乌东德水电站共布置5条导流洞(其中左岸2条，右岸3条)。高、低洞洞身段断面呈城门洞型，断面尺寸分别为12 m ×16 m和16.5 m ×24 m。2012年2月乌东德水电站导流洞开始施工，落雪组因民组极薄层~薄层大理岩化白云岩、层面附绢云母构成的Ⅳ类围岩洞段按5层开挖，在第一层开挖过程中因民组Ⅳ类围岩洞段左顶拱普遍出现塌方，第二层和第三层开挖时，导流洞左右边墙变形位移急剧增大。通过研究导流洞Ⅳ类围岩地质条件及变形失稳模式，分析变形过程与开挖支护的关系。在此基础上优化设计方案，确保了导流洞的安全施工。%Five diversion tunnels, 2 on the left bank and 3 on the right, are built in Wudongde Hydropower Station. In an U-type shape, the profile sizes of the high and low tunnels are 12m × 16m and 16. 5m × 24m respectively. During excavation star-ted at February, 2012, the tunnel sections in the IV surrounding rock composed of Luoxue and Yinmin formations marked by ex-tra-thinly and thinly bedded marble dolomite and sericite on the top of the bed are divided into five layers. The left vault of the sections in the IV surrounding rock composed of Yinmin formation often collapsed during excavation of the first layer. The deform-ation monitoring of the tunnels revealed that deformation displacement of the left and right side walls increased drastically during the excavation of the second and third layers. Through analysis of the geological conditions and the failure modes of the IV sur-rounding rock, the relation between the deformation process and the excavation support, the design scheme is optimized so as to ensure the safe construction of the diversion tunnels.
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