Ten years of continuous monitoring in a mining panel

Abstract

The Brooklyn Tunnel is an 8.9 km segment of City Tunnel No. 3, a new water supply pressure tunnel for the City of New York. A 5.8 meter diameter Tunnel Boring Machine recently completed excavation through high grade gneisses and associated intrusives. The project achieved a TBM utilization rate of 32.5%; mechanical downtime totaled 18.5% of available hours. Three factors which affected excavation progress were excessive cutter wear, numerous zones of adverse ground conditions, and pregrouting to avoid heavy inflows on a downhill heading.