The lifetime and dam breach modes of landslide dams are related to the material characteristics of the rock debris or the sediment which collapsed to block rivers, for example, the permeability coefficient of the dam and dam strength, and the strength of natural dam and their permeability are closely related to particle distribution of the dam material composition. According to literature, the particle sizes of dam material composition vary greatly, and the upper part of natural dams often contains a shell made of coarse particles and gravels, the bottom is composed of very fine particles. Thus, the mechanical properties of various parts of natural dams are not uniform, they are related to particle sizes, composition and mode of stacking and arrangement.
This research used the v-shaped slope apparatus to simulate the valley terrain. Tests of slope collapse accumulations were carried out through changing the various influencing factors such as particle sizes, slope, and distances. The accumulations were treated with solidification. Blocks of materials were removed to take photos to build a profile for imaging analysis. Finally, a test of mechanics was performed on the accumulations.
The following conclusions have been obtained through the research results: (1) The angle of repose did not show a significant difference due to different testing methods, the angle of repose became more gradually fixed after the particles exceeded a certain count. The shape of valley bottom does not affect the naturally stabilized angle of repose to maintain the final landslide mass. (2) In a valley landslide process, after the particles fell to the valley bottom, they often hit the other side and bounced back to cover the landslide lass or mixed with the particles that came down later. Because the natural landslide mass formed went through the dynamic compaction effect, its slope stability is higher than its static angle of repose. The primary factors in order of significance that affect the slopes of landslide mass were long drop distance, steep slope, and coarse particles. (3) The porosity of landslide mass reduced slightly as the sliding distance increased, the higher the fine particle count the lower the porosity. In addition, it was found out through imaging analysis and sieve analysis that the coarse particles of landslide mass were mostly located in the upper layer, and the fine particles in the lower layer. The distribution of coarse and fine particles became more uniform as the sliding distance increased. (4) The porosities differed between the upper and lower layers in the landslide mass. When applied in the analysis of permeability of natural dams, it differed from the traditional single permeability coefficient, the correction made to the calculation of seepage volume due to the upper and lower permeability coefficients caused a somewhat different result from the traditional single seepage volume. This can be used as a reference to estimate the dam breach time in the future.