Simulating composite behaviour in SCL tunnels with sprayed waterproofing membrane interface: A state-of-the-art review

•Sprayed waterproofing enables tension and shear transfer between lining layers.•load transfer can give efficiency gains in lining design, but not in all cases.•A guaranteed benefit of interface tensile bond is sharing of groundwater loading.•Composite action can induce tension in secondary from bending, reducing its capacity.•Concern about water saturation of membrane can be addressed by limiting water head.