Metro line 4 - Milan - Italy

The M4 line of Milan underground (Blue line) is going to connect the town from east, end of line Linate Airport, to south-west, end of line San Cristoforo.

The protection against water in the stations of this new facility has been assigned, once again, to PVC waterproofing synthetic membranes manufactured by Flag Spa. Specifically, the system chosen to protect this critical line of public transport prescribed the use of waterproofing system Vacuum Flag.

The system designed by Flag Spa Soprema Group, in close collaboration with the engineers of Metropolitana Milanese, implies the use of two PVC waterproofing layers, Flagon BSL 2 mm. and Flagon BSL/ST 2 mm. That allow dividing the system into partitions.

The second layer is welded on the first waterproofing one, set on the weak-mix concrete and partitions previously smoothed with geotextile 500 g/sqm. to create sections of approximately 100 sqm. This second layer, Flagon BSL/ST, all over the lower surface has feet that enable to create a small gap between the two waterproofing layers. Exactly this gap is the core of Vacuum Flag System, because thanks to it and to the 3/4 pipettes used in each sector a pneumatic check is possible during the setting phases of the waterproofing system.

Far more important is the function performed by the pipettes during the whole life of the underground work, because if the section gets broken it will fill up with water. The water passing from the pipettes and the small tubes that bypass the main structure will set off the alarm flowing out from the connection boxes set in the station. The repairing is immediate and is performed injecting special water reactive resins into the small tubes.

Thanks to a jellification process the resin, after few minutes in contact with water, completely fills the section restoring the original waterproofing.