Tunnel excavation with D&B: the Skottås Tunnel case study

Drill and blast still features among the most used solutions for tunnelling in medium to hard rock conditions. The main benefits of this method are the versatile equipment, the fast start up and a relatively low capital tied to the equipment. It is a cyclical process that requires a proper work site organization. The aim of this work is to describe the application of D&B method for the excavation of Skottås Tunnel, in the southwest of Norway. Particular attention has been given to two specific activities, grouting injection before excavation and overbreak remedy actions before the final lining phases. The first one, also due to the geological conditions of Scandinavia, is a widely spread solution in Norway. The purpose of pre – grouting activity will be highlighted and what are the effects of this activity on the working area, but also on the rock mass that is going to be excavated. All the steps, from the drilling phases till the injection activity, are going to be analysed. As for the overbreak remedy actions, will take in consideration all the evaluations and the solutions will be taken in consideration, to manage the problem in the first 280 m of tunnel.