The Rivermist subdivision in San Antonio, Texas is on the move again - and it is a rotational retaining wall failure

The woes of the families displaced by the slope failure at the Rivermist Subdivision in San Antonio, Texas have been exacerbated by a new phase of movement. AP Texas News reports that heavy rain has triggered additional cracking of the wall, and the movement of some debris. However, the houses at the top of the slope are apparently not moving.

I have been wondering why they are so confident that the wall won't fail. In an earlier post I suggested that this is not a simple retaining wall failure, given the toe scarp - a couple of subsequent commenters agreed. These aerial images, from My SA news show that this is the case:

The key part of the image is actually at the bottom of the first image above, although once you have your eye in you can see these features in the other image too. This is an annotated version of that first image:


This landslide is clearly not a simple retaining wall failure. It is a rotational slip in the slope that has caused the retaining wall to fail. It is not surprising that they do not expect the wall to collapse during these rains as the wall is being rotated to lean backwards by the failure.

Of course, as per the comment below, ensuring that the retaining wall would not be affected by this type of rotational failure should always be a key part of the design process for such structures. I suspect that this will become a textbook example of the problems that can affect retaining walls.

The San Antonio retaining wall collapse - did the developer have a permit?

Reports suggest that ground movement has ceased in the Rivermist subdivision, which suffered a fairly spectacular retaining wall failure over the last few days. Attention is now focussing upon that retaining wall - and in particular on why it failed. This is a pretty key issue given the potential liabilities and its magnitude - the wall is 1000 feet (>300 m long).

Press reports note two interesting aspects of this accident:

1. The City of San Antonio has released a statement that says "The hillside collapse yesterday within the River Mist subdivision that damaged several homes was a result of an improperly constructed retaining wall, as well as improper compaction of fill on which homes were constructed by the developer, Pulte Homes. The developer did not obtain the required City construction permits for the retaining wall that collapsed."
2. Some reports suggest that this is the second time a retaining wall has failed at this site: "One neighbor who was among the first homebuyers in the subdivision set among rolling hills on the outskirts of San Antonio said he was initially told no homes would be built on the crumbling ridge because it was too steep. Romeo Peart, 32, said one retaining wall failed several years ago before the current one was built and homes were constructed above it" (Washington Post).

I should also add that I am not sure that this is a particularly simple retaining wall failure, based upon the image below (from here):

In particular, it appears that the slope / small retaining wall below where the man in the green jacket and hat is located has also failed. I wonder why?

Finally, I thought I'd embed this video, at least in part for the picture shown before the video starts, which is a somewhat surprising image in my opinion:



The video itself provides an interesting overview and a verification that a section of the wall had needed rebuilding on a previous occasion.

Ongoing massive retaining wall failure in San Antonio, Texas, USA

Updated here

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