The JV excavating the new metro link tunnels in Leipzig, Germany, reports that 115 rings had been built on the twin bore tunnel by the end of March and that the TBM is on schedule for the first breakthrough, at Wilhelm Leuschner Platz, in May.
The contractor, Arge Tunnel- und Ingenieurbau Leipzig Los B, said that the 9m diameter Herrenknecht Mixshield TBM has been averaging about 10 rings per day since boring began mid-January from the open box for Bayerischer Bahnhof station. It had erected 74 of the 1.8m long, 400mm thick rings – (7+1) precast segments, 7.9m i.d. – by 20 March.
The TBM will be used to drive both tubes through formations including glacial till, clay, river gravel and sandstone with cover varying from 8m-16m. The 1100t Mixshield TBM is 65m long, has 17” cutters (six double, 36 single) and the cutterhead power is 880kW, torque is 7255kNm, and the total thrust the machine can exert is 55,000kN.
Lot B is budgeted at US$202M and includes construction of the twin bore tunnels, each 1.48km long, and four box stations in the tight urban setting. The project has called for extensive ground investigation and preparations, extensive monitoring including archeological investigations and removal of cable anchors from the path of the future tube (T&TI, December 2006, p22). Sixteen shafts were sunk to undertake ground treatment, including compensation grouting.
Construction of the four stations began three years ago. Both the Bayerischer Bahnhof box (85,700m3 – in total almost 200m long) and the biggest, the Wilhelm Leuschner Platz box (88,500m3 – 163.9m long), have been fully excavated to depths of 17m and 24m, respectively – the latter below ground slab.
The other stations are more than half excavated below slabs – 14m of 24m full depth at Markt (to be 75,200m3 – 144.6m long ), and 10m of 17m at the main station, the Hauptbanhof (to be 37,000m3 – 95.1m long). The boxes are being dug out with Cat 385 C excavators.
The JV dealing with the tunnelling and logistical challenge in Leipzig consists of technical leader Dywidag Bau, commercial leader Alpine Bau Deutschland, and also Oevermann and Strabag.
Two other packages on the project are Lot A, for the South entrance to the tunnels, and Lot C, for the North and West entrances and construction of extra works at Hauptbahnhof.
The total length of the project is about 5.3km and the budget, including finishing and railworks to is about US$755M. The client has said that the service is to become operational in 2010.
Funding is budgeted to come primarily from the state of Saxony/Leipzig city, the EU and the federal government. However, debate is running over demands from opposition politicians in Saxony after the key state politician who backed the scheme moved up to a federal role.
