Challenges associated with the construction of vertical and inclined shafts in the Himalayan Region

Abstract

In the Nepal Himalayas, hydropower projects having an installed capacity of over 10MW usually consist of underground waterways. Most of these underground waterways consist of vertical or inclined pressure shafts, which are part of the headrace system of a hydropower project. Excavation of these shafts requires special techniques, and the performance is dependent on the quality of rock mass. Therefore, the selection of an efficient construction method for shaft excavation is most challenging work. This manuscript evaluates the challenges associated with the construction of shafts for three hydropower projects in the Nepal Himalayas. The achieved construction progress of each method is compared with actual geological conditions. It is concluded that the major challenges associated with the excavation of pressure shafts through the Himalayan rock mass conditions are frequent overbreak, water inflow, debris flow, difficulties in surveying and control of shaft alignment, ventilation, poor visibility, and pilot hole deviation.