The EU-commission recently launched a circular economy strategy in an effort to increase recycling and re-use of materials. The research project "GEOreCIRC – Georesources in a circular economy" at the Norwegian Geotechnical Institute aim to facilitate recycling and reutilization of various residual resources in an environmentally satisfactory way. The project is financed by the Research Council of Norway and will finish in 2019.
Traditionally, drill and blast has been used to excavate bedrock in Norwegian tunnelling projects. However, tunnel excavation using tunnel boring machines (TBM) can be cost-effective for larger tunnelling projects. The method is currently being used in a few Norwegian projects. The resulting spoil material from TBM-tunnelling has different particle size distribution compared to spoil from drill and blast tunnels. The amount of fine particles or fines is typically larger, leading to uncertainties regarding the sensitivity to change in water content, frost susceptibility and settlement properties of the material. As a consequence, the spoil has often been disposed of in landfills [JL1] without any further assessment as to possible areas of use. However, the GEOreCIRC project aims to investigate potential use of the spoil material, such as use in construction of a building platforms, by gaining more knowledge about the geotechnical properties of TBM spoil from different projects. Furthermore, the project will investigate the possible contaminations of the spoil, looking into potential risk for contaminant transport. Finally, the project aims to establish guidelines for testing of TBM spoils to aid possible reuse in future projects.
Environmental testing of samples from two recent Norwegian TBM-projects have been compared. These projects were chosen as special focus was given to ensure proper reuse of the resulting spoil material. For the Ulriken project, a TBM was used to establish a new railway tunnel just outside Bergen. The project is estimated to generate about 700.000 m3 of spoil, of which much is used to cover areas of polluted seabed in the port of Bergen. The Follo line project is currently Norway's largest infrastructure project. The project has four TBMs in use to excavate two new railway tunnels, just south of Oslo. This process is estimated to generate about 5.000.000 m3 of spoil. An agreement ensures that a large quantity of the spoil will be reused to establish a building platform for a future municipality in a valley in south east Oslo.
Overall, the environmental testing indicate that the level of contamination in the tested TBM spoil is low. The majority of the samples had concentrations of heavy metals and organic contaminants below the threshold level for contaminated soils according to Norwegian regulations. The background and important aspects of these results are further discussed.
Ongoing geotechnical testing includes the natural water content, grain size distribution as well as stiffness and strength properties of the materials. This is typically determined through the use of standard Proctor, oedometer and plate load tests. In addition, the permeability and frost susceptibility of the material will be studied.
Lessons learnt from practical projects , Proof of compliance - requirements and quality assurance , Development of testing methods and standardization
