Experimental study on breaching mechanisms of landslide dams composed of different materials under surge waves

Abstract

After the formation of a landslide barrier lake, additional landslides in the lake area can generate huge waves, which may overtop the landslide dam and eventually lead to breaching failure of the dam. Since landslide dams are natural dams without compaction, the dam materials are heterogeneous, loose and highly erodible, so that the breaching process under wave actions is rather complex. Although a number of model tests have been conducted by different workers, several critical issues have not been addressed satisfactorily, including influences of landslide dam materials on breaching characteristics, stability criteria for landslide dams under surge waves, and differences in the breaching mechanisms by surge wave impact and natural overtopping flow. In this study, 9 flume tests were conducted to study the breaching mechanisms of landslide dams composed of fine, medium and coarse materials under surge waves of three wave heights. Compared with the natural overtopping condition, the breaching process under surge wave impact is much faster (the consumed time is only 2%-20%) and the peak discharge of breaching flood is 1.1-5.1 times larger. The surge waves accelerate the landslide dam breaching with more intense surface erosion and larger dynamic pore pressure. The total erosion volume and breaching duration decrease with the increase of mean particle size. With the increase of wave height, both the average erosion rate and peak discharge of the breaching flood increase. An empirical equation of wave climbing height for landslide dams was established based on the flume test results, which considers slope angle, surface roughness of dam and wave characteristics. The net overtopping height, ΔH, which is the difference between the sum of wave climbing height and still water level and the effective dam height, can be adopted as a useful index to preliminarily judge whether the landslide dam is stable or not under the impact of surge waves. When ΔH < 0, the dam is stable; otherwise the dam is unstable.