Interface parameters of composite sprayed concrete linings in soft ground with spray-applied waterproofing

•A composite shell lining interface is subjected to compression, tension or shear.•Interface parameters are insensitive to substrate roughness and membrane thickness.•Long-term relaxation ratios under the different loadings are quantified.•Interface tensile strength is sufficient to prevent the membrane from debonding.•Shear stiffness is sufficient to maintain composite action in the long term.