Overview:
A new paper (Yi et al. 2023) ascribes this rainfall induced failure to the collapse of a fill slope on a road located above a miners' dormitory.
The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.
On 4 June 2023 the Yongsheng landslide in Jinkouhe District of Sichuan Province in China killed 19 people, located in a miners’ dormitory that was crushed by the failure. I blogged about this landslide (on the old blog site) immediately after the failure, and also tweeted about it:-
A brief initial review of this landslide has been published in the journal Landslides (Yi et al. 2023). The authors have undertaken a review of the “geological conditions, failure, kinematic characteristics, and the causes and mechanisms of slope failure”.
The Yongsheng landslide was about 140 m long and 23 m wide, with a volume of 4000 m3. It is located at [29.41, 103.03] – well done to Yi et al. (2023) for providing digital coordinates. The failure was triggered by rainfall, although the main period of precipitation occurred 24 hours before the landslide. The landslide travelled down a natural drainage line, which the authors term the “Shiban Gully”. It is notable that the rainfall over 72 hours preceding the landslide was in the range of 8 – 25 mm, and thus was not exceptional. In this context, there was clearly an additional factor at play.
In my original blog post I speculated on the likely cause of the landslide:
“Note that the crown is located on a hairpin bend on the road, with a small cut visible too. It is hard to believe that this landslide is not associated with the road; a working hypothesis might be that a fill slope was created on the downslope side of the hairpin bend, possibly with material from the road cut, to widen the road at this point, allowing vehicles to swing around the corner. This fill material might then have failed, loading the slope and progressively driving a larger failure. That fill is present is potentially supported by the fine-grained, grey material visible in the upper part of the landslide scar.”
This is the conclusion of Yi et al. (2023):-
“Historical satellite remote-sensing images of the area were scrutinized to comprehend the regional geomorphological variations surrounding the landslide… Remote sensing images from April 2013 demonstrated human activity within the Shiban Gully. A new road was constructed, and a triangular area distinctly different in color from the nearby vegetation emerged within the landslide source area…Analyzing these remote sensing images reveals the unstable area of previously discarded slag from road excavation construction within the landslide source area as the primary material contributor to the Yongsheng landslide.”
Yi et al. (2023) note that InSAR data also indicates that there was mining induced subsidence in the area, which may also have been a factor, but they also note that the fill slope was unsupported, which is more likely to have been a key factor, in my view.
Finally, it is notable that the landslide occurred in the early hours of the morning, when the miners were sleeping, which will have been a factor in the high loss of life.
There are maybe three key lessons to learn from the Yongsheng landslide, although none are new:
- Unsupported, loose fill slopes can be very dangerous;
- Poorly managed road construction greatly increases landslide risk;
- Locating high vulnerability facilities close to a gully, especially one that has been modified by human activity, should be unacceptable.
This was a preventable accident, which makes the tragedy all the more awful.
Well done to Yi et al. (2023) for publishing the research so quickly.
Reference
Yi, X., Feng, W., Shen, Y. et al. 2023. Catastrophic landslide in Leshan City, Sichuan Province, China: Fatality in a miners’ mormitory [sic] on June 4, 2023. Landslides. https://doi.org/10.1007/s10346-023-02180-x