SAN ANTONIO — A retaining wall at the Rivermist community in San Antonio, Texas, failed on Sunday, Jan. 24, prompting an evacuation of 91 homes. The homes are part of a development by Centex Homes, a Texas-based developer and builder. According to an update provided by Centex, investigations are still underway. Centex will also be hiring engineering firms and soils professionals to help determine the cause of the soil movement.

The same update by Centex indicated that the wall was rebuilt in early 2007, “following indications that the wall was not performing to expectations. The decision was made to completely rebuild the wall and substantially reinforce its foundation.”

Initial reports on the collapse indicate that it is still too early to tell the cause of the shifting soil and the subsequent wall collapse. According to local geologists and the Edwards Aquifer Authority, the houses sit on a combination of Buda limestone over a layer of Del Rio clay. The limestone near the top of the hill is stable, but the clay layer at the bottom expands and contracts during wet and dry periods. According to Jeff Neathery, a San Antonio-based geologist, the failure “appears to be strictly an engineering issue of building on the side of a hill.”

The city of San Antonio initially responded to the failure by suspending the certificates of occupancy for the 25 homes closest to the open trenches and rubble. Additional measures by the city have included placing an inspector at the neighborhood to monitor construction and hiring an independent structural engineer to evaluate the homes.