以大岗山水电站地下厂房在第一层开挖施工过程中的顶拱塌方及其支护加固为研究实例，在塌方区地质调查基础上，通过有限差分程序FLAC  3D建立数值分析模型，研究了塌方区的支护加固效果及后续开挖对塌方区稳定性的影响。研究表明：塌方后顶拱碎石区变形较大，而其它关键部位位移变化不大，变形增加均在3mm以内，说明施加支护对滑体周边区域变形起到了较好的控制作用；随着主厂房继续开挖，围岩应力卸荷调整，锚索、拱撑等与围岩相互作用，滑体附近岩体应力分布趋向均匀，拱顶拉应力区基本消失；锚索内力增大并逐步向深部传递，说明锚索在后续开挖中有效发挥了支护力，对于塌方区的稳定起到重要作用。

Based on geological investigation, a numerical calculation model was established by FLAC  3D to simulate the collapse and supporting consolidation during the first-stage excavation of underground powerhouse of the Dagangshan hydropower station. The consolidation effect and the influence of subsequent excavation after collapse on the stability of collapsed area were studied. The results showed that apart from larger  deformation  in the crushed stone zone, the deformation increase in other crucial locations was within 3mm after the top arch was reinforced by cable and steel arch. The results indicated that the consolidation effect was quite good； and as the powerhouse was excavated, the rockmass stress around collapse zone tended to be even due to the stress adjustment and the interaction among cable, arch and surrounding rock； the tensile stress of collapse zone rock almost disappeared； the anchor force increased and extended deeper gradually, indicating that the anchor worked effectively.