Rock Grouting in Copenhagen Limestone - The Cityringen Experience

Extensive rock grouting has been carried out during the construction phase of the Cityringen Metro Project. The main goal of the rock grouting has been to reduce the permeability in the rock by filling joints, cracks and fissures, in order to minimize the groundwater inflow during excavation of caverns, pump sumps and TBM break in/out through the stations/shafts. Both horizontal and vertical grouting has been performed above and below the water table, with unique challenges and advantages/disadvantages. The grouting has been performed as up-stage, where the grout hole is drilled to full depth and then grouted from the bottom and up in stages using a pneumatic packer. The split-spacing method has been used to expand the grouting pattern if needed after primary grouting campaign has been finished and tested. The article describes, through case histories, the achieved results, challenges and limits of the applied methods, including future recommendations. The rock characteristics of the Copenhagen limestone, in regards to the performed rock grouting, are also discussed.