Determination of the stress-strain demand curve of the sprayed waterproofing membrane interface in composite SCL tunnels

•A conceptual framework is established for the membrane states.•These states start from the construction stage and over the whole design life.•These states can be captured in demand curves through numerical modelling.•The range of water pressure application positions can be bounded by demand curves.•The concept of capacity envelopes and demand curves for the membrane are introduced.