Design and construction of an egress tunnel beneath a working hospital

This paper discusses the construction and underpinning design of a 24 m long egress tunnel as part of the expansion of an existing hospital in western suburbs of Sydney. The first part of the paper presents the site geology, subsurface conditions and the pre-construction condition of the egress tunnel site. The next part of the paper presents the construction methodologies that were considered and explains the basis for selecting a two heading approach. The final part of the paper details the two designs that were adopted for the underpinning works. The paper demonstrates the value of close collaboration between the designers and constructors which enabled the tunnel to be constructed without disruption to the hospital’s daily operation.