Tunnel Stabilization: A Case Study of Effective Grouting and Support Measures in Upper Sanigad Hydroelectric Project, Bajhang, Nepal

Abstract

This case study presents a comprehensive overview of the small size tunnel stabilization and excavation efforts undertaken in the Upper Sanigad Hydroelectric Project (USHEP), located in the Kalanga Basin, Bajhang, Nepal. The project site is situated in the Lesser Himalaya geological unit, Galyang Formation of Midland group, by complex geology comprising meta-sedimentary and carbonate rocks. The tunnel excavation faced significant ground stability challenges due to the weak and fractured nature of the rock masses, high tectonic stress, and significant water pressure.

The project team employed a combination of grouting, debris removal, and support measures, including forepoling, rib installation, and sprayed concrete. The treatment process, which spanned approximately three and a half months, successfully stabilized the tunnel and allowed for safe excavation. A total of 1031 bags of cement were used in the two stages of grouting, and 2078 cubic meters of debris were removed from the tunnel.

The project's success demonstrates the effectiveness of a well-planned and executed stabilization and excavation strategy in overcoming complex geotechnical challenges in the Himalayan region. The case study highlights the importance of careful planning, precise execution, and adaptability in navigating uncertain geological conditions. The findings and lessons learned from this project can be applied to similar tunnel stabilization and excavation projects in the Himalayas, providing valuable insights for geologists, engineers, contractors, and project managers.