Challenges and new developments in hard rock tunnelling in Norway – Case studies

Hard rock conditions in Norway have posed great opportunities and advantages for the design and construction of many tunnel kilometres for many decades, which has normally been accompanied by technological developments. During the latest decades, however, limited research and advancements of practical significance have been implemented in support strategies. This primarily affects the extensive – and unquestioned – use of empirical rock mass classification systems for permanent rock support design in poor rock mass conditions, and the traditional use of uneconomic inner concrete liners to keep sheet waterproofing membranes in place in traffic tunnels affected by water seepages. Based on recently published research work carried out at NTNU Norway and the study of real tunnel construction sites of hard rock tunnels, the authors present in this article some of the main insights about modern and improved support design and waterproofing strategies aiming at economic and optimal support solutions. The presented approaches essentially combine the use of hybrid support design strategies and the implementation of sprayed concrete and pre‐excavation grouting as a measure to reduce water leakage, hence increasing concrete durability and support performance. The combined use of such hybrid approach for support design and the substitution of cast concrete lining by high‐quality sprayed concrete and rock mass grouting has provided satisfactory and optimised results.