Effects of Grain Size Distribution on Landslide Dam Breaching—Insights From Recent Cases in China

Abstract

Landslide dams are common geological features in mountainous areas, which may have serious consequences due to sudden breaching of the dam. An effective emergency response requires rapid and accurate forecasts regarding the landslide dam breach process. However, most existing models use physical, mechanical, and erosion properties of the mean or characteristic grain sizes to represent the landslide deposits. The grain size distribution and variations in soil erodibility with the depth in the landslide dam are not considered, resulting in an incorrect estimation of the breach flow hydrograph. In this paper, a simplified landslide dam classification is presented based on the formation mechanism and grain size distribution of landslide dams. Additionally, the influences of grain size distribution on the residual dam height and breach process of landslide dams are analyzed. This paper proposes a numerical method to rapidly obtain the breach hydrographs and breach morphology evolution of landslide dams. The new method can quickly classify landslide dams according to geological survey data and predict the landslide dam breach process. Three types of representative landslide dams in China are simulated to validate the proposed method. The breach flow discharge is significantly affected by spillway excavation. This contribution can provide rapid prediction of the landslide dam breach process and can be used for the emergency response planning before dam breaching.

The Flims rock avalanche: structure and consequences

“…Once the lake was filled, which according to the estimate of von Poschinger (2005) took only one or two years, the dam was overtopped and incision of the natural dam started. Dam breach is complex and depends on the grain-size distribution within the dam and the erodibility of the dam material (Mei et al, 2021). According to Li et al (2021) dam breaching of natural dams occurs in three stages: (1) Incision with fine particles being moved leading to a notch in the dam crest, (2) Development stage with erosion on the down-stream side of the dam and mobilization of unsorted particles which are deposited in an alluvial fan, and, (3) Failure of the dam with rapid "two-helix flow" erosion deepening and enlarging the breach and resulting in collapse of the slopes.…”

“…The ensuing erosion processes by overtopping could have involved three phases (Li et al 2021): uniform bed erosion leading to a spillway and increasing outflow, backward erosion on the dam with increased outflow and enlargement of the spillway, and, finally, erosion of the outflow channel and rapid increase of discharge. The incipient stage with static overflow in natural dams is strongly influenced by the nature of the lithological composition of the dam (Mei et al, 2021). Fine-grained material is removed first and quickly.…”

Influences of Spillway Section Morphologies on Landslide Dam Breaching

“…The landslide dams' body is formed by the accumulation of landslide debris; its structure and constituents are strongly associated with the movement and material composition of slide mass. The rock slides, rock falls, and debris flows are the most prominent forms of slides that lead to the formation of landslide dams (Fan et al, 2020;Mei et al, 2021). 1) Rock slides are a phenomenon that results in rocks sliding and blocking the river when the driving force on a potential failure surface surpasses the resistance force.…”

Centrifugal model tests and numerical modeling on overtopping-induced breach processes of landslide dams

“…Landslide dams are widespread throughout the world. Extreme weather and geological disasters have occurred frequently in recent years, leading to increased landslide dams (Mei et al, 2021;Zheng et al, 2021). Unlike artificial dams, landslide dams are formed by a mixture of unconsolidated soil and rock in a naturally unstable state (Zhong et al, 2018).…”