ABSTRACT
Groundwater pressure is the main cause of debonding (i.e. tensile failure) of the sprayed waterproofing membrane interface within composite sprayed concrete lined (SCL) tunnels. The debonding could lead to the groundwater pressure being resisted by the thin secondary lining alone, causing concerns about its stability. Therefore, it is critical to understand the stress status and potential failure mechanisms of the sprayed membrane interface and the practical implications of membrane testing methodology. The paper first reviews the status of the composite SCL research and identifies the most critical issue that prevents it from wider application. It then presents a conceptual relationship between the possible groundwater pressure application locations and the stress state and hence potential failure mechanism of the membrane interface in composite SCL tunnels. The current membrane interface tensile strength testing methodology is then reviewed. Suggestions are made for the improvement of the testing methodology.
