丰宁抽水蓄能电站地下厂房洞室群的施工期围岩变形具有量值大、时效特征明显、不同深度围岩均可能发生变形的特点。为研究该地下厂房围岩变形时效特征,基于工程地质条件和监测数据,开展围岩变形机制研究。分析结果表明:地下厂房围岩变形的分布特征和时效特性,既与围岩在开挖卸荷后所出现的岩体质量下降、围岩强度减小、岩体蚀变现象有关,也与围岩内存在节理裂隙或断层等不连续地质结构在开挖卸荷作用下易发生张开或错动有关。采用由伯格斯流变模型与带拉伸截止限的摩尔-库伦塑性屈服准则组合而成的复合黏弹塑性模型,进行围岩流变力学参数反演,获得了与监测值吻合较好的围岩变形和变形时程曲线计算结果。根据洞室群围岩开挖支护稳定性分析结果,可知截至主厂房第V层开挖支护完毕,洞周围岩局部变形和塑性区深度均较大,且塑性区贯穿主厂房和主变室洞间岩柱,围岩稳定性总体较差。因此,主厂房在第V层开挖完毕后暂停继续下挖,专门进行洞室群的系统性加强支护是必要的。

The surrounding rock mass of the underground powerhouse of Fengning pumped storage power station, in its construction period, exhibits various characteristics including large deformation magnitude, significant time effect, and occurrence of deformation at any depth of rock mass. The mechanism of rock mass deformation is analyzed based on geological conditions and monitoring data to study the distribution of rock mass deformation and its time effect characteristic. Results reveal that the deformation mechanism is, on one hand, related to the degradation of rock mass quality, reduction of rock mass strength, and rock mass alternation, and on the other hand, related to the excavation unloading induced open and dislocation of discontinuities, such as joints, fractures and faults that are distributed in rock mass. The Burgers rheological model combining Mohr-Coulomb yield criterion considering tensile limit is adopted as a compound visco-elastoplatic model to conduct back analysis of mechanical parameters of surrounding rock masses. The obtained deformation magnitudes and their time curves are in good agreement with monitored data. According to numerical calculation results, as of the completion of the fifth layer of main powerhouse construction, the rock mass deformation and plastic zone are both large. As the plastic zone runs through the rock mass pillar between the main powerhouse and main transformer hall, the rock mass stability is considered not favorable. Thus, it is necessary to suspend the subsequent construction after the fifth layer construction of main powerhouse is finished. A systematic reinforcement of anchor support towards the whole underground powerhouse is also required.