(Proceedings Workshop on Tunnelling in Himalayan Geology, 6–9 June 2006, Katra, J&K, pp. 160–175).
Dulhasti Hydroelectric project is located on the river Chenab in the eastern part of J&K state. Dam at Dul and powerhouse at Hasti is linked by 10.6 km long Head Race Tunnel (HRT) which remained a critical activity and bottleneck due to unprecedented geological problems and poor logistic supports. Excavation of HRY which was started in 1990, has been completed in 2003. The tunnel is currently being lined before being put in operation. Though the project was extensively investigated for a long period, a risk and uncertainty was felt till end which was dealt during tunnelling either through known methods or through locally developed devices as per site conditions. Sometimes, locally adopted measures are more successful in achieving the targets. It is learned with experience that the geological problems should be tackled in advance in a short time otherwise there would be lapse of time for treatment. On the other hand, basic logistic supports viz. proper ventilation, dewatering, lighting arrangements and adequate equipments are the lifelines during construction for speedy tunnelling. These supports become more important when the tunnel is to be excavated through water charged medium that too for a longer stretch. Numerous teachings are to be remembered from this experience, the main of which being our modesty previsions of actual geological conditions along tunnel excavated in such young, active mountain ranges. Therefore, geological investigations ahead of the tunnel face appears a necessity to detect weaknesses in rock mass and adequate means of treatments shall be made available for a cost and time saving excavation. This experience also pinpoints the importance of selecting the suitable TBM with the geological context.
