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

This paper presents a series of laboratory tests on samples cut from composite sprayed concrete panels, to which uniaxial compression, direct tension and direct shear loadings are applied over both short- and long-term timeframes under conditions of ambient atmospheric humidity. Test results show that the interfaces are capable of resisting significant compression, tension and shear in both short- and long-term. Failures under these actions should not occur in a typical shallow SCL tunnel, and a degree of composite action between primary and secondary layers should be expected. Influence of substrate roughness and membrane thickness on the measured interface properties has been quantified. Overall, this investigation confirms the existence of composite action for composite sprayed concrete linings in soft ground, and provides parameters based on test results for further research and design.