Wastewater flow transfer tunnel: design and construction

This paper discusses the design and construction of a 10·5 km long, segmentally lined, flow transfer tunnel. It covers the detailed lining and shaft designs, selection criteria for the tunnelling machines, shaft and tunnel construction methods, and specialist ground treatment. The paper discusses several construction problems encountered with shaft sinking and tunnelling, and describes how these were resolved. Particular note is made of caisson sinking of shafts and the design of the tunnel entry and exit portal eyes. Jet grouting in the varying ground strata around these portals and on other areas of the contract is considered.