考虑河床坡度和泄流槽横断面影响的堰塞坝溃决过程试验研究

针对缺乏地形条件和工程处置措施对堰塞坝溃决过程影响研究的现状，采用4种河床坡度（0°、1°、2°、3°）和3种泄流槽横断面型式（三角形、梯形、复合型），开展了堰塞坝溃决的模型试验。通过分析堰塞坝的溃决流量、溃决历时、溃口发展和坝体纵截面演变过程，研究了不同河床坡度和泄流槽横断面对堰塞坝溃决过程的影响规律。试验结果表明：（1） 堰塞坝溃决过程可分为3个阶段。阶段I：溃口形成阶段，溃决流量较小；阶段II：溃口发展阶段，水流下蚀及侧蚀强烈，溃决流量到达峰值；阶段III：衰减-平衡阶段，粗化层形成，溃口停止发展。（2） 河床坡度增加意味着下游坝坡、坝顶及泄流槽的坡度增加，导致水流侵蚀能力增强，溃口下切迅猛，因此在0°~3°范围内河床坡度越大，峰值流量越大，峰现时间越早，溃决流量过程曲线越趋于“高瘦型”，且残留坝高越小。（3） 泄流槽横断面型式不同导致其槽深、槽宽和侧坡坡度不同，进而影响溃口发展和溃决流量。三角形槽的水土作用面积小，溃口下切及展宽速率最高，峰值流量最大，峰现时间最早；梯形槽的槽底高程最高，水土作用面积最大，溃口下切速率最低，峰现时间最晚；而复合槽介于前两者之间。试验成果将为堰塞坝应急抢险和工程措施的选取提供依据。

An experimental study of the breaching process of landslide dams with different bed slopes and drainage channel cross-sections

The breaching process of landslide dams influenced by bed slopes and drainage channels are still unclear. In this study, flume tests of landslide dams including four different bed slope angles (0°, 1°, 2° and 3°) and three different drainage channel cross sections (triangle, trapezoid and compound) are carried out. The effects of bed slopes and drainage channel cross sections on the outflow discharge, breaching duration, breach development and longitudinal evolution process of landslide dams are investigated. The results show that (1) the breaching process is divided into three stages. Stage I is the breach initiation stage with a slow breach erosion. Stage II is the breach development stage with a severe breach erosion. Stage III is the attenuating and re-equilibrium stage with the formation of an armored layer and the breach erosion gradually stops. (2) With the increasing bed slope angle, the dam crest and downstream slope angle increases, which enhances the shear stress acting on the soil and the deep-cutting erosion. Thus, when the bed slope is steeper, the peak discharge is larger, the arrival time of peak is shortened and the residual dam height is smaller. (3) Drainage channels with different cross sections have different depths, widths and lateral slopes, which influence the breach development and the outflow discharge. For the triangle drainage channel, its water-soil interface area is small, both the breach deepening and widening rates are the largest, while the peak discharge is the largest and the arrival time of peak is the earliest. For the trapezoidal drainage channel, its bottom elevation is the highest and water-soil interface area is the largest, while the breach deepening rate is the lowest and the arrival time of peak is the latest. The compound drainage channel is between the two former channels. The experimental results may provide important references for emergency treatment of landslide dams.