The Design of Mountainous and Sub-sea Tunnels as Climate Resilient Infrastructures Using the Norwegian Method of Tunnelling (NMT)

The Norwegian Geotechnical Institute (NGI) has performed numerous studies over the past two to three decades on design of underground works for mountainous and sub-sea tunnels in Norway and abroad. These infrastructures are considered as both climate resilient and environmentally friendly when applying the principles of Norwegian Method of Tunnelling (NMT). The NMT minimizes the use of concrete resulting in reduced CO2 footprint. The Norwegian Method is a single shell design method in contrast to the New Austrian Tunnelling Method (NATM) double shell design method which is much more expensive and uses more concrete. NMT is based on the application of the NGI developed Q-system of rock mass classification for rock support design and emphasizes the application of a single shell rock support as final lining. This paper describes with examples the design of rock support for tunnels in mountainous and subsea tunnels which have been constructed in Norway. Both the empirical (Q-system) and numerical techniques have been combined for selecting and optimizing the rock support, respectively. The Q-system is utilized to build up a picture of the composition and characteristics of the rock mass and to provide estimates of support requirements and strength and deformation properties of the rock mass. Through an evaluation of all accessible data, a three-dimensional geologic excavation is usually converted into an idealized two-dimensional model for numerical simulation. This combination of empirical and numerical approaches results in saving of time and costs for tunnelling. The study thereby demonstrates the usefulness of employing such techniques to a host of rock mass conditions which can vary from extremely poor to very good rock conditions.