Comparative modelling of retrogressive landslide runout: 2D and 3D random large-deformation analyses using coupled Eulerian-Lagrangian method

Abstract

Retrogressive landslides in sensitive clays pose significant risks to nearby infrastructure, as natural toe erosion or localized disturbances can trigger progressive block failures. While prior studies have largely relied on two-dimensional (2D) large-deformation analyses, such models overlook key three-dimensional (3D) failure mechanisms and variability effects. This study develops a 3D probabilistic framework by integrating the Coupled Eulerian-Lagrangian (CEL) method with random field theory to simulate retrogressive landslides in spatially variable clay. Using Monte Carlo simulations, we compare 2D and 3D random large-deformation models to evaluate failure modes, runout distances, sliding velocities, and influence zones. The 3D analyses captured more complex failure modes-such as lateral retrogression and asynchronous block mobilization across slope width. Additionally, the 3D analyses predict longer mean runout distances (13.76 vs. 11.92 m), wider mean influence distance (11.35 vs. 8.73 m), and higher mean sliding velocities (4.66 vs. 3.94 m/s) than their 2D counterparts. Moreover, 3D models exhibit lower coefficients of variation (e.g., 0.10 for runout distance) due to spatial averaging across slope width. Probabilistic hazard assessment shows that 2D models significantly underpredict near-field failure probabilities (e.g., 48.8% vs. 89.9% at 12 m from the slope toe). These findings highlight the limitations of 2D analyses and the importance of multi-directional spatial variability for robust geohazard assessments. The proposed 3D framework enables more realistic prediction of landslide mobility and supports the design of safer, risk-informed infrastructure.

Keywords

Retrogressive landslide / Coupled Eulerian-Lagrangian approach / Spatial variability / Runout dynamics / Progressive failure / Hazard assessment

Acknowledgments

This research is supported by the National Key Research and Development Program of China (No. 2024YFC2815400), the Euro-pean Commission (Nos. HORIZON MSCA-2024-PF-01 and 101200637), the Opening Fund of the State Key Laboratory of Water Resources Engineering and Management at Wuhan Univer-sity (No. 2024SGG07), the Shandong Provincial Natural Science Foundation (No. ZR2025MS647), and the Sand Hazards and Oppor- tunities for Resilience, Energy, and Sustainability (SHORES) Center, funded by Tamkeen under the NYUAD Research Institute Award CG013.

0 Supplementary material

Supplementary material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.ijmst.2025.10.002.

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