September 18, 2011
Retaining Wall Failure, Gainesville, GA
Client: Residential Customer
This project involved replacing a poorly constructed residential retaining wall. The failed wall was 24 feet high, and was constructed in 4 foot increments of treated yellow pine timbers to get around permitting requirements (generally walls under 4 feet high don’t have to be permitted in most jurisdictions). The builder set the walls on a massive pile of uncompacted fill, and buried trash from the subdivision. The wall started to fail about 10 years after construction, which meant the contractor was nowhere to be found, and the Statute of Limitations had run out. The wall was showing a wide open tension crack at the top level, which can mean it is beginning to get global failure. We recommended a geotechnical firm come out and do an investigation. They couldn’t get a boring rig onto the site, so they did hand auger borings to about 12′ and found poor soil.
We designed three walls made of reinforced concrete to step up to the back yard. Excavation began, and the contractor encountered a deep trash pit about 15 feet below the ground. This raised the specter of serious global failure, so we recommended a different geotechnical engineer examine the site, Mr. Robert Turton of Oakhurst Geotechnical. Mr. Turton has many years of experience with soil engineering, and he performed a slop stability analysis to determine what soil improvements had to be done. He also monitored removal of poor soil and placement and compaction of fill. We had to change our wall design to reflect the new profile, and we were on site several times a week.
A year after the new walls were constructed, the 500 year storm hit the area, flooding many areas, and causing many structural collapses. Our walls remained stable, which we are certain is more than can be said of the original walls.