Celebrating end of TBM boring on Cityringen metro project

Main tunnelling work on the Cityringen metro project in Copenhagen has been completed with the remaining three TBMs completing their drives.

TunnelTalk reported the first of the schedule of finishes for the four 5.78m diameter EPBMs on the project in January.

Tunnelling for the twin 15.5km long running tunnels was performed by Seli Tunneling Denmark, part of the Salini Impregilo group and in mid-February, the Danish Prime Minister, Lars Løkke Rasmussen, celebrated the milestone progress at the project site with metro owner, developer and operator Metroselskabet and the contractors.

Metroselskabet says the new circle line and its 17 underground stations to serve in the heart of the Danish capital should be completed in mid-2019.

The first of four TBMs on the Cityringen metro project in Copenhagen has achieved a milestone completion. The EPBM breakthrough marks the first of a flurry of finishes that should see all four shields on the subcontract completing their drives by mid-February, explained Valerio Violo, Managing Director of Seli Tunneling Denmark ApS.

Final breakthrough for first of four EPBMs on Cityringen

The 5.78m diameter EPBM TBM-3 completed its 5km long final drive in the north section of the project, at Øster Søgade, in mid-December. Its sister shield, TBM-4, has been driving the parallel running tunnel through soft ground from Nørrebro Parken and Violo told TunnelTalk that it is expected to breakthrough within days of the first.

Both machines were manufactured in a purpose equipped facility in Nordhavn, in the Danish capital. They have each completed two drives, the first in the south towards Copenhagen central station and starting in 2013, and were relaunched for the second drives in the north section.

While these two EPBMs were made in Denmark, the other two machines on the project were manufactured in Italy. All are based on Kawasaki-Seli designs and are equipped with 17in cutters and rippers from Palmieri and other tools, bucket tips and cutter bits from Bewarder.

The Cityringen is a 15.5kmunderground metro loop line developed by owner and operator Metroselskabet, which contracted the Copenhagen Metro Team (CMT) JV, led by Salini Impregilo for its construction. Tunnel boring is being performed by Seli Tunneling Denmark under a subcontract to CMT.

Crews celebrate successful end of boring for TBM 3

The parallel north section drives were “the most difficult”, said Violo, including passing through 2km of soft ground comprising sand, sandy tills and glacial deposits. There were also “episodes” of CO and NH3 contaminants encountered and also some HCN. These required retro-fitting of the machines to handle the unexpected conditions.

The contractor overcame the challenges via a combination of

• keeping settlement “very low”;
• maintaining volume loss below the expected value;
• working with train-based mucking out due to length and the radius curves of the tunnels; and, handling frequent hole-throughs and then pull-throughs at box stations.

In the longer, north section, the tools and cutters performed well in the hard limestone and flint, which is notable given the challenges met with flint in previous metro construction in the city, said Violo. During the second drives the excavation diameter and the cutterhead tool configuration was adjusted for the soft ground, and articulation of the tail shield was modified to overcome challenges for advancing under some conditions.

Tunnelling almost over on Cityringen

The TBMs were able to achieve best progress rates of up to 34m/day and 174m/week, said Violo. “Record monthly advance was 734m, achieved by TBM-4, working three shifts/day, six days/week with Sunday reserved typically for maintenance,” he said. “The drives saw very constant and solid production.”

Lining is formed of five 300mm thick segments and a key in 1.4m long rings for a 4.9m i.d. running tunnels. Segment production was subcontracted to Mobilbaustoffe. Two-component grout was employed with custom-made rotary pumps which achieved “excellent results” said Violo.

The contractor’s other two EPBMs, TBM 1 and 2, are due to complete their 4km long, final drives drives at Copenhagen Central Station within the next few weeks (Fig 1). The CMT JV has already completed all excavation for the project’s 17 underground stations, and has excavation of the running tunnel cross passages underway.

During the course of the project Seli Tunneling Denmark was acquired by Salini Impregilo, becoming a division within the major Italian group. The acquisition in 2015 followed the restructuring of Seli SpA.