ABSTRACT
Twin 10 km long parallel headrace tunnels were excavated as part of the headrace tunnel system for the Neelum Jhelum Hydroelectric Project, using two Tunnel Boring Machines (TBMs). The permanent support normally comprised a shotcrete lining applied over initial support elements. However, concrete lining was required in certain areas of extremely poor ground conditions. Once placement of conventionally reinforced concrete commenced, it was found to be taking longer than anticipated, prompting a search for alternative solutions. Steel Fibre Reinforced Concrete (SFRC) proved to be the most viable option for accelerating the concrete lining programme. This paper briefly outlines the requirement for a concrete lining in the aforementioned areas. It includes an assessment of the suitability of a conventionally reinforced concrete lining versus an SFRC lining, the design basis, and the actual design itself. A comparison of the costs and durations to install the two types of lining is also presented.
