The St. Kanzian Chain of Tunnels -Tunnelling under very varied and extremely difficult conditions Tunnelkette St. Kanzian -Tunnelbau unter sehr unterschiedlichen und extrem schwierigen BedingungenIn the course of the building of the new Koralmbahn railway line between Graz and Klagenfurt in Austria, six tunnels have to be built in a sensitive landscape on the Carithian side. The tunnels have lengths of between 230 and 2,100 m. All the tunnels are designed to resist water under pressure and have a two-track standard cross-section. Except for the 495 m long Kühnsdorf Green Tunnel, which has already been completed, all the tunnels are currently under construction. The Srejach and Untersammelsdorf Tunnels with lengths of 620 and 665 m respectively are being driven in very challenging ground conditions consisting of silty to fine sandy lacustrine sediments, and extensive specialised civil engineering works had to be carried out in advance of both these tunnels. The performance of extensive tests and investigations during the tendering phase turned out to be very valuable for the planning of the project. The longest tunnel, the Stein Tunnel with a length of 2,100 m, is characterised by its location in soft ground with shallow overburden and the sensitive hydrogeological and ecological conditions. The driving of the Lind Tunnel in phyllite required special measures due to the lacustrine sediments above the tunnel, which reached down to the tunnel crown.
The St. Kanzian tunnel chain lies near the Völkermarkt reservoir and is part of the Mittlern-Althofen approval section of the Koralmbahn line in Carinthia. Of the six tunnels in the St. Kanzian tunnel chain, the 495 m long Kühnsdorf green tunnel (cut-andcover) has already been completed. The construction of the 230 m long Peratschitzen green tunnel (a cut-and-cover noise protection tunnel) and the 620 m long Srejach Tunnel (top-down construction) started in summer 2015. Work should start on the Untersammelsdorf, Stein and Lind Tunnels (all mined tunnels), in spring/summer 2016. The tunnels lie partially in challenging geological conditions (lacustrine sediments), all with shallow overburden, and require special measures for support and ground improvement (bored piles, jet grouting). Particular attention has been paid to later maintenance costs, which have to be considered in the course of the design work.
In the course of constructing the new Vienna -St. Pölten highspeed railway line, three TBM tunnels with an excavated diameter of approx. 13 m were driven between 2005 and 2010. The total length of these three tunnels including portal structures, cut-andcover and top-down sections was approx. 7.4 km, of which 6.2 km were excavated by TBM-S. The tunnels were constructed with drainage systems and two-pass linings in the tunnel arch. During the feasibility study, the permit application design and the tender design phase, detailed risk analyses were performed for excavation method (TBM or NATM), machine type (TBM-S or SM-EPB) and lining type (single-or two-pass). The expectations of the client during the design phase and those of the contractor during the bidding phase are compared and discussed, taking into account construction time considerations, geotechnical risk assessments, lining design, machine type and construction sequence as well as the allocation of risks between client and contractor. The reality of the project, i.e. the construction time actually needed, the challenges encountered, the problems solved and the joint approach adopted to implement the project as well as the lessons learned (experiences and findings) are all described.
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