From the magazine, Microtunnelling, Pipe jacking, Tunnelling

Major pipe jacking in Warsaw

In many large cities, wastewater systems have reached their limits, requiring modernisation or expansion in order to avoid overflowing into nearby rivers. For this reason, the City of Warsaw began the construction of a new state-of-the-art wastewater treatment system in 2010.

Hydrobudowa, PRG Metro and KWG were commissioned to connect the plant with the underground wastewater network. The contractors utilised two Herrenknecht AVND machines to complete pipe jacking works required for the connection.

The Herrenknecht AVND machines handled the difficult drives, with a total length of 5,860 m, with ease. As well as pipe jacking large diameters of 3 m, the extreme winter conditions and a high groundwater level demanded top performance by everyone involved. Achieving drives of up to 36 m a day, the Herrenknecht machines blazed the trail for an efficient new wastewater system in the Polish capital quickly and efficiently.

Project challenges

The high groundwater level, which in some places reached up to 8 m above the top of the pipes, was a significant challenge on the project. The site teams were obliged to dewater and seal the requisite construction shafts prior to tunnelling. The Herrenknecht AVND machines proved their worth during this process.

Where required, these machines secure the tunnel face using a support fluid, such as a bentonite and water mixture, and an additional compressed air cushion in the split excavation chamber, allowing safe tunnelling under water pressure.

During the particularly cold winter months, the site team continued tunnelling work despite some extremely low temperatures and a lengthy period of frost. The machines completed a total of 16 drives, some with short distances starting at 80 m, but also including long-distance sections of 800 m and more.

The longest individual drive was 930 m, during which the machines safely passed under a six lane highway without any negative impact on the flow of traffic.

This section also involved two underground curves with a radius of 450 m and 900 m. Thanks to the Herrenknecht SLS RV navigation system, the cutterhead was guided with millimeter precision.

To complete the entire sewer system and connect it with the new wastewater treatment plant, Hydrobudowa and PRG Metro are also completing a 1,300 m long tunnel with a Herrenknecht tunnel boring machine. Once this tunnel is completed the wastewater treatment plant will go into operation.

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