ABOUT THE SAFETY OF METRO 4 CONSTRUCTION

For the time being we know about the exact causes of the collapse of the Cologne Archives building only as mush as published in the press. According to the news the tragedy occurred adjacent to a tunnel section, which was being built with a methodology somewhat different than that of Budapest. For metro 4 the experts use open construction method only for the building of station structures and train-turning facilities of end-stations, but these stations as well as other facilities are built with the most state-of-the-art methodology. In case of tunneling works it is the same. Tunneling method with a TBM is definitely amongst the safest ones. It is needed so, as the alignment of metro 4 runs almost all along under built up surface and old buildings.
With regard to the 10 stations for 9 locations the structure building works have already been completed with no problems, and also for the Baross Square site this process will end soon. Not long ago TBMs finished the Buda side tunnel building with almost no trouble. We are waiting only for the inside wall of the three layers to be also finished after the supporting structures at Gellért Square within a few weeks, and for the TBMs to be able to get into the station structure.

For a catastrophe similar to the one in Cologne not to happen in Budapest, the safety of buildings is being monitored in 24/7 with the help of an extremely sensitive computer monitoring system, which is capable of sensing even a hair's breadth of movement. Exactly for this reason it is very unlikely that a collapse alike to the one in Cologne would occur anywhere during the construction of metro 4. Also it is not a coincidence that the two TBMs are advancing with a relatively slow pace due to buildings on the surface, and in addition one is following the other with a space of nearly 100 m by this further reducing the minimal surface movements.

Effects evoked by the construction are monitored by so called Cyclops (automated geodesic instruments). These measurement devices can see 10 to 20 buildings at a time and continuously observe their movements. On each building subject to its size, 5 to 10 prisms are placed, and the automated monitoring system is sweeping these prisms with laser beam. For the metro construction now as much as 47 Cyclopes are monitoring 7,500 prisms, in several hundreds of buildings in the city. The computer controlled network measures in every two hours, and if the movement of a building nears the safety limit, it immediately notifies the experts in SMS message too, who can interfere in time. The system notifies for small movements as well. Such system monitors the buildings CH and K of the University of Technology, the houses of Thököly road and other concerned buildings too. If it was necessary, numerous such methodologies and options exists through which we would be able to interfere for the protection of buildings.

A good example for an effective action is the church building at Kálvin Square, which due to its deteriorated static condition would not have borne the surface movement anticipated. To reduce risks the engineers reinforced the foundations as well as walls and now the church stands on its “feet” more safely than before the metro station construction.

Alignment of the metro has to accommodate to all individual cases. Diameter of tunnels, thickness of their walls, and depth of the overall alignment were defined such way as they should mean maximum safety even for a surface in the worst possible condition. For metro 4 the alignment runs averagely at the depth of 16 to 32 m, but at Gellért Square it exceeds 34 m because of the age-worn surface and close proximity of the river Danube.


DBR Metro Project Directorate