三峡库区万州区四层岩危岩带发育特征、稳定性评价及防治对策

三峡库区万州区是危岩灾害集中发育的典型地区，位于主城区的四层岩陡崖带发育众多危岩单体，对下方公路和居民区构成严重威胁。为了有效防治该危岩灾害，首先，基于详细的野外调查和勘查，查明了危岩带发育的工程地质条件和基本特征，危岩体形态可划分为块状、板状和不规则状3种；体积从几十至几千立方米不等；破坏模式可归纳为坠落式和倾倒式2类。通过分析危岩区的地质环境条件，认为多级陡崖带地貌、上硬下软的岩性组合、结构面的组合切割、降雨和地下水作用以及植物根劈作用是导致危岩形成的主要因素。在此基础上，采用赤平投影法对陡崖带宏观稳定性进行了定性分析；进一步地，采用刚体极限平衡法对危岩体在不同工况下的稳定性进行了定量评价。结果显示，陡崖带目前整体处于稳定状态；危岩体在天然状态下多处于基本稳定—稳定状态，然而，在暴雨和地震条件下，危岩体的稳定性显著下降，且地震作用的影响比暴雨更大。最后，根据危岩体的发育特征、失稳模式及现场施工条件，提出了清除危岩、嵌补和支撑岩腔、裂缝灌浆、锚固、被动防护网等防治措施建议。本文研究成果可以为类似的危岩灾害的研究和防治工作提供参考。

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.