Abstract: To investigate the mechanisms of failure and instability in steep karst slopes with deep and large fissures due to mining activities, a comprehensive review of typical rock collapse and landslide cases in karst mountains with such fissures in southwestern China over the past 50 years was first conducted, and the basic characteristics of these collapses and landslides were analyzed. Subsequently, taking the collapse at Yaoyanjiao in Houchang Town as a case study and based on extensive field investigations, a thorough examination was carried out using similar physical model tests and theoretical analysis to explore the impact of underground mining on the deformation and failure of the steep karst slope with deep and large fissures. The controlling effect of these fissures on the mining-induced slope was discussed. The mechanism of slope collapse and instability was elucidated, and the stability variation of slope before and after collapse were obtained. Finally, the failure and instability modes of steep karst slopes with deep and large fissures under various geological conditions due to mining activities were discussed, revealing the formation mechanisms of different collapse and landslide modes. The results indicate that the deformation and failure of the slope adjust continuously with the progression of mining. Initially, the slope behind the deep and large fissure experiences settlement and outward deformation, ultimately transitioning into a failure mode of “cantilever collapse”. The dangerous rock mass undergoes initial backward inclination deformation followed by forward toppling as mining progresses. The deep and large fissures exert a segmentation effect on the deformation of the mining-disturbed slope, which is correlated with the mining process. Underground mining exerts a decisive influence on the deformation and failure of steep karst slopes with deep and large fissures. Although there are certain similarities in the mechanical responses of different mountains to underground mining, the modes and mechanisms of ultimate collapse of the slopes exhibit significant differences under varying engineering geological conditions.

Key words: steep karst mountain, deep and large fissure, underground mining, deformation failure, instability mode