Fluid Flow and Leakage Assessment Through an Unlined/Shotcrete Lined Pressure Tunnel: A Case from Nepal Himalaya

Abstract The use of unlined/shotcrete lined pressure tunnels and shafts are cost-effective solutions for a hydropower project being implemented worldwide. To implement this concept, the ground conditions at area concern should be favorable regarding minimum principal stress magnitude, which higher than hydrostatic water head acting on tunnel periphery. In addition, rock mass relatively unjointed or joints in tight. Among most important issues design is extent hydraulic jacking leakage out during operation. This manuscript first presents fluid flow potential assessment two selected locations headrace Upper Tamakoshi Hydroelectric Project (UTHP) Nepal using UDEC. It noted here that 7960 m long will experience vary from 2.9 to 11.5 bars (0.29–1.15 MPa). supported by sprayed concrete (shotcrete) combination with systematic bolts walls crown. invert few hundred meters downstream end (at surge shaft area) after completion all other works. qualitative carried UDEC indicated considerable built-up joint systems suggesting jacking. was especially case segment (downstream chainage 7100 m) tunnel. further quantitative results estimation Panthi (Panthi KK (2006) Analysis engineering geological uncertainties related tunnelling Himalayan conditions. PhD Thesis, NTNU, Trondheim, Norway;Panthi, Note estimating specific Panthi’s approach, 2010;) approach. an average about 2.5 l/min/m tunnel, may result over 210 l/s evaluation also outer reach (860 segment) seems extremely vulnerable 80 occur only operation plant.