Application of the NATM Methodology for the Excavation of Rail Tunnel in Difficult Geological Conditions: A Case from Garhwal Himalaya, Uttarakhand

The documentation of excavation method and support design based on rock mass classification systems i.e. rock mass rating (RMR), Q-system and New Austrian tunneling method (NATM) for adit-7 tunnel being constructed in Garhwal Himalaya, India is discussed in this paper. The New Austrian tunneling method classes of rock units have been developed by using correlations with the RMR and Q systems, according to the ONORM B 2203. NATM principles were used because the geological conditions were continually changing. The study indicated that the RMR-based rock mass estimation was overstated, but the qualitative assessment was right. The NATM technique is more adaptable for Garhwal Himalayan rocks having various uncertainties in rock mass evaluation. The current adit investigations indicate that there are numerous unanswered concerns, concerning rock mass quality evaluation, tunnel behavior during construction and usability. Results of the analysis are considered to be useful for the design of the new tunnels constructed in the similar type of the terrain.