• Was cracked retaining wall built correctly?

    Engineering plans for retaining wall at the Hills of Rivermist

    New documents offer more information about the retaining wall that collapsed at the Hills of Rivermist, a neighborhood in San Antonio built by Centex Homes. Comparing the wall’s engineering plans to a memo describing how the wall was actually built shows the retaining wall might have lacked crucial features:

  • The original engineering plans for the wall, drawn up by Russell Leavens of Enterprise Engineers Inc., show the wall was designed as a gravity wall, which relies on its own weight to remain stable. The contractor that built the wall is the aptly named Gravity Walls Ltd., owned by Chun Lambert. We wrote this story about a city inspection that concluded the wall wasn’t built with enough mortar. Less mortar means less weight, which could destabilize a gravity wall. Lambert hasn’t returned our calls.
  • After our story was published, city officials continued inspecting the wall. Development Services Director Roderick Sanchez wrote this memo last week laying out the reasons why he believes the wall can’t be patched up. Sanchez offers more details about how the wall wasn’t built to Leavens’ specifications. For example, the wall is missing a layer of limestone and fabric that was supposed to be set behind the structure to capture water and properly drain it through weep holes at the bottom of the wall.

    “There are multiple reasons why the wall may have failed,” Sanchez concluded. It could have been a combination of design failure, construction failure, or soil failure beneath the wall, he wrote.

  • The memo was posted on a city Web page set up to provide daily updates about Rivermist. The city posts new information at the end of every business day.

  • Maps, plats, and photos of the sinking neighborhood in San Antonio

    I’m helping out with the coverage of the “slope failure” at the Hills of Rivermist, the neighborhood in San Antonio where shifting soil and a buckled retaining wall jeopardized homes. Here are some useful resources to learn more about what happened:

  • Express-News photographer Jerry Lara shot recent aerial photos of the neighborhood showing the scale of the damage.
  • Bing features a cool 3D map of the site, and in Google Earth you can view a series of aerial photos to see how the hillside was flattened and sculpted over time.

    Google’s tutorial explains how to check historical imagery of an area. The wall collapsed where Treewell Glen curves into Valley Well:

    View Larger Map

    Typing in an address of one of the affected homes, such as 12003 Treewell Glen, will zoom Google Earth to the spot. Then click on the clock symbol in the toolbar, and you’ll be able to view aerials dating back to 1995.

  • This is a plat of the site filed at the Bexar County courthouse. It identifies the engineering firm that designed the neighborhood as Pape-Dawson Engineers, a well-known firm in San Antonio. Gene Dawson told me the engineering work for the retaining wall was done by another firm. The plat also shows there’s a sewer line under the area that collapsed:

    The Hills at Rivermist Plat

    Centex says it still doesn’t know what caused the slope failure.

    You can search for and view plats, deeds, and other documents filed at the Bexar County courthouse for free at a Web page set up by County Clerk Gerry Rickhoff. The site requires you to register.

  • City Manager Sheryl Sculley sent this e-mail chain to Mayor Julian Castro and the City Council explaining the city’s permitting process. Centex Homes says it was unaware a permit was required for a retaining wall.
  • Centex released a public statement about the slope failure. “Centex has been focusing on stabilizing the homes and is now entering the investigation phase. We have retained several well-respected engineering firms and soils professionals to aid in our efforts to accurately determine the cause of the soil movement. We will not speculate on the underlying cause of the soil movement at this time, but will provide additional details when they become available.”
  • On Twitter, the incident has its own hashtag: #slopefail, coined by police reporter Eva Ruth Moravec who was among the first reporters at the scene on Sunday. Props do have to be given to KSAT for their own hashtag — Eva said they came up with #sinkholegate.
  • You can check the credentials for engineers in Texas at the Web page of the Texas Board of Professional Engineers. You can verify an engineer is licensed by searching here, or if you’re a data monkey you can download zip files of the entire roster of all engineers here. Disciplinary actions taken against engineers are listed here. You can browse the disciplinary actions, but they’re not easily searchable. You can search for a specific name by typing “http://www.tbpe.state.tx.us” in Google and then the name.
  • Feel free to get in touch with me with any tips or story ideas about #slopefail — here’s my contact page.

    Updated 1-29-10: Two more useful Web pages that are new:

  • Centex set up a Web page about the collapse. The company is posting announcements, a FAQ page, and a form that allows residents to pose questions online.
  • The San Antonio Express-News set up a Web page with all our news stories, photos, videos, and graphics about the sliding hillside.