Overtopping Failure of Moraine Dams under Action of Earthquake-Induced Resonant Water Surges

Shaking table model experiments were designed to study the overtopping failure mechanism of moraine dams under action of earthquake-induced resonant water surges (ERWSs). Firstly, movements of earthquake-triggered surges under resonant and non-resonant conditions were compared to examine the main influencing factors of maximum height of ERWSs, and a prediction equation for the maximum height was proposed through dimensional analysis. Then, based on the critical water head condition for coarse particle initiation and the critical water volume condition for sediment transportation in dam break, critical conditions of overtopping failure for barrier dams under water surge actions were established and a risk assessment procedure was developed. Finally, taking the 34 small-scale moraine-dammed lakes located in the Parlung Zangbo River basin as examples, the operation of the proposed procedure was demonstrated. Results show that compared with non-resonant surges, ERWSs have greater amplitudes and a much slower process of attenuation with time, and a steady state with continuous large-amplitude wave motion exists in the time history of the resonant surge. When the seismic resonance effect is considered, the number of dangerous moraine-dammed lakes in the Parlung Zangbo River basin increases from 3 to 11, and the distribution extends to the areas with smaller peak ground acceleration (PGA). The results provide a scientific basis for seismic risk assessment of barrier lakes along the Sichuan-Tibet Railway.