The Wall
Professor Turner asks his Tuesday morning geology class “has there been geology in the news?” lucky for me I had just seen a story about how a local neighborhood had a retaining wall which collapsed over the weekend. I raise my hand and tell my professor about the news, only to be asked “well why do you think it happened?” only one single word popped into my mind at that moment. Erosion.
Later on I asked Professor Turner how can erosion cause so much damage. He states that “Clays are softer rocks, that can swell when they get wet, shrink when they dry out, and rocks can slip on top of them. This makes them a difficult rock on which to construct a firm foundation. In addition, it appears that the builders used fill materials to build up and level off the area. These fills should be compacted prior to construction to meet certain engineering requirements.” This led me to believe that maybe the developers of the neighborhood (Centrex Homes) had not obtained the permit to build the retaining wall.
Well in fact Centrex Homes did not obtain the permit, Centex Homes was required to get a permit for the 1,000-foot-long stone wall that would be used to hold up the hill where several homes were built, but because Centrex Homes did not apply for the permit, therefore they did not comply with the building regulation codes. So the area that they had been build up behind the retaining was never stable and this lead to the evacuation of about 25 homes after a landslide began on Sunday, but in today’s paper only 3 houses were determined to be unstable.
According to Costas Georghiou P.E. of Pierce Goodwin Alexander & Linville the failure could have been caused by “the foundation not being compacted properly, poor drainage behind the wall due to the lack of weep holes in the wall that would allow the water to filter through, and possible heavy loads on top of the wall during home construction”. He explained that without these weep holes water accumulates behind walls and increases horizontal pressure on the retaining wall. In addition, the excess water lubricates the soil particles which reduces their strength and contributes to the sliding of the whole slope. Even if they did get their permit the contractor should have known how to construct the wall properly, so that the last few days of heavy rain would have made the wall weak due to soil saturation.”
Every evacuated resident has been provided with accommodations, but as far as compensation for their homes and belongings; officials have not reported if there will be any yet.