Road tunnel along Wislostrada in Warsaw and a building failure on the construction site of the second metro line in Warsaw – the analysis of the possibility of removing parts of the tunnel’s diaphragm walls in order to build the “Centrum Nauki Kopernik” metro station.

In the beginning of 2013 we were asked by the general contractor on the second metro line in Warsaw, the AGP consortium, for urgent assistance in solving the problem of ensuring the stability of a road tunnel and how to build a new metro station. The foundation of the tunnel is based on three lines of piles/diaphragm walls, which are so long that they intersect with the new metro tunnel and thus needed to be shortened.

What made matters worse was a building failure that had occurred a few months earlier, causing a massive ground slide from below the road tunnel into the newly excavated pit for the metro station.

All earth works connected to metro drilling, pressure ground injections, excavating for the metro station caused the road tunnel to move upwards and downwards with the amplitude of 70mm! Based on geodesic measurements, site inspection and analysis of the design of the tunnel and metro station, we managed to assess the condition of the tunnel and recommended steps that had to be taken by the contractor in order not to worsen the situation and avoid further damage to the tunnel’s structure.

Interesting facts

The cavern that appeared under the tunnel after the building failure was 50m long, 25m wide and 8m high!! It was subsequently filled with concrete.

The acceptable differences in settlements between tunnel s supports during the works could not be greater than 30mm. Such a strict condition was given to ensure the safety of the tunnel, to avoid cracks or even losing the capacity

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