TBM-spoil characterization and utilization at the Follo Line project

The potential use of surplus materials commonly considered as waste has been investigated by the project “Geomaterials in the Circular Economy” (GEOreCIRC). TBM spoil is one of the materials which were assessed, based on data from the Follo Line tunnel project in Oslo, Norway. For this tunnel, four TBMs were used simultaneously and the tunnel generated almost 9 million metric tonnes of spoil. The excavated TBM spoil was used to establish a building platform for a new district in the Oslo municipality, by filling a 30 m deep valley. An extensive campaign of laboratory testing, field measurements and monitoring was conducted for the deposit. The geotechnical properties, such as grain size distribution, grain shape, brittleness, density, permeability and friction angle were determined. The optimal water content for compaction and maximum dry density were determined using the Standard Proctor test. Field measurements included plate load tests and nuclear density gauge (Troxler), with several measurements for each layer of the deposit. In addition, the spoil was analysed for a wide range of possible contaminants associated with natural rock minerals and machinery used in the tunnelling process. The results show that the level of contamination is low, and related to background levels from the bedrock itself, with levels below specified threshold values for contaminated soil according to Norwegian regulations.