2 July 2018
Guang’an: a dramatic retaining wall failure video
Posted by Dave Petley
Guang’an: a dramatic retaining wall failure video
Youtube has a cool video showing the impact of a retaining wall failure in the city of Guang’an in Sichuan Province, China. The event reportedly occurred early in the morning yesterday (6:50 am on 1st July 2018):
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The event reportedly involved the failure of a 50 m section of retaining wall during heavy rainfall. Interestingly, Liveleak has a second video that shows a part of the failure of the wall from the foot of the slope. This still is taken from that video:-
Retaining wall failure at Guang’an in Sichuan, China. Still from a video on Liveleak.
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I am not quite sure what to make of the images from the videos of the state of the materials behind the unfailed sections of the wall after the failure:-
The aftermath of the retaining wall failure in Guang’an, Sichuan Province, China on 1st July 2018. Still from a video on Liveleak.
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The resultant landslide was a classic slump, with the roadway moving downwards and outwards as the support at the toe of the slope failed. The Chengdu Economic Daily has an article about the landslide (in Mandarin). This article indicates that cracks had started to appear in the fill behind the wall on 22nd June, and that the authorities had been aware of the problem. These cracks enlarged rapidly on the day of the failure, such that local people were able to provide warnings that a failure night occur. The landslide occurred in several phases, starting at 6:50 am, and there was a significant failure at about 11 am too. In total about 50 households have now been evacuated. The slope was reportedly about 30 m in tall. Interestingly there is quite a large section of this wall that remains standing, as the still below shows:
The aftermath of the retaining wall failure at Guang’an in Sichuan, China. Still from a video on Youtube.
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Managing the remaing sections of that wall will be challenge in the forthcoming rainy season.
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
Rain is a concern because the soil’s shear strength is reduced as its’ water content increases?
[In essence yes. The remaining sections of the wall may have been weakened by the failure of these sections. D.]
It looks as if much of the adjacent fill behind the remaining section of wall also slid out, creating a large void?
Loose fill, poor or no subdrainage, no internal fill reinforcement (no Tensar or equivalent – wall looks more like a decorative facing rather than a structural element to my eye). The wall that slid out may not have had much of a footing if it was largely decorative.
>>Interestingly there is quite a large section of this wall that remains standing,<<
For now….
With the apartment blocks uphill from the site, I would bet that stormwater disposal practices from these areas played a part in the failure.
I remember a distant cousin proudly showing us pictures of his smart, new apartment block in Mexico City. It had a lovely swimming pool in the gated grounds, an impressive retaining wall cut into the steep slope behind. I asked if the pool had a flexible liner such that an earthquake’s cracks would not empty it. He laughed. Then I asked how the retaining wall was anchored and drained. He laughed, but I must have set him to think. Six months later, we got a ‘change of address’ card…
Totally agree… very bad fill behind the wall, probably the same at the toe, no drainage seen in the pictures, such a high wall should be thick and anchored enough if not reinforced with geogrid… it’s more an engineering failure than a soil failure to me.