Abstract: The natural environment along south section of Sichuan － Tibet highway (in Tibet) is unique and fragile，which has led to many large scales of landslides and debris － flows blocking the main rivers，and caused severe catastrophe by outburst floods. Though field investigation of several typical dams along the section of Ranwu town to Peilong town in recent decades，main factors impacting the dam break had been identified through the methods of laboratory test and theoretical analysis. The results showed that the dam break is influenced by various factors such as the runoff and the channel characteristics of the main river，properties of materials，geometry and structural characteristics of the blocking dam and the angle between the dam and the main river，of which the downstream slope and the height of the dam are key influencing factors， affecting the break timing and the scale of floods.

Key words: South section of Sichuan-Tibet highway, landslide and debris － flow dam, break, influencing factors

摘要： 川藏公路南线(西藏境内)独特而又脆弱的自然环境导致多次大型滑坡泥石流堵塞主河事件，堰塞湖蓄水溃 决造成惨重的危害。在对然乌至培龙段近几十年曾经发生过的堵塞坝事件进行野外考察的基础上，运用室内试验 和理论分析相结合的方法对影响坝体溃决的主要因素进行研究，认为泥石流坝溃决是主河水流与沟道特征、坝体 几何形态以及坝体物质结构、坝体与主河夹角等多种因素共同作用的结果，其中关键因素为坝体高度和下游坡面 坡度，影响着溃坝时机和洪水规模。

关键词: 川藏公路南线, 滑坡泥石流坝, 溃决, 影响因素