白鹤滩水电站地下洞室群规模巨大,地质条件复杂,地应力高,洞室开挖期间安全风险大,需要监测围岩稳定情况。通过分析左岸地下厂房第Ⅰ至第 Ⅳ 层开挖安全监测资料,揭示围岩变形规律、特性和原因,并给出了为稳定围岩采取的工程措施。成果表明:洞室施工期围岩变形是地质条件、地应力和开挖等因素共同作用的结果;错动带、裂隙和断层等地质构造影响洞段的顶拱围岩变形总量和变形深度均相对较大,一般洞段下游拱脚围岩变形相对大;顶拱中心和上游拱脚围岩变形大部分在深度6.5 m以内,下游拱脚部分桩号深度超过11 m的区域有一定变形,上下游岩台围岩变形深度大于顶拱;支护锚杆应力、锚索荷载在厂房内的空间分布规律和变化规律与围岩变形一致;一般洞段顶拱的锚杆和锚索受力仍有较好的余度,岩台层采取的针对性处理措施有效地提升了开挖成型效果。研究成果可为后续开挖期间围岩稳定的控制提供参考。

The underground powerhouse cavern in Baihetan Hydropower Station is in an extremely grand scale with complex geologic conditions, high initial ground stress, and high safety risks in excavation stage. The rules, characteristics and causes of surrounding rock deformation of left bank underground powerhouse were revealed by analyzing the safety monitoring data of the first to fourth floor excavation. Engineering measures to stablize surrounding rock were introduced. Results suggested that the deformation of surrounding rock during excavation was resulted from the combined actions of geological condition, geostress, and excavation. The total amount and depth of deformation of the crown influenced by geological structure were both large, and the deformation of the arch foot downstream of other tunnels were relatively large. Most of the deformation in the center of the crown and the upstream arch foot did not exceed 6.5 m, while the area beyond 11 m depth of downstream arch foot also witnessed some deformation. The deformation of the upstream and downstream platform was deeper than that of the crown. The spatial distribution and development of bolt stress and anchor bolt stress were consistent with those of surrounding rock deformation. There was still some space for bolt stress and anchor bolt stress in common tunnel sections. The present treatment measures for the platform layer have effectively improved the excavation and forming effect.