Numerical calibration of mechanical behaviour of composite shell tunnel linings

•Four-point bending tests were carried out on composite shell lining beam samples.•Strain distribution across composite lining cross-section identified.•Numerical analyses verified the suggested range of interface stiffnesses.•Proposed numerical model was capable of predicting the composite mechanical behavior.•Sensitivity study investigates the impact of interface stiffnesses and position. Composite shell linings consist of primary and secondary sprayed concrete linings separated by a layer of spray-applied waterproofing membrane. In order to design such a lining configuration, a calibrated numerical simulation approach is needed and the impact of interface properties on the composite mechanical behaviour should be understood. A programme of laboratory tests was carried out on beam samples cut from composite shell test panels and subjected to four-point bending under short-term loading. A range of membrane thicknesses and substrate roughness were compared and composite mechanical behaviour quantification methods developed. The behaviour of composite beams was understood and the strain distribution across composite lining cross-section was identified. A numerical model by the finite difference method was then set up for the beams and verified against the test data. With interface stiffnesses obtained from previous element tests, the composite beam model is capable of predicting the strain distribution across the cross-section and real behaviour of composite beam members to within an acceptable level of accuracy taking into account variations arising from workmanship. Sensitivity studies were carried out to understand the impact of interface properties and membrane interface position on the degree of composite action.