STABILITY ASSESSMENT OF THE UNDERGROUND CAVERNS FOR THE ETALIN HYDROELECTRIC PROJECT, INDIA

Abstract

In this thesis an attempt has been made to apply the Norwegian design principles for alternate design of unlined / shotcrete lined tunnel for Head Race Tunnels of Etalin Hydroelectric project, India. The detailed stability analysis of underground powerhouse is done using empirical, analytical and numerical methods.A study has been done to assess the cost optimisation by taking into account the reduction in cost of lining and increase in cost due to increased cost of excavation and rock support. Hydraulic equivalent section has been used in cost optimisation calculations Stability analysis of the underground power house complex of Etalin hydroelectric project consisting of three caverns housing powerhouse, transformer and surge chamber is done and rock support designed. The power house has three caverns located at a depth of 400m aligned parallel at a spacing of 50m. The size of powerhouse cavern is 352m (L) x 23.5m (W) x 59.73m (H). The total size of transformer cavern is 349.6m (L) x 16.5m (W) x 24.3m (H). Downstream surge chambers of size 165m (L) x 13m (W) x 46m (H) for Dri limb and 110m (L) x 13m (W) x 46m (H) for Tangon limb are provided. The empirical methods include basic rock mass classification methods such as RQD, Q-system, RMR and GSI method based on the field investigation data and geological mapping records. .Rock support design also done suing Q-system. Engineering and mechanical properties of intact rock were recorded from the laboratory tests on rock core samples from drill holes. Rock mass strength and modulus values have been calculated using various empirical relations. The Hoek and Brown rock mass strength parameters were determined using Roclab program. The analytical methods include assessment of stress related problems by calculation of tangential stress using Kirsch s analogy, Hoek and Brown practical method. Rock burst impact depth is calculated form Martin and Christiansson. The adequacy of width of rock pillar was verified using Brown and Brady s tributary area theory and with the help of Martin and Maybee s study on rock pillars.The numerical methods include Unwedge and Phase2 programs. Unwedge is used to determine potential wedge failures and spot bolting design for stabilising the wedges. The Phase2 program has been used to find the principal stress situation, displacemnts, strength factor, volumetric strain, yield zone and rock support design. The numerical modelling has been modelled for varying in-situ stress situations, varying rock mass quality, boundary conditions, and support types in modelling.