Development characteristics, stability evaluation, and preventive measures of the dangerous rock zone at Sicengyan in Wanzhou District of the Three Gorges reservoir area

Wanzhou District in the Three Gorges Reservoir Area is a representative area where dangerous rock disasters develop intensively. Numerous dangerous rocks have been found developing at Sicengyan cliff zone in the main urban area of Wanzhou, which pose a great threat to the roads and residential areas below. To prevent and control the dangerous rock hazards effectively, the engineering geological conditions and development characteristics of the dangerous rock zone are determined through detailed field investigations and explorations. The shapes of the dangerous rocks are divided into three kinds: blocky, platy and irregular, with volumes ranging from dozens to thousands of cubic meters. The failure modes of dangerous rocks are classified into two types: falling mode and toppling mode. By analyzing the geo-environmental conditions of the dangerous rock zone, it is concluded that the main factors leading to the formation of the dangerous rocks are the topography of multi-level cliffs, the combination of upper hard rocks and lower soft rocks, and the rock mass structures formed by the cutting of the structural planes, the action of rainfall and groundwater, and the splitting effect of plant roots. On this basis, the macroscopic stability of the cliff zone has been analyzed qualitatively using stereographic projection technology, and furthermore, the stability of each dangerous rock under different conditions is evaluated quantitatively using the rigid body limit equilibrium method. The results show that the overall cliff zone is currently in a stable state, and the dangerous rocks are mostly in a basically stable to stable state in their natural state. However, the stability of them is likely to decrease significantly under heavy rainfall and earthquake conditions, and the earthquake action exhibits a greater impact than the heavy rainfall on the stability of the dangerous rocks. Finally, according to the development characteristics and instability modes of the dangerous rocks, as well as the construction conditions of the cliff belt, several preventive measures are suggested, such as the removal of the dangerous rocks, patching and supporting of the rock cavities, grouting of fissures, anchorage and passive protection net. This paper could provide a significant reference for research into and efforts to prevent similar dangerous rock hazards.