Malmö TBMs hole through

Both TBMs driving the twin tubes for the Citytunneln project in Malmö, Sweden, have holed through to complete their first, 2.7km long, drives.

The double breakthroughs at Triangeln station occurred one month apart, in late August and late September, respectively. The second 8.89m diameter Herrenknecht EPBM – “Katrin” – covered the distance a month faster than the first shield, “Anna”.

While further progress data for “Katrin” were not immediately available, its sister machine - after passing through the learning curve - achieved a best day’s progress of more than 30m, best week of almost 150m and the average daily rate was over 12m. “Anna” was launched in November 2006, “Katrin” just over eight months ago. When “Anna” holed through in August, “Katrin” had 600m to go and was expected to take up to another two months to finish, but took much less.

Geology along the tunnel alignments is limestone, and groundwater is almost 20m above the tunnel invert. The drives are at depths of 20m-25m, and the total length of each will be 4.6km, the tubes separated some 10m-30m along the route. Dewatering is only being used at the stations and TBM launch pit. The 7.9m i.d. tunnel is segmentally lined (7+1) with the 1.8m long rings having o.d. of 8.6m.

The breakthroughs are almost at the halfway stage of excavation on the project and the programme is on schedule. However, more complicated tunnelling lies ahead as the TBMs approach Malmö central station.

Before they resume their drives, “Anna” again setting off first, probably around November, the TBMs are undergoing maintenance and repairs including replacement of scrapers and cutting discs. The drives are due to finish by the third quarter of 2008, and the entire project by 2011.

The drives are being constructed by Malmö Citytunnel Group, a JV of Bilfinger Berger, Per Aarsleff and E Phil & Sons under a US$325M (2001 prices) design and build contract. The client is the National Rail Administration (Baneverket).

The US$1.3bn (2001 prices) transport project - a third of which is below Malmö - will link the city’s rail system with the Öresund bridge to Copenhagen, Denmark. The project also includes a link to the Scania rail network (T&TI, March, p18-21).

'Katrin' holes through in September 'Katrin' holes through 'Anna' is first to hole through, in August 'Anna' is first to hole through