某水电站巨型地下厂房第一层开挖施工过程中 0+125 m 至 0+147 m 段发生塌方，塌方总规 5 000 m3 ，塌腔呈不规则的葫芦状。结合施工期的监测成果和现场实际情况，从工程地质、爆破震动、开挖卸荷、支护措施以及应力集中等 5 方面 , 阐述了塌方形成机理，得出了如下结论：地下厂房塌方形成的根本原因是存在β 80 岩脉断层；直接原因是β 80 岩脉断层段支护措施不当，未能有效限制岩脉断层带由于爆破开挖引起的较大变形。因此，针对地下洞室爆破开挖后暴露的地质薄弱带，及时采取适当的支护和加固措施，加强围岩变形观测，是控制和避免塌方的有效手段

During the first stage excavation of the giant underground powerhouse, a collapse occurred between 0 +125-0 +147 m with the total collapse volume of 5 000 m3 and the cavity appeared like an irregular gourd shape. In accordance with monitoring result of the construction period, the formation mechanism of collapse is expounded from the five aspects of engineering geology, blasting vibration, excavation unloading, support measures as well as stress concentration. It is concluded that the primary cause of collapse formation in the underground powerhouse is the existence of vein fault β 80, while the direct cause is that deformation of vein fault β 80 caused by excavation and blasting vibration cannot be effectively controlled by support measures. So appropriate supports and reinforcement measures should be taken in the exposed surface of excavation in the zone of fracture and surrounding rock deformation monitoring should be strengthened, which is the effective means to prevent collapse occurrence.