The Line 4 is a new underground line under construction in Milan, part of the city metro system and it will be the second driverless line in the city of Milan The line will be 15 km long with 21 stations.

Alpina is in charge of designing preliminary and detailed design of the structural and geotechnical works for 8 underground stations, 3 inter-stretch building structures, 3 tunnels, 1 bridge and n the design assistance on site during construction.

The works were engineered in loose soils below the water table, alongside the existing buildings or infrastructures in the city centre. The underground main structures are built using bottom-up procedures below water table or using combined bottom-up and top down techniques for high excavation depths (up to 30 m, 20 m below the water table).

Alpina carried out the final design of the structural and geotechnical works of five stations of the Milan Metro Line 5, as well as the tunnels of the Garibaldi junction. In particular engineering designs were provided for the Isola, Garibaldi, Monumentale, Cenisio and Tre Torri stations, all of the underground works of the Isola and Monumental stations for a total of about 1,8 km of tunnels in the urban area, in loose soil below the water table, alongside buildings or existing infrastructures such as the 70 m high tower at the AC Hotel.

As part of the project for the new Lyon – Turin high speed railway, this contract concerns the construction of the Avrieux shafts, a part of the safety site, a section of the base tunnel towards La Praz and the tunneling machinery chambers of the future section 05.

The main works concerning the shafts are broken down into two parts:

• Part 1 – Avrieux Shafts (n. 4 ventilation shafts);
• Part 2 – Tunnels at the bottom of shafts (connecting gallery, room at the bottom, ventilation tunnel, heads of the smoke shafts, smoke shaft at the intertube gallery). The basic solution involves the construction of four shafts of 4,26 m internal diameter and 5,20 m excavation diameter dug at Raise Boring aligned in pairs on two rows spaced by 2 diameters.
• The 4 shafts have a depth of about 500 m each, from the platform of Avrieux to reach the room at the bottom of the wells.
• The room at the bottom of the shaft is connected to the ventilation tunnel.
• The inter-distance of the shafts is 12,5 m with the exception of the two shafts at the entrance of the ventilation tunnel, which are arranged at 20 m distance to ensure the maneuvering area of the machines.
• The installation of the shafts must be compatible with the size of the opening of the ventilation plant at surface in order to directly open the 4 shafts in the future central platform. The constraint to be met includes the requirement to enclose the shafts in a rectangular area with footprint 28,0 mx 18,39 m.
• The excavation section of each of the four shafts is 21,24 m².

The construction method chosen consists of 4 main phases which are as follows:

1. Dig a pilot hole from top to bottom in about 15 inches (RVDS directional drilling).
2. Bore up to 5,20 m in diameter with the Raise-Boring method.
3. Install a temporary support from top to bottom once the bore is finished.
4. Final coating of the shaft from the bottom to the top with slippery or creeping formwork.

A jet-grouting soil consolidation treatment is necessary before RBM digging to ensure shafts wall stability.

The cuttings produced by boreholes fall at the base of the shaft in each sector of the basic chamber, divided into independent sectors by temporary partitions.

The construction of the concrete final lining is done by sliding or creeping formwork, from the bottom to the top. The presence of a seal between the coating and the solid structure significantly reduces the transmission of the weight of the coating to the rocks by friction. For this reason, in order to provide support to the coating, which would otherwise be suspended to the top of the shaft, 12 precast concrete hemispherical supports every 10m are anchored to the solid structure by HA32 bolts, 2 m long, inclined by 20°. The execution of the shafts is done in a soundproof acoustic shed able to limit the noise nuisances within the limits set in the NRE.

The Lyon–Turin Base Tunnel is a key element of the trans-European Network for passengers and freight, the West-Eastlink of Corridor V, connecting Lisbon to Kiev.

The twin tube 57 km Base Tunnel will be excavated through 4 access tunnels. Three different access adits are conceived on the French side: Saint-Martin La Porte, La Praz and Modane, and one on the Italian side: La Maddalena.

The excavation of the base tunnel has started with the 8 km section from Saint-Martin La Porte to La Praz.

Alpina carried out the Supervision of works of the access tunnel in Saint-Martin La Porte (in JV with Egis and Antea) and currently is carrying out the Supervision of works of the first 8 km section of the base tunnel (in JV with Egis).