Abstract

The Norwegian Method of Tunnelling (NMT) is single shell tunnelling in contrast to the double shell tunnelling often called the New Austrian Method of Tunnelling (NATM). A key feature of NMT is the application of NGI developed Q-system for rock mass classification for selecting the rock reinforcement requirements in a tunnel. These rock reinforcements are often verified and checked using a numerical approach which allows optimization of tunnel support resulting in savings of time and costs during tunnelling.

This paper describes the application of rock mass classification 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 converted into an idealized two-dimensional model for numerical simulation. The empirical and numerical approaches are thus combined and the rock support recommendations prescribed by the Q-system are examined.

A case study of a road tunnel is presented where it is shown that tunnel reinforcement in the numerical model, as prescribed by the updated Q-system effectively stabilizes the rock using fibre reinforced shotcrete and bolts. The study demonstrates the usefulness of employing such principles to a host of rock conditions in different parts of the world including Vietnam where there are plans to build new road and rail tunnels for improving the communication links in the country.

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