Suburban Railway

Location
Milan
Country
Italy
Year
1993 – 1995
Client
Impresa Quadrio Curzio S.p.A
Area
Infrastructures
Services offered
Geotechnical Engineering, Structural Engineering

Project description

Milan Suburban Railway is an almost entirely underground infrastructure crossing the city from North-East to South-East. It integrates the Italian State Railways, Ferrovie Nord Milano and the urban public transport networks, in particular with the three Milan Undergroud lines. CEAS designed about 200 m of blind hole tunnel in the urban area, between the stops of Repubblica and Garibaldi. In this section the two lines got closer gradually separating and the tunnel sections included a first double track part with about 10 m of net section, followed by a second double track part with 13.74 m span. The last part included two single track tunnels with 6.02 m span. The consolidation and excavation project included in the tender project had to be basically reviewed due to a great rising of the water table level during the first work steps. It involved a low water table head that could be coped with through reinforcement and waterproofing injections from pilot hole. Therefore, the excavations were made below the water table head more than 6 m from the excavation bottom level. This required reinforcement and a preliminary lining specially designed to supply the necessary watertightness and resistance to buoyancy.

The numbers

200 m of tunnel

6 m of water head during the excavations

13.74 m span in the double track part

ACTIVITIES CARRIED OUT

Structural executive design.
Geotechnical executive design.
Assistance to works management.

IMPORTANT ASPECTS OF THE PROJECT

Due to the changed hydrogeological conditions, the reinforcement injections for the cover were performed from the ground level, since the pilot hole, made some years before, was below the water table. The primary excavation bottom level was raised, to keep it higher than the groundwater level. Then the reinforcement and waterproofing injections were made from this primary excavation bottom level on the vertical masonry structure side and in inverted arch. Some metal centreing even in inverted arch was used in the part with a greater span and a higher head.
The project was repeatedly updated during the works according to the results of the water table monitoring. It was also systematically assisted by the development of finite numerical models in a non-linear field, thanks to the software developed by CEAS itself.