In the United States there is an interesting developing story about a large-scale retaining wall failure that is causing the collapse of a housing estate in San Antonio, Texas. The housing development, called the Rivermist subdivision, is the one shown in the Google Earth image below. It is still under construction. The marker shows the approximate location of the slide, as far as I can tell:
According to the media reports the slide started moving on about Friday is now sliding at about 4 inches (10 cm) per hour. There is a pretty clear video of the slide here (but note that this is definitely not a sinkhole as the report suggests).
The slide is far from trivial. These images, from this site, appear to have been taken a day or so ago:
More recent reports and images suggest that the slide has moved a great deal since these pictures were taken. More than 80 houses have been evacuated.
The area of the failure is, as far as I can tell, shown on this Google Earth image. This is two years old and was taken before the houses in this area were built. I have highlighted a rather peculiar feature that runs across the road on this image:
Interesting! The worst-affected houses in this area already look beyond recovery. I wonder how many more will be affected. Personally, I would not allow people to stand or to wander around anywhere near the toe of that wall, but maybe I am overly-cautious. This is clearly a tragedy for the families involved.Updated here
Dave - nice job on this. You have a good eye to be able to spot that "issue" with the road from 2008. I hope the homeowners read your blog.
ReplyDeleteThank you for your information. I live in the cul-de-sac directly below this old crack in the street, and one block from the landslide. We are being allowed back in our house today but I am not going until I see what happens over the next day or so and can get further explanation from the fire dept tonight. This is a nightmare for all involved! I am just thankful that no injuries have been reported.
ReplyDeleteRC
How can these posts be time stamped 8:30 and 9:30 PM on Jan. 25th? I'm looking at the clock right now, and it is clearly 4:34 PM, Monday, Jan. 25th - what's the deal?
ReplyDeleteFrom what I can gather on the net, this is a huge slump failure of a clay slope. Is this in-situ soils or placed? It isn't a retaining wall failure because there is no retaining wall at the toe of the slope. I see no reinforcement, only a very small amount of stone covering the slope. A stone wall is a gravity design and would be massive. Concrete could be smaller, but there isn't any. Fabric walls would have huge amounts of fabric behind them to create the gravity wall. This doesn't. So there was no retaining wall, only a facade. I have designed hundreds and hundreds of walls in Appalachia, and have never had one even slightly fail. This is just poor engineering, from what I can see in the pictures.
ReplyDeleteBing has some nice aerial photos prior to home construction. To me, it's evident soil was built up on the downward slope and then capped with a facade. The sewer mains were likely placed prior to filling with dirt. At the depth of failure, that soil would likely have been limestone if it wasn't man made. The lack of a piled/heavy concrete retaining wall on the lower ~6ft probably allowed the failure. The fill dirt simply slid down the eroded limestone slope, since it had no significant retaining structure. This is all presummed. I'm sure anyone with money at stake will find 'the real problem'. I've lived in San Antonio for 18 years, and from my memory, this configuration pretty common, but there's typically some anchored and reinforced concrete at the base. If you look nearby, between wind walker and rainbow view in Helotes, there is a much better retaining wall where earth was removed up to the limestone instead of added over the slope.
ReplyDeleteMy best wishes to all involved, particularly the home owners. I pray your needs are served first.
Excellent blog - much appreciated. Being a Geotechnical Engineer, I appreciate the time and effort you put into your website. I also specialize in landslides and retaining walls, and this obviously is a big problem for lots of people (homeowners, developers, wall builders, design engineer-if there was one). Safety is paramount now; however, GATHERING INFORMATION NOW is important to accurately determine cause of failure. Don't go in there and obliterate everything, thus destroying data and information along the way which will be needed later to determine the cause of failure. I'm a registered PE in 16 states (not TX yet, but that can be done quickly). See my website at www.RetainingWallExpert.com
ReplyDelete