Experimental study on the seepage failure mechanism of climbing-type landslide dams with spatially nonuniform depositional structures

Background Climbing-type landslide dams are unique natural geostructures characterized by loose depositional structures and distinct particle-size sorting along the sliding direction, making them highly susceptible to internal seepage failure during upstream impoundment. To clarify these risks, this paper replicated the spatially nonuniform depositional structure of landslide mass using a specialized release chute within a large-scale physical flume, and comprehensively analyzed the seepage deformation characteristics of climbing-type landslide dams by evaluating the spatial particle distribution and seepage field variations across distinct parts of the dam. Results The findings reveal that the internal depositional structure of climbing-type landslide dams is highly complex, exhibiting pronounced particle-size sorting; the average median particle sizes D 50 at the front, middle, and back parts are 12.79 mm, 4.11 mm, and 2.86 mm respectively. Crucially, the entire failure evolution follows a distinct three-stage cascading chain: progressing from initial seepage initiation in the downstream left coarse zone and its upward L-shaped expansion during the storage period, through intensive downstream slope collapse and piping enlargement during the steady seepage period, to ultimate piping beneath the crest that triggers an initial breach and overtopping failure. Additionally, critical particle initiation conditions for internal erosion were established, indicating that the maximum erodible particle diameter D max is proportional to the square of the seepage velocity and inversely proportional to the internal friction angle. Conclusions The critical seepage failure mechanism of climbing-type landslide dams manifests as a cascading disaster chain, wherein slope instability induced by seepage retrogressively triggers concentrated piping, structural collapse, and subsequent overtopping breach erosion, indicating that early-stage micro-leakage and anomalous pore water pressure fluctuations should be recognized as key early warning indicators for proactive hazard mitigation.