Influence of Mainshock-Aftershock Sequence on Nonlinear Seismic Response of Hollow Gravity Dam

[Objective] To investigate the influence of mainshock-aftershock sequences on seismic performance of hollow gravity dams, the nonlinear seismic response of one overflow dam section in a hollow gravity dam in China is investigated. [Methods] Real mainshock and aftershock records were selected from the PEER (Pacific Earthquake Engineering Research Center) earthquake database. Three mainshock-aftershock sequences, Mammoth Lakes, Chalfant Valley, and Whittier Narrows, were constructed based on aftershock decay characteristics. Taking one overflow dam section of a hollow gravity dam in China as the research object, the 3D finite element model of the dam-foundation system of the overflow dam section was built. The concrete damaged plasticity model was adopted to simulate the nonlinear characteristics of the concrete material of the dam body. The massless foundation was used to simulate the dynamic interaction between the structure and the foundation. The hydrodynamic pressure of the reservoir was simulated by the added mass method. The influence of the mainshock-aftershock sequences on the nonlinear seismic response of the hollow gravity dam was analyzed based on the development of cumulative macroscopic failure areas, the residual deformation of the dam crest, and the cumulative damage dissipation energy. [Results] (1) The failure area of the hollow gravity dam caused by aftershocks usually continued to expand along the failure areas caused by the mainshocks. The aftershocks significantly increased the range and depth of the failure area caused by the mainshocks. In some areas, such as the dam heel and the reverse arc area, when the damage caused by the mainshock was relatively deep, aftershocks could directly lead to a through-going failure of the dam body. (2) Aftershocks could cause a significant increase in the residual deformation at the dam crest and the damage dissipation energy of the dam body. The residual deformations caused by the three mainshocks were 2.13, 2.83,2.12 cm, respectively. When the aftershock coefficient was 0.852 6, the proportion of residual deformation caused by aftershocks was 24.2%, 24.1%, and 26.4%, respectively. The damage dissipation energy caused by the three mainshocks was 131, 121,108 kJ, respectively. When the aftershock coefficient was 0.852 6, the proportion of the dam damage dissipation energy caused by the three aftershocks was 38.8%, 49.6%, and 47.1%, respectively. (3) When the aftershock coefficient was small, it also significantly increased the distribution of failure areas in the dam body. In some regions, non-through failure caused by the mainshock could further develop into through-going failure under aftershocks. When the aftershock coefficient was 0.6, the proportion of residual deformation at the dam crest caused by three aftershocks was 18.4%, 18.2%, and 19.4%, respectively. The proportion of the damage dissipation energy caused by the three aftershocks was 29.9%, 40.1%, and 37.5%, respectively. [Conclusion] The innovation of this paper lies primarily in revealing the influence of mainshock-aftershock sequences on the nonlinear seismic response of the hollow gravity dam. The results indicate that the failure areas caused by aftershocks usually continue to expand along the failure areas caused by the mainshocks. The aftershocks may significantly increase the range and depth of the failure areas caused by the mainshocks. The aftershocks may cause a significant increase in the residual deformation at the dam crest and the damage dissipation energy of the dam body. In the seismic safety evaluation of the hollow gravity dam exposed to earthquake hazards, the influence of aftershocks is non-negligible.