Construction challenges for urban tunnelling - The Copenhagen Metro Circle Line

The Cityringen (The City Circle) project is the latest phase of the metro system in Copenhagen, Denmark. The phase comprises the construction of 17 new stations, three shafts, a control and maintenance centre and 16.5 km of twin-tube tunnel excavated by four Earth Pressure Balance TBMs. The design and build contract was awarded in January 2011 and inauguration is planned for late 2018.
The geology in the project area includes 10 to 30 m of Quaternary sand, gravel and clay tills underlain by limestone, often containing benches of flint or other hard horizons. The stations and shafts are constructed with secant pile walls or diaphragm walls. Permeation grouting is undertaken for one cavern and grouting for the break-in and break-out of the TBMs.
Groundwater control is carried out by pumping from abstraction wells at the bottom of the deep excavation, treating the abstracted groundwater and recharging between 95 and 100 % of the groundwater.
A monitoring system consisting of a comprehensive database system has been adopted, where real time information from the TBMs and from buildings and structures adjacent to the works is collected. Movement is monitored by an extensive 3D monitoring system together with extensometers, inclinometers and piezometers.