۱- Introduction

۲- Wave flume experiment

۳- Test results

۴- Pore water pressure

۵- Discussion

۶- Conclusion

References

Abstract

In recent years, large magnitude earthquakes have caused the formation of a large number of landslide dams. The rising water level in the landslide lakes may induce a large number of landslides in the lake areas. When landslides rush into a lake area, large-scale surges may be produced and would then strongly impact on the dam stability and cause a breaching process. To understand the erosion failure modes of dam bodies caused by surges and the variation in the pore water pressure in the dam body, large-scale wave flume tests were carried out in this study. Six groups of comparative tests were carried out to study the two main influencing factors, namely, the upstream water level and the wave height. It was found that (1) when subjected to surge waves, the landslide dam stability is determined by the difference (ΔH) between the effective water level (the sum of the water level and the overlapping wave height) and the effective dam height (the dam height after lowering due to local sliding); (2) when ΔH < ۰, overtopping does not occur, and the landslide dam remains stable. A stable upstream erosion surface eventually forms, the surface slope angle decreases and the erosion volume increases as the wave height increases; when ΔH > ۰, the dam is overtopped and breached by the next waves; (3) During dam breach by overtopping with surge waves, the erosion in the breach initiation phase is much faster than by overtopping without surge waves, but the difference in the breaching development phase is not very significant; and (4) the pore water pressure close to the upstream slope is much more sensitive to the action of the surge waves than deeper inside the dam body.

Introduction

A landslide dam is formed by blockage of rivers with the soil and rock materials from landslides, avalanches, debris flows etc., which are triggered by earthquakes, rainfalls, snowmelts etc. (Peng and Zhang, 2012). In recent years, high magnitude earthquakes have caused the formation of a large numbers of landslide dams. The naturally-formed lake is called landslide lake or barrier lake. After the formation of a barrier lake, a rapid rise in the water level may cause a large number of landslides. When a landslide slides into the lake, it may produce huge surge waves (Hager et al., 2004; Koo and Kim, 2008). The surge may greatly erode the landslide dam, causing a much more rapid dam break and more serious flooding than that under normal conditions, which could be a great threat to human life and property downstream (Blown and Church, 1985; Evans and Clague, 1994; Soares-Frazão and Zech, 2007). A landslide of 300 million m3 slid into the Vaiont Reservoir in Italy in 1963, causing a tragic surge with wave heights as high as 300 m. The surge wave spread 1.4 km in 7 min and killed 3000 people in five towns (Tang and Lee, 1992). In 1983, a glacial avalanche rushed into the Homathko River in British Columbia, Canada. The surge caused by the avalanche overtopped a moraine dam and released a volume of water as large as 6 million m3 . Actually, the largest existing landslide dam, lake Sarez formed in Tajikistan in 1911 with a height of 800 m and a lake volume of 17 billion m3 , is threatened by an enormous potential landslide in the lake area only several kilometers upstream of the dam.