Upper Limit Microtunneling Application to Meet Dam Safety and Operational Longevity

摘要

Gilboa Dam in upstate New York impounds Schoharie Creek, forming Schoharie Reservoir-a part of NYC's water supply system. To ensure the dam's long-term performance and reliability, a Low-Level Outlet (LLO) is being constructed to facilitate reservoir draining to meet conservation releases. It consists of two 9-foot-diameter tunnels (water leg and land leg) totaling 2,160 linear feet, terminating at a new chamber releasing water to the Creek downstream. Excavation is by microtunnel boring machine (MTBM). The land leg tunnel terminates downstream while the water leg tunnel upstream, and penetrates into a coffer dam at the reservoir bottom elevation 977 (-153 feet). This paper presents LLO microtunneling design considerations and construction methods.