Abstract
On 6 July 2020, 3 h 40 min after rainfall stopped, a delayed debris-flow disaster occurred due to colluvium deposits in a hollow region (CDH) in the Chenghuangmiao Gully, Sichuan Province, China, resulting in 4 deaths and 27 injuries. This study explores the initiation process of the delayed debris flow and the cause for the delay. Field investigations, catchment geometry interpretation, laboratory tests, theoretical calculations, and fluid–solid coupling numerical simulation were performed to obtain landslide parameters and understand the mechanisms of the event. Results show that (1) the event was a giant low-frequency viscous debris flow. (2) It was initiated by the delayed landslide process under the influence of back-end confluence. (3) The debris-flow discharge in the main gully increased over 19.5 min. (4) The seepage process inside the CDH continued for 3 h 20 min after the rainfall stopped before the pore pressure and reduction in strength were sufficient to initiate the debris flow. This research provides new insights on delayed debris-flow disasters and can be a reference for improving disaster management systems, especially monitoring and early warning systems, thereby avoiding future casualties.
Highlights
Debris flows are triggered by high-intensity and short-duration, or low-intensity and long30 duration rainfall (Iverson 1997; Iverson et al 1997)
While the Chenghuangmiao Gully debris flow is recognised as a disaster, it is a geological process controlled by spatial distribution and temporal evolution features
Since 18:00 h on 5 July 2020, rainfall mainly converged into the colluvium deposits in a hollow region (CDH) in the form of surface and subsurface runoff, and the pore pressure of the CDH increased and its strength decreased
Summary
Debris flows are triggered by high-intensity and short-duration, or low-intensity and long duration rainfall (Iverson 1997; Iverson et al 1997). The debris-flow disaster initiated by the CDH landslide resulted from processes such as rainfall generation and confluence of streams, landslide, and debris flow (Chen et al 2007; Zhang et al 2019). As these three processes occur over various durations, they must be studied individually. From the onset of rainfall to the occurrence of debris flow, there were mature studies on back end confluence, seepage and deformation of the landslide, and debris flow respectively. We identified the process of debris flow initiation and the reasons for the delay in its onset
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