Formation conditions and prevention-control technologies of slope-type debris flows in mountainous areas

Mountain slope-type debris flows are characterized by high suddenness, no distinct transport zone, and rapid hazard initiation. Understanding their formation conditions and developing control technologies are key to disaster prevention and mitigation. Based on field surveys, laboratory tests, and long-term monitoring data from a typical catchment in Southwest China, this study systematically analyzes the coupling mechanism of the three controlling factors, topography, source material, and water trigger, and proposes quantitative thresholds for formation conditions. The results show that: topographically, slope gradients of 20°-40° with concentrated relief and no independent transport zone facilitate rapid potential energy conversion; regarding source material, loose deposits with a thickness of no less than 0.5 m, natural density of 1.65-1.85 g/cm³, internal friction angle of 25°-32°, cohesion of 5-15 kPa are required, and the underlying bedrock with poor permeability tends to form a perched water zone; hydrologically, short-duration heavy rainfall serves as the direct trigger. On this basis, a coupled early warning model integrating antecedent rainfall and short-duration heavy rainfall is constructed, and three warning levels (blue, yellow, and red) are defined according to the model output. A comprehensive engineering control strategy of "source reduction, path regulation, and terminal protection" was designed, including gravity check dams in the source area, as well as drainage ditches and vegetation reinforcement. Application results show that after treatment, the average monthly displacement at eight surface displacement monitoring points decreased from 6.8 mm to 1.2 mm (an 82% reduction); the maximum cumulative displacement dropped from 87 mm to 18 mm, (a 79% reduction); the mean absolute deviation of the rainfall monitoring system is 0.11 mm; the check dam retains 960 m³ of solid material annually; and the early warning system provides an average lead time of 42 minutes. This technology system integrates a closed-loop disaster prevention process of monitoring, early warning, and emergency response, providing a quantifiable technical reference for the prevention and control of slope-type debris flows in mountainous areas.