Challenges of Tunnelling in the Capital Area of Iceland - Engineering Geological Evaluation of a Tunnel for a Proposed Fast Train Between Reykjavík and Keflavík

Abstract

As part of a possible railway connection from Reykjavík to the airport in Keflavík, an approximately 15 km long, single track tunnel, between Vatnsmýri and Straumsvík has been proposed. If built, this will be the first railway tunnel in Iceland. In this project report, an attempt was made to identify the main challenges of tunneling in Iceland and evaluate on how to cope with these. To do that, different existing project reports were studied. An evaluation of the degree of difficulty and investigation requirement for the project was done. Experiences from Norway and Sweden regarding waterproofing and permanent lining were reviewed, and both present day and future trends in technical solutions discussed, along with an innovative new method, using composite lining system. Fieldwork and engineering geological laboratory investigation was done on three rock samples, gathered in the field in Reykjavík, and compared to results from earlier projects. The three different rock types tested; móberg, grágrýti and modern lava, are the main rock types the planned railway tunnel will lie within, along with Elliðavogur sediments. A significant amount of time was spent gathering, sorting and analyzing borehole data from different projects. The information was used to create a 3D geologic/stratigraphic model of the bedrock in the capital area. Three modelling programs were tested; MicroStation, RockWorks and Leapfrog, with Leapfrog proving best suitable for the assignment. With further investigations in the capital area, new information and suggestions for adjustments are bound to come into light. This makes the benefits of having an easily updated and readymade interactive model, the more important. The thickness distribution of the rock mass in the capital area are was investigated, and from that, four different route options for the planned railway tunnel were suggested. An attempt was made to conclude what kind of rock support and sealing requirements could be suitable for the different rock types the tunnel will lie within, using the Q-value of each rock type.