Application of Rock Mass Classification Systems for future excavation and support design of proposed Road Tunnel from Khand Birkot to Sarot Doman in Tehri Garhwal District, Uttarakhand

Tunnel is a fundamental element of the nation's infrastructure and the mighty Himalayas have the vast potential of underground construction of tunneling for transport systems and hydropower, etc. The present paper has been focused to propose a tunnel for the high-speed road link between Khand Birkot and Sarot Doman. The proposed tunnel will be about 4.3 km long, having a maximum overburden of 313 m and will pass through the complex Lesser Himalayan rocks. This work evaluates geotechnical conditions of the area by the rock mass rating (RMR) parameters in order to suggest support systems along the tunnel alignment. This procedure could be reliable for future tunnel construction and for suggestions of tunnel support design in the complex Lesser Himalayan region. The RMR results reveal that the proposed tunnel could be excavated by two methods in the area, i.e. the top heading and benching method with the 1.5-3 m advance or 1-1.5 m advance and the shield method for alluvium or unconsolidated overburden cover areas. The excavation methodology along the adits of tunnel and determination of the support system for the proposed adit alignments is also discussed.