Experimental study on morphological characteristics of landslide dams in different shaped valleys

Landslide dams pose enormous risks to infrastructures and communities in mountainous areas near rivers, with potential dam breaches causing catastrophic secondary hazards. The morphology of a landslide dam, essential to its stability, is highly influenced by its formation conditions, including the landslide type, material composition, and valley shape. However, the correlation between the dam morphology and these factors is poorly understood. A series of laboratory tests were conducted to investigate the damming process and deposition morphology across three different granular materials, two sliding widths, and three valley shapes. Detailed topography surveys of the dam deposits were conducted using a 3D laser scanner. The experimental results show that the width of the sliding path and valley shape have a significant effect on the morphology of a landslide dam. The dam deposits under a narrow sliding path are more concentrated and higher with steeper upstream and downstream slopes. The cross-valley profiles are dependent on the sliding width and valley shape for the well-graded gravel with sand (Soil I, GW) and poorly-graded sand with gravel (Soil II, SP) but are of the linear shape for the poorly-graded sand (Soil III, SP). The crest surface frontal angle of soil III is larger than that of the soils containing gravel (i.e., Soils I and II). The dam length increases as the valley shape changes from rectangular to trapezoidal and then to triangular, and shows opposite trends under the two sliding widths as the gradation becomes finer. The dam height decreases under the narrow sliding path as the soil changes from Soil I to Soil II to Soil III. In addition, larger particles (i.e., gravels) tend to accumulate on the surface and opposite side whereas finer particles (i.e., sand) tend to accumulate on the bottom and source side.