Nearly 6km of 3m diameter pipejacking plus a larger diameter segmentally lined drive under the river has blazed the trail for an efficient new wastewater system in Poland's capital city. Two Herrenknecht AVND micromachines and their crews worked through extreme winter conditions and under high groundwater levels and demanded top performance by everyone involved. With progress rates of up to 36m a day, the micro-drives were completed on time and ready for start this week of the river crossing drive.
Ready to go - the Herrenknecht AVND2400AB
Warsaw has invested in construction of a new state-of-the-art wastewater treatment system to modernize and expand existing facilities and avoid overflows into nearby rivers. The new system will treat wastewater produced by 80% of Warsaw's inhabitants to improve the quality of water, and of life, along the banks of the Vistula.
Hydrobudowa 9 S.A., PRG Metro Sp.z.o.o. and 'tWVG (PBG Group) have been commissioned to build the underground wastewater network and connect it to the new Czajka wastewater treatment plant. The Polish contractors selected the pipejacking method for their tunnel project and relied on two hydroshields from Herrenknecht to bore 5,860m through demanding conditions.
70% coarse and fine sand, 30% clay and loam, gravel, boulders
16 drives of 80m to 930m long for a total 5,860m
High groundwater level, long 3m diameter drives, curved drives
The AVND2000AB and AVND2400AB, with extension kits to 0 3,025mm, tunnelled at depths of 10m to 14m and reaching their final targets after boring through soil comprising coarse and fine sand, clay, loam, gravel and boulders.
Apart from the unusually large 3m diameter for pipejacking, the Herrenknecht machines completed a total 16 drives, some as short as 80m and others up to 800m and more. The longest individual drive was 930m. During their operation the hydroshields safely underpassed a six-lane highway without any negative impact on the traffic. During the particularly cold winter months of 2010, the site team continued tunnelling work despite some extremely low temperatures and a lengthy period of frost.
M-1 083M, AVND2000AB with extension kit to 3,025mm diameter
M-1363M, AVND2400AB, with extension kit to 3,025mm diameter
Mixed-soil cutterheads fitted with disc cutters and pick tools
Another challenge was the high groundwater levels, reaching up to 8m above the top of the pipes in places. Dewatering of the ground around the construction shafts was required prior to tunnelling. The hydroshields supported the tunnel face using the bentonite slurry and the compressed air cushion in the split excavation chamber of the hydroshield systems. The Herrenknecht separation plant HSP500, provided a slurry processing capacity of 400m3/h to 500m3/h, depending on the particle size distribution.
Hydraulic intermediate jacking stations were installed to reduce the friction forces in the longer tunnel drives. These interjack stations were modified by Herrenknecht to fit the thin walls of the Hobas GRP pipes installed in Warsaw. The longest drive revealed yet another particular feature: two curves with a radius of 450m and 900m respectively.
The Herrenknecht SLS RV navigation system guided the micromachine cutterhead to within millimeter precision, with the machine operators mastering the systems in a precise and safe manner.
December 14, 2010 saw completion of the last drive for the project, representing a significant milestone for wastewater management in Warsaw. During the construction project, the Herrenknecht equipment achieved advance rates of up to 36m a day of two shifts and an average of 20m/day.
16 drives in the new network
Mixshield S-642 accepted for the Vistula River crossing
To complete the entire sewer system and connect it with the new Czajka treatment plant, PRG Metro Sp.z.o.o. and Hydrobudowa 9 S.A. will now complete the 1,300m long Vistula River crossing with a Herrenknecht Mixshield of 5.35m diameter. The machine was accepted for delivery from the Schwanau works in February 2011 and headed out on its under river drive this week. Once this tunnel is complete the Czajka plant will go into operation.
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