Abstract: There is along low-angle fauh extending in the dam foundation from BL51 to BL53 in Yunfeng dam，and it is unfavorable for stability against sliding. Various of calculated results show that if the lateral shear strength of rock is not considered, the coefficients of sliding resistance for BL51,BL52 would not meet the requirement of specification, whereas, if advantageous factors concerned such as lateral shear of rock are considered, it would meet requirements. Observational results during many years have shown that the deformation changes within normal confines, uplift pressure in the dam foundation is pretty lower, seepage in dam foundation is not obvious, the dam operates in normal condition. The lateral shear of rock has an impact on the stability against sliding for BL51, BL52 somewhat, but the impact has considerable uncertainties，additionally scourholes downstream is approaching the dam toe, no support for the end rock of BL51, BL52, thus, some reinforcement measure steps should be taken necessarily.

摘要： 云峰大坝50号～53号坝段基础存在缓倾角断层，对抗滑稳定不利。各种方法计算结果表明，不考虑侧向岩石抗剪，51号、52号坝段抗滑稳定安全系数不满足规范要求；考虑侧向岩石抗剪等有利因素，可满足要求。多年观测表明，变形在正常范围内，坝基扬压力较小，漏水量也不突出，大坝工作正常。侧向岩石抗剪等对51号、52号坝段抗滑稳定有一定作用，但不确定性较大，加上下游冲刷坑已接近坝趾，无尾岩支撑，应采取必要的加固处理措施。