Minister of Transport Jozef Ráž (nom. Direction) mentioned last year that a boring machine known by the abbreviation TBM (Tunnel Boring Machine) could be used to dig the Carpathian highway tunnel near Bratislava.
This is exactly what the Polish construction company Budimex used when excavating two railway tunnels near the town of Nowy Sacz, located near the Slovak border.
A smaller evacuation tunnel with a length of 3.8 kilometers was dug by a modern machine in less than a year. “He cut an average of eleven meters and a maximum of 22.8 meters per day,” describes project director Marcin Curkowicz from Budimex.
In Slovakia, it is building the D1/D4 highway intersection near Bratislava and has also expressed interest in the construction of the Turany – Hubová section of the D1 highway.
In the interview you will learn:
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Why did the Poles decide on TBM tunneling technology,
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what problems did they have when stamping with water,
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why did you choose a machine from China,
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whether this machine could also be used for Slovak tunnels.
Why did you decide to dig the tunnel with a TBM machine and not the Austrian NATM method, which is based on blasting the rocks in parts?
The TBM method was already commissioned in the project of a larger train tunnel. For the side and smaller evacuation tunnel, the Austrian method was first considered. With it, a tunnel can be dug from both sides.
But with this method, we would not meet the construction deadlines. We also assumed that there would be problems with water and gas (methane) during excavation, so we also changed the technology to TBM for the evacuation tunnel.
What water problems did you expect?
According to the project, we assumed that the water pressure in the tunnel would be around four bars, but additional measurements showed that in some places it could reach from ten to twelve bars.
That would be a risk for the stamping machine. It was set to a water pressure of up to six bars, above this limit we would have to stop the machine because it could be flooded.
After all, there was no such problem with the water pressure. Rather, we had a problem with the lack of water in the rock, which we need during drilling for cooling and cleaning.
With one machine, we needed 1,500 cubic meters of water per day. We had to take it from nearby sources from the city of Nowy Sacz and Limanowa.
How many meters per day can a TBM machine excavate?
Estimates were around twelve meters per day, finally the smaller machine cut an average of eleven meters and a maximum of 22.8 meters per day. We were limited by the amount of cut rock to transport.
With faster drilling, we would not have time to transport the excavated rock. However, the larger machine reached a record daily maximum of 46 meters.
How did you take the cut rock out of the tunnel?
In a smaller tunnel, the material was transported on rails in wagons. An industrial train delivers the concrete fragments of the tunnel walls and takes back the excess rock and soil.
For the larger tunnel, we used a conveyor belt to transport the material. After drilling each meter of the railway tunnel, we had to remove approximately one hundred cubic meters of material.
To what extent does this technology reduce the risk of overcutting?
In the TBM method, the equipment simultaneously drills the tunnel, removes soil and installs concrete tunnel walls, so overburden is limited. If any overcuts occur, we can regulate them by adjusting the machine.
How is the safety of workers ensured during TBM punching?
It is relatively safe work because people are not in front of the machine, where there is a lot of pressure, but behind it.
For example, we have to employ divers who can change tools in the stamping equipment under high pressure. In addition, there are security rooms in the tunnel where employees can hide for 24 hours in case of an accident.
Will you also save on the number of people when stamping compared to the Austrian method?
