Integrated geophysical and computational modeling of hydromechanical mechanisms of underground debris flows in mining region

• The air-ground transient electromagnetic method-based the spatial distribution characteristics of underground debris flow migration area were revealed. • The coupled computational fluid dynamics–discrete element method-based the hydraulic erosion mechanisms during the migration of underground debris flow and dynamic response mechanisms were explored. Underground debris flows, arising from the complex interplay of anthropogenic activities and rainfall-induced hydromechanical processes, present significant geotechnical hazards that remain poorly understood due to their hidden nature and dynamic multiphase triggers. Focusing on underground debris flow in a mining area in Southwest China, this study advances an integrated framework combining air-ground transient electromagnetic method (AGTEM) and computational fluid dynamics coupled with the discrete element method (CFD–DEM), revealing the migration mechanism in which microscale multiphase hydraulic erosion drives the macroscopic initiation of underground debris flow. Key findings include: (1) The identification of three transport phases (rapid erosion, slow erosion, and stabilization) provides actionable thresholds for monitoring and mitigation. (2) The coupled feedback between hydraulic conductivity anisotropy and the formation of preferential flow is the primary driver of large-scale debris transportation. (3) Linking mining-induced seismic energy to vibration-induced liquefaction via DEM simulations offers a physics-based explanation for flow mobilization triggers. The integrated geophysical-numerical framework offers new capabilities for predicting initiation thresholds and developing physics-based mitigation strategies in mining-affected terrains.