Use of Ground Freezing for Connecting Two Tunnel Boring Machine- Driven Tunnels 300 Feet Underground

摘要

With half of the 6,100-m- (20,000-ft)-long Brightwater Conveyance System Tunnel 3 completedrnin glacial and non-glacial deposits, cutterhead damage to the tunnel boring machine (TBM) was detected thatrnled to it being abandoned. The TBM position—about 100 m (300 ft) underground with more than 5 bar ofrnhydrostatic pressure—meant it was not possible to access it from the ground surface. A plan was developedrnand successfully implemented to complete the remaining tunnel section with a smaller-diameter TBM miningrnfrom the opposite direction into the disabled, larger-diameter TBM shield. At the connection point, the groundrnwas frozen around the disabled TBM using freeze pipes drilled from the ground surface, supplemented byrnfreeze pipes drilled from inside the TBM. This freezing stabilized the soils at the tunnel face and cut offrngroundwater, which allowed workers to access the cutterhead under atmospheric conditions, dismantle thernTBM and completely empty the shield. This paper describes the design considerations and implementation ofrnground freezing work, TBM docking operations and construction of the tunnel connection.