Dynamic analysis and protective structure optimization for clustered rockfall hazards triggered by the 2017 Jiuzhaigou earthquake: insights from 3D numerical modeling

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Introduction Clustered rockfall hazards triggered by the 8 August 2017 Jiuzhaigou earthquake pose serious risks to infrastructure in mountainous areas. This study investigates the dynamic characteristics of clustered rockfalls and evaluates mitigation measures in the Zhongjijie Lake area. Methods Field surveys were conducted to assess damage to existing protective structures. A high-resolution three-dimensional model of the affected slope was developed using unmanned aerial vehicle (UAV)-based photogrammetry. Rockfall trajectories were back-analyzed based on the observed geometry and sizes of fallen rock masses. The resulting impact locations and velocities were then used to construct an impact-coupled discrete element model incorporating rigid retaining walls. Comparative simulations were performed for mortar rubble retaining walls with and without an expanded polystyrene (EPS) buffer layer. Results Field observations showed that rockfalls caused substantial damage to both active and passive flexible protective nets, whereas rigid retaining walls at the slope toe exhibited robust protective performance. The simulations indicated that incorporating EPS substantially reduced stress concentrations and microcrack propagation in the masonry structure. An EPS thickness of 0.3 m reduced frictional energy transfer within the retaining wall by a factor of 4.12. Discussion Combining mortar rubble retaining walls with an EPS buffer layer can improve impact resistance and energy dissipation, providing an effective mitigation strategy for clustered rockfall hazards in high-risk mountainous terrain.

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