Seismic responses of cross-passage tunnel in blasting damage condition

ObjectiveThe blasting excavation of transverse passages in urban tunnel expansion projects often leads to performance degradation of linings in adjacent existing tunnels. To clarify the intrinsic coupling mechanism between initial blasting-induced damage and seismic dynamic response, the seismic response characteristics and vulnerable zones of tunnel linings in different degradation states are investigated.MethodBased on wave propagation theory, a time-domain analysis model for 3D planar SV-wave incidence was developed by incorporating viscoelastic artificial boundaries and an equivalent seismic load input scheme. The method was implemented on ABAQUS finite element platform through FORTRAN subroutine development, and its effectiveness was verified using a half-space benchmark model. Furthermore, relying on an actual urban tunnel transverse-passage excavation project, a three-dimensional dynamic coupling numerical model of tunnel structures considering different degradation coefficients was established. The seismic dynamic responses of tunnels subjected to initial blasting damage were systematically analysed.ResultUnder horizontal seismic action, the peak acceleration at tunnel invert exceeds that at crown, showing the trend of initially gradual then rapid increasing varying with degradation coefficient growing. The tunnel crown at connections represents a stress concentration zone. The vertical relative displacements significantly exceed horizontal ones, exhibiting notable flattening deformation. The relative displacement of existing linings shows a nonlinear positive correlation with degradation coefficient, while the stress displays a nonlinear negative correlation. The blasting-induced degradation significantly amplifies seismic response. When the degradation coefficient exceeds 0.2, both displacement and stress responses increase abruptly by over 10%, indicating a marked decline in structural safety.ConclusionThe degradation coefficient of 0.2 can be identified as an early-warning threshold for seismic performance deterioration of existing tunnel linings after blasting disturbance. The findings provide a theoretical basis for performance degradation warning and preventive strengthening of cross-passage tunnel in similar urban tunnel expansion projects.