ABSTRACT

Traditionally, no bond has been assumed across waterproof membranes installed between tunnel primary and secondary linings. Spray-applied membranes offer the opportunity to take into account some bond between the two linings, producing a composite action. The composite action has been verified through a significant laboratory testing programme from recent research from Pillai et.al. (2017). In addition, Jung et.al. (2017) have proposed a design chart for the determination of the secondary lining thickness which will allow designers to reduce the total lining thickness when composite action is considered. This paper presents a microscopic interpretation of the bond interface behaviour in composite lining that will allow further understanding of the mechanism of load transfer between the outer and inner linings, and allows the authors to provide a practical commentary on the application of the bond layer. Also, this paper provides the results of the analytical work done to investigate the effects of membrane thickness, tunnel diameter and shear strength parameters of the interface.