As a part of a much larger CSO program the design of the 23 ft (7m) ID segmental lining forrnthe Blue Plains Tunnel offered significant benefits over traditional two pass systems. However, careful designrnwas required to achieve the 100 year design life and provide structural resistance to an internal pressure thatrnwas higher than the external pressures on the lining. This paper describes how these and a number of otherrnrequirements were incorporated into the design to provide a ring that performs robustly for functional, costrnand constructability criteria. Finally, comments are made on the performance of the ring in the tunnel andrnrecommendations made for future designs.
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