AHP-based Assessment Method for Deterioration-Induced Collapse of Rock Mass in the Hydro-Fluctuation Belt

After the impoundment and operation of the Three Gorges Project, a water-level fluctuation zone with a vertical height of 30 m has formed in the reservoir area. Under the long-term effects of wetting–drying cycles, dissolution and suffosion, and reservoir water dynamics, rock mass deterioration in this zone has become increasingly prominent. The resulting water-related perilous rock collapse hazards are characterized by high concealment, strong abruptness, and significant disaster risk. However, quantitative risk assessment methods targeting such hazards are still lacking. Taking typical water-related perilous rocks in the Three Gorges Reservoir area as research objects, this study reveals the macroscopic characteristics and microscopic mechanisms of rock mass deterioration in the water-level fluctuation zone through field investigations and indoor physicochemical tests. Using the analytic hierarchy process (AHP), a risk assessment indicator system for collapse hazards induced by rock mass deterioration in the fluctuation zone was constructed, comprising 3 first-level indicators and 8 second-level indicators. The weights of the indicators were determined, and a weighted-sum model for calculating the total risk score was established, classifying the disaster risk into four levels: low, medium, high, and extremely high. A visual risk assessment system was developed based on MATLAB GUI. The W5 perilous rock mass at Lingzhifeng in Chongqing was taken as a case study for validation. The results show that under unfavorable conditions, its total risk score is 6.332, corresponding to a medium risk level, which is basically consistent with the conclusions of field investigations. The assessment system and method established in this study exhibit good rationality and practicability and can provide a scientific basis and technical support for the risk management and engineering control of water-related perilous rock collapse disasters in the Three Gorges Reservoir area.