[H-DS07] Landslides and related phenomena

[HDS07-13] Centrifuge investigation of the failure mechanism of landslide dam with different soil types subjected to raising upstream lake’s water level

*Raden Harya Dananjaya¹, Gonghui Wang¹ (1.Kyoto University)

Keywords:centrifuge test, failure mechanism of landslide dams, erosion process, breach discharge

Landslide dam (LD) is the natural damming of a river by displaced landslide materials. Because LDs are usually formed in mountainous areas, they can threaten human lives, the environment, and infrastructure if they failed due to the elevated water level of the barrier lake. To prevent and mitigate the possible disaster resulting from the dam break, a better understanding on the failure mechanisms of LDs is of great importance. Nevertheless, due to the fact that many LDs were formed in the remote mountainous areas and most of them failed immediately after their formation, their failure mechanisms are still poorly understood. Therefore, in this study, a series of centrifuge tests were conducted by using different types of soils to examine the effects of them on the failure mechanisms of LDs. In the tests, five soil types, i.e., tephra, Masado (weathered granite), silica No. 7, silica no. 8, and a mixture of masado and halloysite, with different densities and initial water contents. These models were subjected to an acceleration of 50g and an increase in the water level of upstream lakes. The results show that different failure processes, breach characteristics, and erosion phenomena occurred on the LDs of different types of soil materials. The failure process changes from progressive failure due to head-cut erosion on silica 7 and 8 (D50 = 0.005 and 0.16, respectively) to retrogressive failure on the rest of the soil types (D50 > 0.16). The breach characteristics also change due to the initial water contents in the same soil types. In air-dried water content models, the higher the initial density of the dam body, the higher the peak breach discharge. However, in the LDs consisting of soil material with 5% initial water content, the lower the density, the higher the peak breach discharge. Tephra soil models have relatively lower peak breach discharge than masado soil models. Furthermore, the halloysite has the effect of increasing erosion resistance. In some cases, the LD body vanished due to the occurrence of retrogressive landsliding phenomena that were immediately followed by quick overtopping erosion.