56 / 2025-08-15 15:22:38

Preliminary exploration of the formation mechanism of the accumulation layer landslide-debris flow-bridge collapse disaster chain induced by extreme rainfall

extreme rainfall；,disaster chain,formation mechanism

At around 7:40 am on June 24, 2025, a catastrophic collapse occurred in the approach section (K1264) of the G76 Xiamen-Chengdu Expressway Houzi River Extra Large Bridge in Sandu County, Guizhou Province. The day before the disaster, Sandu County was hit by a extremely heavy rainstorm of 212.2 mm. The landslide body is a tectonic erosion of the middle and low mountain accumulation layer, with a surface layer covered by about 14 meters thick gravel soil, and the underlying bedrock is shallow metamorphic sandstone. The volume of the landslide is about 5.6×10⁴m ³, and the main sliding direction is perpendicular to the bridge axis.

After the landslide starts, The 3#pier on the left first tilted due to lateral thrust. Under the coupling effect of left collapse load and residual landslide thrust, the right piers 2 # to 3 # became unstable, resulting in the collapse. Over 200m of bridge deck components mixed with landslide bodies to form debris sources, which were carried and discharged by the floods of the Houzi River. A debris flow accumulation with a length of about 150m and a thickness of 3-5 m was formed downstream in the valley, including concrete blocks, vehicles, and crushed stone soil.

It is suggested that in the future, bridge projects crossing valleys in mountainous areas should adopt measures such as optimizing the depth of pile foundation crossing cover layers and setting up slope groundwater dynamic monitoring networks to enhance the resilience of infrastructure.