4 February 2010

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

Posted by Dave Petley

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.