Insights into the stabilization mechanisms of coarse-grained landslide dams

Landslide dams are natural barriers formed by dynamic processes such as landslides and rock avalanches, which block river channels. Due to their loose structure and heterogeneous material distribution, they are highly susceptible to failure, posing significant hazards downstream. However, in the eastern margin of the Tibetan Plateau, there exists a widespread type of coarse-grained landslide dam formed by rock avalanches. Composed of massive boulders, these dams can maintain long-term stability, yet they have received little research attention. This study conducted flume tests on three representative types of coarse-grained landslide dams-the coarse particle group (T 1 , d₅₀ = 24.0 mm), the medium particle group (T 2 , d₅₀ = 8.9 mm), the relatively fine particle group (T 3 , d₅₀ = 1.3 mm) and performed a field investigation on a typical coarse-grained landslide dam (Mugecuo, Kangding City, Sichuan Province). The experiment results indicate that the coarse particles within the coarse-grained structure play a crucial role in the dam’s stability. During the initial formation stage, the large internal voids allow river water to pass relatively easily through the dam from upstream without causing overtopping. In the seepage stage, the massive boulders on the downstream slope are difficult to be entrained by the river flow at a given velocity, ensuring the overall stability of the dam. Under long – term fluvial scouring, the formation of a coarsened layer and a step-pool system by the large boulders resists intense fluvial erosion, thereby enabling the coarse-grained landslide dam to maintain long-term stability.