The National Highway NH-21 in the Indian State of Himachal Pradesh is developed into a 4-lane divided dual carriageway. The road section between Chandigarh and Manali with a length of approximately 21 km is located in topographically very difficult terrain where the Beas River formed a deep and narrow canyon with high and steep rock slopes. The paper describes the challenges in the design and the construction of the EPC Contract for six tunnels with a total single bore length of approximately 20 km. This includes geological design, NATM excavation design and detailed structural design for the rock tunnels in different tectonic formations. The variable rock mass conditions in combination with the short lateral distance to the very steep canyon slopes resulted in demanding rock mass behaviour and various difficulties to be solved during excavations.
The National Highway NH-21 is located in north-western India and connects the cities Chandigarh and Manali in the State of Himachal Pradesh. The northern part of the highway, the section between Pandoh and Kullu, is in a topographically very difficult area where the Beas River formed a deep and narrow canyon with high and steep rocky slopes. The existing 2-lane highway of this 21 km long section has to be widened to a 4-lane divided dual carriageway which requires many tunnels, bridges, cuts and other structures in this particular section.
The National Highways Authority of India (NHAI) has awarded Shapoorji Pallonji as concessionaire who has appointed Afcons Infrastructure Ltd. as EPC contractor (engineering, procurement, and construction). The detailed design for the entire 21 km long highway section was done by the Joint Venture of SMEC India (SMEC) and 3G Gruppe Geotechnik Graz ZT GmbH Austria (3G) on behalf of the EPC contractor.
SMEC took responsibility for the alignment, open road, and bridge designs while 3G was responsible for the tunnel design of the 6 highway tunnels with lengths of 0.6 to 3 km. The 4 double tube tunnels and the 2 single tube tunnels have 3 lanes (2 carriageways and 1 emergency lane) and a total single bore length of approx. 20 km.
