Maximum safety for the new Copenhagen Metro Line

The Copenhagen Metro Line is among the world’s most modern subway systems. To improve the infrastructure in the Danish capital, the city is now expanding its existing metro system by two-thirds through construction of the new “Cityringen” subway loop. Lines M3 and M4 are now being added to the existing M1 and M2 lines. Tunnel-building activities on such a scale in the heart of an old city harbour pose great potential risk due to the unfavourable geological conditions, limited coverage and proximity to existing development. To ensure structural stability throughout the construction phases, various geodetic and geotechnical measuring systems will be used for automatic monitoring in order to detect possible deformations in a timely manner, allowing immediate countermeasures to be initiated. Automated 3D measuring systems, which are installed at every station, shaft and along the stretches of tunnel,play a particularly important role in this.

The new lines include 17 new metro stations, three shafts with crossovers, and a new maintenance centre. The entire, approximately 15.5-kilometres long, route proceeds through two parallel tunnel tubes in the subsoil of Copenhagen. The new lines will finally connect the central station (København H) and east station (Østerport) to the metro system. Like the existing system, the new metro was also conceived as a driverless, fully automatic system.

The overall costs for the project amount to about 2 billion euros. The Copenhagen Ministry of Transport and the municipality of Frederiksberg are the owners of this major project, represented by Metroselskabet I/S. The executive consortium is an Italian joint venture consisting of Salini/Impregilo Tecnimont and SELI –  Copenhagen Metro Team (CMT).

A joint venture of GEODATA Ziviltechnikergesellschaft mbH and ANGERMEIER INGENIEURE GmbH received the contract for monitoring the entire project and founded their own new firm, SMT Denmark ApS, to carry out this enormous assignment.

SMT Denmark ApS is charged with the geodetic and geotechnical monitoring. This includes the precision levelling, conception, set up and servicing of automated 3D monitoring systems, and the installation and servicing of automatic inclinometers, strain and coders extensor metres, and water level gauge measuring systems. In addition, SMT Denmark ApS must also supervise KRONOS, the central project database, where all measurement results, including machine data transmitted every 30 seconds from the four tunnel boring machines (TBM), will be stored. Almost 30 employees are completely dedicated to the monitoring tasks in the Cityringen project.

In January 2012, a start was made to gradually equip all metro stations under construction and shafts with automated 3D measurement systems. Both tunnel tubes are being driven in parallel with the four TBMs. In the process, two offset machines each drive a specific route section in the new subway loop.

Since summer 2013, the tunnel sections have been equipped with measurement systems during the TBM drives. In the process, the individual total stations were connected into networks in order to reliably cover the planner’s prediction of possible settlements (also called zones of influence). In doing so, up to eight Leica TM30 total stations were connected into monitoring systems that are centrally controlled and monitored by a PC over WLAN.

Monitoring instruments from Leica Geosystems
Both of SMT Denmark ApS’s parent companies are long-standing, loyal customers of Leica Geosystems. The choice of supplier for the geodetic measuring instruments and accessories therefore fell on the Swiss premium manufacturer at the very beginning of the project. Over the duration of the project, this proved once again to be an excellent choice, as it was in earlier projects. The measuring instruments operate with such high accuracy that the 3D measuring system and the redundant levelling measurements, which were carried out with the Leica DNA03 level and 2-metre Invar staffs, matched within half a millimetre. The high quality of  measurement results contributed significantly to the project’s success.

60,000 noiseless measurements per day
The standard measurement frequency is every two hours for all automated measuring systems. In critical situations, the measuring frequency is reduced to one hour or 30 minutes, depending on the particular number of points to be measured.

A special case arose during the monitoring of existing metro tubes when the TBM had to cross the tunnel tubes. Here, the measurement frequency for 10 points actually had to be raised to every 90 seconds in order to be able to give constant feedback regarding settlement during the crossing.

The Software Observer, a proprietary software of ANGERMEIER INGENIEURE GmbH, controlled every total station. It automatically eliminates outliers during every measurement within a measurement cycle. All measurement values are then transferred to an adjustment software and processed. If the results are within the required range of accuracy, the coordinates and protocol are transferred to the KRONOS database, which is proprietary software by GEODATA Ziviltechnikergesellschaft mbH. If there is a data transmission failure or internal warning or alert levels are exceeded, for example, if the compensator values are outside specified accuracy range, immediate, automatic notifications are distributed to the predefined internal group of people.

Up to December 2014, 72 Leica TM30 total stations were installed at the 21 new structures. An average of up 21 total stations run in parallel along the tunnel routes. Approximately four months following completion of a section, they are taken down and reinstalled in the new section.

More than 4,000 prisms were installed with the total stations. Approximately 60,000 measurements per day. Overall, more than 44 million 3D measurements have been carried out so far. Similarly, there were also 600,000 manual levelling measurements.

The extremely low noise generation of Leica Geosystems total stations is certainly worth mentioning. They could easily be installed directly alongside bedroom windows without waking the residents from their sleep.

Continuous servicing of the total stations
Four employees are responsible for taking care of the total stations. Their tasks include troubleshooting malfunctions that arise in individual systems and installation of new systems in the station and tunnel sections. After passage of two tunnel boring machines has taken place, they must take down the sensors again. The 3D systems are still in operation at the metro stations under construction.

All computers are remotely accessible from a main centre, which is advantageous when needing to access the network. If an error cannot be corrected through remote maintenance, a local squad sets off to find the problem. Many of these malfunctions are caused by construction activities at the stations, such as interrupted power supplies or restricted visual communication with the reference and deformation prisms due to the large construction machines.

SMT Denmark ApS has added its own lifting platform on a 3.5-ton truck for the installation of prisms and total stations. This is the only way to be flexible and carry out installation and removal or exchange of equipment for maintenance.

Experienced teams – reliable systems
Operating such a large monitoring project for the benefit and safety of Copenhagen’s citizens and visitors is a great challenge for the entire team and the measuring system.

As far as the team is concerned, a great deal of experience is required here. Internal processes are continuously optimised. The software components in the Observer are also subject to continuous modifications due to the changing requirements for this complex monitoring project.

The instruments are subjected to a maximum demand for quality, reliability and precision. The demands on the employees, who quickly and confidently respond to every malfunction that arises, are equally high. Monitoring sensors from Leica Geosystems are the perfect partners for this enormous task.

Written by Dieter Heinz