The construction method: We build minimally invasively with the tunnel excavator

Introducing: our ‘Debohra’ tunnel excavator

Our Debohra tunnel excavator started work at the end of September 2024. It is digging its way from Matzleinsdorfer Platz along a route of around four kilometres to Augustinplatz in the seventh district and constructing the new line tunnels for the U2 underground line. This work is being carried out underground - similar to an operational ‘buttonhole method’. 

At the beginning of November, Debohra reached its first milestone: the breakthrough to the track switching facility and the Reinprechtsdorfer Straße emergency exit. In its first stage, it has built 240 metres of U2 tunnel.

All of the earth that Debohra excavates is transported away via a central shaft at Matzleinsdorfer Platz. This avoids dust and noise and a whole 20,000 lorry journeys through the city - which in turn saves up to 75 tonnes of harmful CO₂.

Tunnelling with the tunnel excavator

This construction method can be used for longer sections with a uniform tunnel course, whereby the ground must also be relatively uniform. The 50 metre long tunnel boring machine completes all work steps in one: digging the tunnel, sealing and lining the tunnel tube and removing the demolition material.

Open construction method ("lid construction")

Where there will be staircases or emergency exits on the surface in future, open construction will be used. The so-called cover construction method is used: First, bored piles or diaphragm walls made of reinforced concrete are constructed, between which the excavation pit is dug. As soon as the excavator and wheel loader have reached a depth at which they can work, the pit is sealed with a concrete cover. Construction materials are then transported in and out via smaller conveyor shafts that remain in place.

Our explanatory video shows how drilled piles work:

New Austrian tunnelling method

This construction method, which has been tried and tested over many years, is used, for example, when angled building sections have to be built. This also applies to the station tunnels, i.e. those sections of track where the platforms will later be. First, the ground is secured with steel spikes. Then the soil is excavated metre by metre and the resulting tunnel is reinforced with shotcrete on a steel grid.