Characterization of Pare Rock Mass and Support System Design for Head Race Tunnel

Abstract

The Head Race Tunnel (HRT) of Pare Hydro-Electric Power Project in Arunachal Pradesh, India, traverses through the Upper-Siwalik Sub-Group of the Sub-Himalayan Range, exhibiting spatial heterogeneity with respect to geotechnical and geological properties. In such complex geological set up, consisting of bedding planes, joints, fractures,varied hydrological conditions etc., prediction of rock mass quality or the characterization of the rock massis a difficult task. Although challenging, it is important to predict the general response of the rock massto tunnel excavation. This paper attempts to characterize Pare Rock Mass around the HRT, based on Rock Quality Designation (RQD), Terzaghi’s Rock Load Theory, Rock Structure Rating (RSR), Rock Mass Rating (RMR), and, Rock Mass Quality (Q) system. An attempt is also made to design the support system for HRT through Pare Rock Mass, based on these parameters. A critical examination of various support systems derived from the above mentioned methods and the support system actually provided at the HRT at Pare Hydroelectric Power Project is also presented in the paper. The study presented in this paper will providean insight about the suitability of a particular method in the design of support system in a rock mass similar to Pare rock mass.