Abstract: A well-developed karst development area in Qian Nan Prefecture, Guizhou Province was selected as the research background. A total of eight known collapse sites in the study area were investigated and analyzed. By investigating the relationship between the underground dark river and the distribution of karstic rock caves near the collapse sites, the scale of the collapse body, the lithology of the top plate of the caves and the structure of the rock body, etc., we s〖HJ*4/9〗ummarize the development characteristics of the deep karst bedrock collapse and the mechanism of the collapse. The results show that: (1) the deep karst subsidence in the study area occurs mostly in the area of fracture tectonic development, the subsidence area is more developed in the dissolution fissure and subducting cavern, and the subsidence location is affected by the underground dark river and the subsidence scale is controlled by the structural surface; (2) according to the lithology of the cavern roof plate and the structure of the rock body, this kind of subsidence mode can be summarized into the gravity collapse of the crushing type of the karst roof plate and the gravity collapse of the penetration type of the karst roof structural surface; (3) the subsidence mechanism of the deep karst bedrock is summarized as follows. The depth of the subducted cavern determines the depth of collapse, the degree of fragmentation of the rock body and the development of the structural surface of the cavern roof affects the stability of the roof, and the low stability of the cavern roof is easy to induce the karst collapse when the deep-cut dissolution structural surface is developed. Through the study of this kind of collapse, we have a deeper understanding of the development characteristics and collapse mechanism of deep karst collapse, which will provide some reference for the subsequent collapse early warning work.

Key words: Deep Karst, Gravitational Collapse, Collapse Mechanism, Cave Roof, Stability