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Design and construction of cast in-situ steel fibre reinforced concrete headrace tunnels for the Neelum Jhelum Hydroelectric project

B. Ashcroft, G. Peach & J. Mierzejewski
Multiconsult Norge AS, Oslo, Norway
B. De Rivaz & M. Yerlikaya
Bekaert, Kortrijk, Belgium

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.