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).