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H.G. Jodl, G. Altinger, I. Heegemann, A. Jurecka:
"Selected construction solutions on tunelling Vienna underground line extension U2";
Talk: Jubilee Scientific Conference 65 years University of Architecture, civil engineering and geodesy, Sofia, Bulgarien (invited); 2007-05-17 - 2007-05-18; in: "Jubilee scientific conference - 65 years University of Architecture Civil Engineering and Geodesy", (2007), 37 - 46.

SELECTED CONSTRUCTION SOLUTIONS ON TUNWELLING VIENNA UNDERGROUND LINE EXTENSION U2
The extension of the Underground line U2 is due to existing hydro-geological conditions and because of the crossing of the river "Donaukanal" posing a challenge to all participants involved in this project.
The crossing of the "Donaukanal", which is a river with a width of abaut 50 meters,was achieved within the contract section U2/1 using the method of graund freezing. Both common techniques of nitrogen freezing and brine freezing have been applied in combination first time.
In order to ensure an area-wide lowering of the groundwater - within the contract section U2/2 - 240 wells had to be drilled each with a depth of about 40 meters. Due to the high number of wells a regulation and control system has been installed. This system assures an overview from a central place on the current capacity of each pump and may warn the responsible technician in case of failures. It moreover helps to process and analyze thee large amount of data.
Jet grouting was used to build protection shields against uncontrollable water ingress both from the tunnel as well as from the surface. The intention was to ensure safe tunnelling conditions and to facilitate driving. When erecting the shields from the tunnel head,
excavation could only be done alternately. From the surface it was possible to jet grout in advance to the heading and hence save time. Major parts of the jet grouting were not included in the original contracts. In some places the hardly predictable circumstances of the
ground made it necessary, in other parts a shortening of construction duration could be achieved through amicable adjustment of the contract.

http://publik.tuwien.ac.at/files/pub-bi_7210.pdf