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Influence of geology on tunnelling conditions and deformational behaviour of supports in faulted zones — A case history of the Chhibro-Khodri tunnel in India |
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| Authors: | JL Jethwa B Singh Bhawani Singh RS Mithal |
| Institution: | 1Central Mining Research Station, Dhanbad India 2Department of Civil Engineering, University of Roorkee, Roorkee India 3Department of Geology and Geophysics, University of Roorkee, Roorkee India |
| Abstract: | Construction of the Chhibro—Khodri Tunnel of the Yamuna Hydroelectric Scheme near Dehradun in the lower Himalayan region has been delayed by over six years due to problems associated with highly squeezing rock masses encountered unexpectedly in recurring faulted zones. Attempts to measure tectonic slip along a fault zone running across the tunnel have been reviewed. The suitability of a “flexible lining” provided in this zone has been evaluated in view of the region being seismically active. A tunnel instrumentation programme was implemented to evolve a flexible support system capable of reducing rock loads to manageable levels in highly squeezing rock conditions. Use of “loose” backfill with steel-arch supports has shown promise in this direction. Observed support pressures have been compared with the estimated values for evaluating the empirical and theoretical approaches of rock-load assessment in the squeezing rock conditions. The elasto-plastic theory has yielded reliable estimates of rock pressures. |
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