Slope Failure

  • More retaining wall problems discovered in a San Antonio subdivision

    After a towering retaining wall collapsed and threatened scores of homes last year in the San Antonio neighborhood of Rivermist, an obvious question arose: How safe were the untold number of other residential retaining walls in the city?

    Under city code, walls in San Antonio over four feet tall were supposed to go through a permitting process. But until Rivermist, that permitting process rarely happened in new subdivisions — despite the widespread use of large walls to sculpt hillsides in the rapidly growing Texas Hill Country.

    In other words, no one at the city could vouch for the safety of other retaining walls, many of which are 20 feet high or taller.

    After the collapse at Rivermist, the city announced that all tall residential walls built in the last three years had to be verified as safe by an engineer and permitted. So far, most walls have passed muster.

    But one subdivision with 14 retaining walls is still having problems.

    It’s called the Heights of Crownridge, located on the far North Side by the Crownridge Canyon Natural Area. Jen found out about it after a concerned resident emailed her photos of a long vertical crack in a huge wall in the middle of the subdivision.

    Jennifer and I had written a bunch of stories about the problems with retaining walls in San Antonio. After Jen got the tip, we drove to Crownridge over the weekend with baby Sophie sleeping in the car. The subdivision was unfinished — streets were completed but only a handful of homes had been built. There were no lawns. Just sun-baked dirt and rock.

    And there are a lot of tall retaining walls. The one the tipster alerted Jen to is huge:

    Retaining wall at the Heights of Crownridge in San Antonio

    And sure enough, there was a long, very noticeable crack on the northern section. This is part of the crack:

    Cracked retaining wall at the Heights of Crownridge in San Antonio

    Jen sent an open records request to the city for more information about what was going on at the Heights of Crownridge. A couple weeks ago we sat down in an office of the city’s Planning and Development Services Department to read a stack of letters and engineering plans related to all the retaining walls in the unfinished subdivision.

    No engineering plans had yet been received for the big wall we checked out. (I later interviewed Scott Rozier, the owner of Rosch Co., which built the wall with the crack. He stood by his work.)

    But there were problems with other walls. Going through the documents, Jen and I had a case of deja vu. It turned out some of the same people involved with the wall at Rivermist also designed and built a wall that later cracked at the Heights of Crownridge.

    Engineer Russell Leavens designed the Rivermist wall, and it was built by Gravity Walls Ltd. They also designed and built a different wall at Crownridge that suffered from a large crack and was deemed unsafe. This wall was on the southeast corner of the subdivision, which we hadn’t known about. Engineer Tim Theis determined that the wall had not been built according to plans.

    At Rivermist, city officials had also claimed that Gravity Walls Ltd. did not build the wall according to engineering plans.

    Theis mentioned problems with the particular type of retaining wall used in both subdivisions. Gravity walls rely on their sheer mass to remain stable. But once they’re built, it’s difficult for inspectors to make sure the walls were constructed right. That problem was noted at Rivermist and also at Crownridge.

    As we reviewed the documents, a city engineer who was handling the case came by the office. It turned out construction had been on hold at some lots for months as the concerns about the retaining walls were being sorted out.

    The pile of documents included maps showing the location of each retaining wall and who built it. Coupled with the info we learned from other documents and interviews, the maps helped me build this interactive feature that showed readers what was going on in the subdivision:

    View Retaining wall problems at the Heights of Crownridge in a larger map

    We could have cranked this story out faster if Jen hadn’t made the open records request. But the documents gave us details that we might not have otherwise known, such as the connection to Gravity Walls Ltd. Plus, we can post the paper trail online for readers to check out for themselves.

    It simply pays to dig up pertinent records … even if it slows you down.

  • 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.

  • Retaining wall not built to engineering specifications

    Retaining wall at the Hills of Rivermist

    Jen and I wrote a follow-up story today about the sinking neighborhood in San Antonio called the Hills of Rivermist:

    The retaining wall that collapsed last week and jeopardized a neighborhood built by Centex Homes was built with less mortar than what engineering plans called for, according to city officials who inspected the wall Friday.

    “Staff determined that the retaining wall was not built in accordance with the design provided by (the) design engineer,” Assistant City Manager T.C. Broadnax wrote in an e-mail to his boss, Sheryl Sculley, Mayor Julián Castro and the City Council.

    “For example, the building plans for the wall show limestone mortared throughout the wall. Based on field observations of the failed portion of the wall, mortar was not installed according to the building plans.”

    There are many different types of retaining walls. The one at Rivermist is called a gravity wall, which relies on a heavy mass of mortar and stones to remain stable. So if a contractor skimps on the mortar in the core of the wall, the wall becomes lighter and it can become unstable.

    Here’s the city e-mail describing the lack of mortar inside the wall. The city also set up a new Web page that provides updates about Rivermist. Residents can also report concerns about retaining walls near their homes.