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.