中文摘要：

溃坝洪水突发性强、危害巨大,计算既有工程溃坝洪水时的溃口范围至今都是假定,不能反映复杂坝体结构在不同荷载作用下溃决的实际。为了较合理定量判定溃口范围,在研究拱坝结构体系和溃口特点的基础上提出了单元组概念,采用可靠度来表征单元和单元组是否安全可靠,给出了单元组和整个结构体系可靠度计算方法;提出和采用贯穿坝体的单元组失效概率,来评估溃口发生部位、范围,并根据结构承载能力可靠度（失效概率）评价指标定量确定溃口几何尺寸;找到了采用可靠度（或失效概率）评价指标定量确定溃口范围的一种新方法。并对招徕河碾压混凝土双曲拱坝实例进行了计算分析,验证了计算理论与计算方法的科学性,可供计算溃坝洪水时确定混凝土坝溃口范围参考。

英文摘要：

In order to quantitative predicate the failure scope of dams , this paper put out an element group conception which is consisted of a group of elements throughout the dam body. The dam body safety status is simulated by a 3D finite element model. A new structural reliability method for calculating the dam breach scope has been found , by which the failure scope of dam can be predicated quantitative. The Zhaolaihe RCC arch dam is taken as an example to show the applicability of the new method.