Interface parameters of composite sprayed concrete linings in soft ground with spray-applied waterproofing: Fid-Bau Portal

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

Su, Jiang / Bloodworth, Alan

Highlights • 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.

Abstract The presence of a spray-applied waterproofing membrane between the primary and secondary lining layers is important to the behaviour of a composite sprayed concrete lined (SCL) tunnel in soft ground. In order to confirm the feasibility of the composite shell lining concept, the structural adequacy of the concrete-membrane interfaces under the effects experienced in a typical tunnel needs to be investigated. 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.