Waterproofing tunnel rehabilitation with minimal clearance outline 

When the 117 year old Metro tunnel which connects the centrally located Omonia and Monastiraki stations, on the oldest line of the Greek capital’s metro network, required refurbishment, a range of BASF’s MEYCO Solutions were selected, notably the sprayable waterproofing membrane MASTERSEAL 345. Apart from a general reinforcement of the inner lining of the 650 meter long tunnel, the main task was to contain the continual water ingress in various parts of the tunnel and to waterproof the structure in its entirety. Furthermore, the project posed two additional challenges: On the one hand, there was an extremely tight time schedule to observe, and on the other, there was a limit of 15 centimeters for the overall layer thickness of reinforcement and waterproofing due to the rather limited inner dimensions of the tunnel  – trains must obviously still be able to pass through.

The basic reinforcement of the inner lining was carried out using sprayed concrete optimized with several admixtures: MEYCO MS 685 microsilica, GLENIUM 11 hyperplasticizer, Delvo®Crete stabilizers as well as the alkali free MEYCO SA 167 sprayed concrete accelerator were all used to ensure durable stability and to create the optimal substrate for the spray applied MASTERSEAL 345 waterproofing membrane. In places where repairs were necessary, this was done using the shrinkage compensated, thixotrope Emaco S88C repair mortar.

The secure sealing of leaking areas inside the tunnel, a constant source of water ingress, was another important step during the refurbishment work and a vital prerequisite for the smooth operation of the new electric engines of the metro trains. For this, the polyurethane based MEYCO MP 355 1K injection foam was used.

The tunnel surface was waterproofed using the innovative MASTERSEAL 345 waterproofing membrane, applied directly onto the sprayed concrete substrate. To facilitate speedy and precise application, a MEYCO Potenza Logica mobile spraying unit was employed, ensuring a consistent layer thickness of three millimeters thanks to computer controlled surface scanning. The successful application of the waterproofing membrane was then followed by a finishing layer of sprayed concrete with Masterfiber 12 polypropylene fibers for effective reinforcement.