Seismic response study of shield tunnel with lateral karst cavity under SV waves

Abstract

This paper investigates the seismic effects of karst cavity size and span on the shield tunnel subjected SV waves, using the case project of Dalian Metro Line 5. The viscous spring artificial boundaries are employed for the seismic input, which is validated to assure accuracy. The shield tunnel is simplified according to the method of the equivalent bending stiffness model. The deformation and stress distribution are analyzed to investigate the dynamic response of the shield tunnel under SV waves at different angles. The tunnel damage state is evaluated by the criterion proposed by authors in previous research. The results show that a larger cavity size can lead to more deformation in the tunnel. There are significant differences in the spatial distribution of deformation and stress affected by the incident angle. As the cavity size increases, the stress near the cavity decreases significantly. Only the cavity size is greater than or equal to 0.8D (D is the tunnel’s diameter), there are damage concentration areas on the bottom, and the damage area shifts towards to circumferential direction. The deformation and stress distribution are highly affected as the span increases in the Z direction, followed by the Y direction, and almost no effect in the X direction. The damage area increases as the increase of span in three directions. There are damage concentration areas of the bottom only as the span is 1.5D in the Z direction. Compared with the effect of cavity size, the results indicate that the damage concentration is not solely related to cavity span in one single direction.