The Three Rivers Protection and Overflow Reduction Tunnel (3RPORT)-Design Challenges of the Launching of Pressurized Slurry TBM

摘要

Depending on the hydro-geological conditions and the overall project constraints, a tunnel boring machine (TBM) may be launched under high support pressure. The "pressurized" launching of a TBM represents a major design challenge particularly when the TBM is launched from a starter tunnel. The present paper focuses on the launching of the slurry TBM, named "MamaJo," of the 3RPORT tunnel. The tunnel is part of the Long-Term Control Plan of the City of Fort Wayne (Indiana, USA) having the main goal to reduce the discharge of untreated Combined Sewer Overflows (CSOs) and to improve the water quality in Fort Wayne's CSO-impacted streams. The tunnel will have a length of about 7.5 km, an internal diameter of 4.87 m and will be excavated at a maximum depth of 60 m. Carbonate rocks are expected over the entire alignment. Due to the high rock mass permeability and high in-situ hydrostatic pressure at the tunnel elevation, the launching of the TBM has been designed taking into account a support pressure up to 6.5 bar. The paper presents the main geotechnical hazards for all launching stages as well as their impact on the design solutions. Finally, it summarizes the lesson-learned after the successful launch of the slurry TBM in April 2019. Particular attention is paid on the design of the launching chamber (incl. concrete bulkhead as well on the selection of the required TBM parameters.