Nonlinear dynamic analysis and damage evaluation of hydraulic arched tunnels under mainshock-aftershock ground motion sequences

The significant life engineering failure and financial toll caused by mainshock-aftershock (MSAS) ground motion sequences have highlighted the importance of focusing on aftershocks. The current seismic design of hydraulic arched tunnels generally involves a dynamic analysis that assumes that a single seismic excitation or multiple single seismic excitations are applied. However, this assumption may underestimate the seismic response of hydraulic arched tunnels. The focus of this study is to evaluate the effect of both the mainshock excitation-induced nonlinear response and the MSAS excitation-induced nonlinear response of hydraulic arched tunnels. For this purpose, a numerical model is built in the commercial software ABAQUS, and it considers the fluidstructure-rock interaction system. Twenty-one as-recorded MSAS ground motion sequences are selected, and the seismic wave input method is verified before a nonlinear dynamic analysis is conducted. According to the damage patterns of tunnels under Wenchuan seismic excitation, the lining local damage index (LLDI) and the lining global damage index (LGDI) are established to assess the effect of single mainshock excitations and MSAS excitations on hydraulic arched tunnels. The results reveal that MSAS excitations can cause relatively severe cumulative damage and have a negative impact on the nonlinear dynamic response of the hydraulic arched tunnel compared to single mainshock excitations. Moreover, the aftershocks not only lead to an increase in the LGDI of the hydraulic arched tunnel at the end of the MSAS excitations but also enhance the LLDI of the arch section and sidewall section. In contrast, the aftershocks induce no significant change in the LLDI of the bottom section of the hydraulic arched tunnel. Thus, MSAS excitations should be considered in the seismic design of hydraulic arched tunnels.