25 January 2010
Ongoing massive retaining wall failure in San Antonio, Texas, USA
Posted by Dave Petley
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.
My Mother owns one of the houses directly below the slide. They were evacuated and no one is allowed anywhere near the area except with police escort– and only with good reason, such as medications or pet-pickup.If you look at your last picture:Continue the line of the bottom of your red box to the left and the second house you hit (not the corner house but the one to the left), is my Mother's. It looks like my dark van might be out front in the picture. (very possible since I visit often)Anyway, this whole mess is horrible and I can only imagine with the rain in the forecast for the end of the week…. it is going to get worse. Thanks for your report!
Lillie, if you read this would you mind dropping me a line at: [email protected], Dave
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.
Thank 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.RC
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?
The time stamp discrepancy is likely due to the fact that Dr. Dave is in the UK.-Peter
The picture with the red box around it is not a crack. This is a prime example of the water wasting that happens in our area to support new sod yards that have no shade in sight. During the summer time it reaches close to 100 degrees on a daily basis and people leave the water running on their grass constantly. This picture shows the water run-off from the house in the top portion of the picture with new sod. Continue to follow this story to learn more about the faulty retaining wall that was built not once, but twice. The wall fell the first time in November of 2006 before any houses were built on the hill side. I smell a lawsuit!
From 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.
Bing 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. My 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 http://www.RetainingWallExpert.com
This type of retaining wall is built all over this area. It IS a gravity wall, the gravity structure happens to be at the bottom of the wall and goes in a backwards batter below the earth instead of forward making the wall sloped on the facade. The backwards batter/gravity device is made up of rip rap rock and possibly some concrete slurry. That is the theory anyway. The guys who build these walls boast about the speed of which they build them, mostly with very cheap (but stable) limestone like what you see in the photos and VERY cheap labor. They generally pour a rough concrete beam at the bottom to start the stacking on the taller walls. I worked on a project in this area for a large resort where there is 93' of grade change from the front entry to front door. The developer wanted to bench 650 or so surface parking spaces on that slope. So, there will be walls similar to these holding about 8 bays of parking up this slope with only about 8' from curb to top of wall! We went through hours upon hours of meetings with structural engineer and guys who build these types of walls. Structural engineer was against stacked stone gravity walls of course. The gravity wall builders had their own structural to stamp drawings. We will see if it holds! The walls have been up for a year or so and there are MANY on the site. I think the tallest at about 30' holding up a POOL and spa. I think they are all built with a 12:1 batter.
Our webpage, “San Antonio ground collapse and sinkhole gets national attention” (http://www.homeownersoftexas.org/San-Antonio-Sinkhole.html) continues to grow, with over 23 videos now posted. We also add reader comments to the most significant news stories and continue to write on our own blog (http://homeownersoftexas.blogspot.com/2010/01/texas-builder-at-center-of-san-antonio.html).
Heard from Channel 12 that a laundromat is providing free laundry and dry cleaning service to any family in the area affected by the retaining wall break.Details: http://www.MinuteWash.comHope it helps…
Good job on the blog.I saw this about a week and a half ago. Any updates as to what is happening here? Are they going to rebuild the retaining walls? If so do you know what products they are looking to use here? I would love to have some more information on this. I am so sorry to all those who have homes in the area! Best wishes to all of you!thanks
Many waterfront properties all over the world having retaining walls or seawalls are aging to the point of needing repair or worse, replacement. Failure to provide proper weep hole relief has resulted in water being trapped behind the wall causing erosion, pressure, and wall failure.Natural erosion can be controlled (possibly even prevented altogether) with the use of a proper weep hole drain. Water pressure can be released without taking the valuable soil into the bay or canal further preventing erosion or sink holes. The Jet Filter flush mount system can be easily installed and maintained from the waterside of a new or existing seawall and retaining wall. The purpose of weep holes is to relieve hydrostatic pressure from behind the wall. Properly maintained, the seawall should last a lifetime without major repairs. The patent pending Jet Filter relieves hydrostatic pressure on almost any wall design.“The fix permits drainage without erosion (about 6 months now). I used to be able to see multiple areas where there was flow over the top of the wall (from rainfall accumulations behind the seawall). I have seen none since completing the Jet Filter installation”. (Sonny, Homeowner Gantt Lake, Alabama).As a former marine contractor, creator and inventor David Gentry has been providing weep hole drains throughout the world to marine contractors, engineers and homeowners. The materials used in the manufacturing of the Jet Filter are UV protected, durable and consistent with the life of the seawall/bulkhead. For additional information on the Jet Filter System contact David Gentry at 239-825-4508 or visit http://www.jetfiltersystem.com.
Information you shared is really helpful, thanks for sharing information.
Many waterfront properties all over the world having retaining walls or seawalls are aging to the point of needing repair or worse, replacement. Failure to provide proper weep hole relief has resulted in water being trapped behind the wall causing erosion, pressure, and wall failure.Natural erosion can be controlled (possibly even prevented altogether) with the use of a proper weep hole drain. Water pressure can be released without taking the valuable soil into the bay or canal further preventing erosion or sink holes. The Jet Filter flush mount system can be easily installed and maintained from the waterside of a new or existing seawall and retaining wall. The purpose of weep holes is to relieve hydrostatic pressure from behind the wall. Properly maintained, the seawall should last a lifetime without major repairs. The patent pending Jet Filter relieves hydrostatic pressure on almost any wall design.“The fix permits drainage without erosion (about 6 months now). I used to be able to see multiple areas where there was flow over the top of the wall (from rainfall accumulations behind the seawall). I have seen none since completing the Jet Filter installation”. (Sonny, Homeowner Gantt Lake, Alabama).