COMPARISON BETWEEN PREDICTED ROCK MASS CLASSES AND ACTUAL ROCK MASS CLASSES IN HEADRACE TUNNEL OF MEWA KHOLA HYDROELECTRIC PROJECT, NEPAL

This study involves comparison of predicted rock mass classes in the design stage with actual rock mass classes pressurized head race tunnel Mewa Khola Hydroelectric Project. The headrace tunnel is 5m wide, and 5 m high and has a 22.32 m² area of inverted D-shaped cross-section. The total length of the headrace tunnel is 4801 m. The velocity in the headrace tunnel will be nearly 1.48 m/s during design flow. The Project area is situated in the lesser Himalayan meta‐sedimentary rocks. The main rock types found in the project area are Phyllite, Schist (somewhere garnetiferous), and gneisses. The rock mass classifications and Q-system were used to predict rock mass classes during the design phase as well as for classify rock mass during the excavation of the headrace tunnel. The applicability and validity of the proposed classification have been checked by comparing the prediction with actual observation after the completion of excavation. It was found that the predicted classes do not exactly match with the actual rock masses as a result affecting the construction time as well as in cost and economy of the project.

Keywords: Comparison, Geology, Actual rock mass, predicted rock mass, headrace tunnel.