Rock Tunneling Applied to Steady Water Resources Supply in Taiwan: Challenges and Examples

Abstract

Increasing soil erosion and slope collapse in some catchment area in Taiwan in the past decade has increased sedimentation rates of reservoirs and reduced their effective capacity, severely affecting the steady water supply. Among multiple measures that have been proposed for stabilizing the water supply, the construction of tunnels for trans-basin diversion and the release of sediment are the most effective and sustainable. Tunneling in a catchment area, even close to a dam, represents serious environmental and engineering risks. This manuscript presents two cases of rock tunneling applied to steady water resources supply. The background of these two projects, relevant geotechnical conditions and tunneling designs are presented. Challenges and some distinctive issues, such as the presence of a high temperature ground, a combustible gas emission ground, and potential instability of rock wedges caused by large underground excavation, are discussed. Associated countermeasures are then presented, associated with a clever design of an elephant-trunk intake pipe to release turbid water from 15 m below tunnel entrance, and related design strategies applied for a huge underground stilling pool and outlet sections. State-of-the-art tunneling through rock and some innovative tunneling technologies are utilized in these two cases.