14 March 2012
A really impressive landslide in Japan
Posted by Dave Petley
The Daily Yomiuri has a report on a slow ongoing landslide in Kokugawa district of Itakura Ward, Joetsu, in Niigata Prefecture that has so far destroyed 11 buildings. The landslide is reported to be 750 metres long and 150 metres wide:
The sandbag wall described in the article appears to be an attempt to protect the houses in the bottom left side of the photo.
I’m having a hard time imagining how a sandbag wall would do much to stop the movement of a landslide. Would it be effective? Or is it only possibly effective because the main mass of the slide appears to be moving another direction anyway?
[yes Anne, you are quite right. I suspect that this is to try to keep the margins of this earth flow away from the houses, plus to stop water draining from it from flooding them. Of the slide struck the wall head on then it is very unlikely that it would have any effect. It is fair to say that sand bag walls are not a conventional landslide management and mitigation tool!
The sand bag walls can be very effective especially if the landslide if very fluid as they can be used to slow down or redirect the flow. Often the sandbag or similar barriers are deployed using locally available materials as a temporary measure to reduce the risk to the public whilst properly engineered solutions are developed and constructed.
We regularly use PCB’s (concrete Jersey barriers) or water filled Triton barriers as temporary landslide protection for roadways. We have video of boulders up to 4 tonnes coming down slopes into these barriers and being arrested. We recently had about 500 tonnes of mud and boulders come down from about 30m above a major highway and the barriers effectively captured the material with about a 25mm lateral displacement. The solution is not pretty, but works fair enough as a temporary measure.