about 7 m lower than the natural surface level;
- The need to implement longitudinal gradients which are not excessively steep in order to limit exhaust gases and minimize the flow rates of the ventilation systems required;
- The need to place the lay-bys outside the sections under the water table to keep building costs down.
Given the length of the tunnel, a design solution to evacuate users in the event of fire was proposed. It entailed building an underground passage between the road surface and the invert, with internal dimensions of 3.00 x 2.30 m, connected to the carriageway at special access points every 150 m. This proposal ensures that users may reach a safe smoke-free escape route on foot in the event of fire within a maximum distance of 75 m.