Design of Tunnel Support System, Shotcrete Versus Rock Bolts in Middle Modi Hydroelectric Project (MMoHP)

Middle Modi Hydropower Project (MMoHP) is located in Himalayan geology with tectonically youngest geological formations in Nepal and seems challenging for the construction of underground structure like tunnels. Although tunnel support system designs are explained in literature and previous studies, the limitations are mostly attributable to the specific geological conditions and conventional methods of shotcrete and rock bolts, which created the necessity of this research. This research aimed to assess the benefits of the shotcrete tunnel lining method over the other conventional methods in terms of time and economy by conducting the empirical, numerical modeling method. The parameters from rock support system using rock tunneling quality index (Q-value) were used in numerical analysis for conventional rock bolts and shotcrete versus steel fiber reinforced shotcrete (SFRS) support system which was performed by Phase² Software in two chainages 1 + 000 m and 2 + 400 m. The maximum displacement around tunnel contour was found less than 3 mm in first section and 50 mm in second section. Furthermore, the change in thickness of the shotcrete in case of shotcrete and rock bolts and in case of shotcrete only was found 150 mm and 200 mm for first and second sections, respectively. After economic analysis, this study concludes that steel fiber reinforced shotcrete (SFRS) will be more cost- and time-effective than conventional wire mesh shotcrete and rock bolts.