Abstract
In recent years, the focus on feasibility studies for tunnels has increased in Norway. Traditionally, the refraction seismic method and the very low-frequency electromagnetic method (VLF-EM) have been used. The Geological Survey of Norway introduced the electrical resistivity traversing method (ERT) in feasibility studies for tunnel construction purposes. Resistivity modelling shows that the method has the potential to characterise fracture zones geometrically; i.e., the thickness, dip, and depth extent. Based on previous studies, a model for mineralogical characterisation is proposed. This model, and the possibility for geometrical characterisation, is critically tested with success on three tunnel projects. The results of the comparison study, with regards to weakness zones, show that VLF-EM is a method that is capable of locating fracture zones, while refraction seismic is capable of locating and indicating the width of the zone, and can be used to imply the thickness of the soil cover above bedrock. The 2D resistivity method is able to locate the weakness zone, indicate the width, depth extent, and the dip of the zone, and in addition, characterise the zone with respect to stability or water problems. The crystalline bedrock characterisation is divided into three groups: resistivity values above 3,000 Ω m indicating good rock quality, values between 3,000 and 500 Ω m indicating bedrock with mainly water problems, while values <500 Ω m indicate clay-bearing, unstable rock with fewer water problems. From our investigations, we conclude that the 2D resistivity method is a very good supplement to traditional methods for feasibility studies on tunnelling purposes in crystalline rock.
Highlights
Each year, more than 30 km of road and railroad tunnels in bedrock are constructed in Norway
Results from the Lunner tunnel is a classic example of resistivity values, characterisation of weakness zones, and bedrock quality
This study has shown that the resistivity (ERT) method can characterise rock quality and identify unstable rock masses, and based on the presented results we propose the following interpretation model for crystalline bedrock:
Summary
More than 30 km of road and railroad tunnels in bedrock are constructed in Norway This is done without any impact on the surrounding environment and within economical budgets, over the years a number of tunnelling projects have encountered significant problems. Such problems include encountering zones with major water leakage and substantial volumes of unstable rocks, resulting in extensive delays and considerable overspending during tunnel construction. One of the case studies in this project was the Lunner tunnel, Rv 35 in Oppland County (Fig. 1), which proved to be a success with respect to the 2D resistivity method as a supplement to traditional geophysical methods
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Bulletin of Engineering Geology and the Environment
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
