Mitigation works prior to soft ground tunnelling with low cover for the Copenhagen Cityringen Metro
The Copenhagen Cityringen is currently under construction and due to expand the current Metro system by 17 new stations in 2019. The Cityringen crossing above the existing Metro tunnels at Kongens Nytorv in Copenhagen, Denmark necessitates shallow tunnelling in soft ground with EPB tunnel boring machines, beneath heritage buildings on shallow foundations in the historic centre of the city. The Contractor proposed mitigation works comprising a combination of alignment adjustment, localised underpinning by jet grouting, preparation for compensation grouting in case of settlements, and preparation for emergency dewatering in case of TBM face intervention. This paper will discuss the mitigation measures chosen, the issues encountered on site during installation and the resulting effectiveness of the mitigation measures during TBM passage.