The analysis of tunnel seismic fragility serves as the foundation of seismic risk assessment for tunnels in high-intensity zones. The composite lining structure is commonly adopted in tunnels located in high-intensity zones. Most existing seismic fragility analysis methods for tunnels neglect the displacement discontinuities at the interface between the initial primary-secondary lining

particularly in the presence of a waterproofing board. Consequently

direct shear tests were performed on the primary-secondary liner interface incorporating a waterproofing board. A contact model was developed for the interface

along with its corresponding simulation code. Subsequently

the incremental dynamic analysis method was employed to evaluate the seismic fragility of a composite-lined tunnel. The results reveal that shear stress-shear displacement curves can be categorized into four distinct stages: linear growth

nonlinear growth

damage-induced decrease

and friction slip. The waterproofing board decreases the stiffness and strength of the interface. Under normal stress ranging from 0.3 MPa to 2.0 MPa

shear strength increases linearly with normal stress

with a friction angle of 23.7º and cohesion of 0.18 MPa. The waterproofing layer absorbs deformation during earthquakes

acting as a buffer. Compared with the displacement continuity assumption

considering displacement discontinuities at the primary-secondary liner interface increases damage index thresholds across different damage levels. Ignoring the primary-secondary lining interface effect leads to overestimation of tunnel damage states. This study provides a valuable reference for seismic risk assessment of composite-lined tunnels in high-intensity regions.