Three‐Dimensional Dynamic Analysis of Debris Flows Over Complex Terrain

Debris flows, characterized by a heterogeneous mixture of solid, liquid, and gas phases, exhibit complex mechanical behavior and pose substantial threats to infrastructure and human lives in mountainous regions. This study presents a novel three‐dimensional material point method (MPM), integrating a geographic information system (GIS) and Perlin noise functions, to model the debris flow over complex terrain as a coupled liquid‐solid system. The digital elevation models in GIS are mapped directly onto the MPM computational domain and preserve realistic terrain features. The irregular rock blocks generated by Perlin noise function in Houdini software are embedded into the source zone of debris flow to explicitly represent fluid‐solid interactions. In addition, to maintain the computational accuracy and efficiency, the sparse paged grid structure (SPGrid) is introduced to provide an efficient computational framework for large‐scale 3D hazard analysis. The proposed MPM framework is validated firstly by comparing numerical results and experimental data from previous studies, including saturated soil leakage, rockslide‐induced wave generation, and debris dam break flow. The dynamic behavior and deposition patterns of debris flows are then analyzed, revealing that these factors are significantly influenced by rock block content and the basal friction coefficient. Results show that the proposed two‐phase two‐point MPM is an effective tool to reproduce the realistic propagation of debris flows and provides a scientific reference for hazard assessment and disaster prevention in debris flow‐prone regions.