ABSTRACT
Cross passage design is a specialised subject with limited published guidance. This paper describes some of the key risks in cross passage design, particularly for large TBMs. Spaceproofing and geometrical design is important but poorly recognised in literature, with complications caused by the ring joint locations along the TBM drive. Ground treatment for the segment opening is another key design problem for the cross passage design. Finally, the design of the ring opening to be both safe and economical is a key issue. These issues are discussed with reference to a current large diameter (15.7m) TBM road tunnel in Sydney. This tunnel crosses Sydney Harbour, which is an ancient river, infilled since the ice ages with a deep palaeochannel. The rock is affected by the channel with the opening of joints by stress relief and by valley bulging. The tunnel encounters a 180m section of soft ground, which is the infilled palaeochannel. The TBM cross passages are in rock, with potential water ingress related to the geological conditions of stress relief and valley bulging. The opening rings of the TBM tunnel are designed to use cored shear keys to transfer the load around the segment opening. The detail includes a cast-in bond-breaker to minimise damage. The collar structure of the cross passage is described with a solution adopted to maximise the opening width.
