Most people remember the occasional news story about a sinkhole opening up and swallowing cars or large buildings. While we were recently looking over a house, a friend of mine literally stumbled on a sink hole in the backyard. On the surface, this hole was about 3 feet wide, but we couldn’t tell how deep it was. Our concern is that the hole was only a few feet from the back of the house. We wondered if this was the reason we saw cracks in the brick foundation under the back deck.
What causes sinkholes? Large sinkholes that open in roads or under houses are caused by the erosion of softer minerals underground, such as limestone or dolomite. Water runoff eats away slowly at the stone over time and creates a pocket of air. The ground above begins to sink as dirt and debris begin to fall into the hole. Eventually the ground loses strength and caves into the underground pocket, compromising the structures that are built on it.
Sinkholes may also be caused by buried trees, stumps, trash, or building materials during construction. In a similar way, these items decompose over time and are washed away by rainstorms. A pocket is formed underground and dirt above begins to fall in and create a hole or cave-in.
When the climate changes from drought to heavy rainfall, this can cause sinkholes to form more quickly. This is especially a concern in Atlanta. A good example is the two-year drought Georgia experienced in 2008 and part of 2009. About the time Georgia and Alabama began fighting over the water supply, the climate shifted to an El Nino state and it rained daily for almost 2 months. Interstate highways as well as neighborhood streets were all under water. Such a dramatic shift in climate can cause more erosion which in turn may cause sinkholes to form more easily.
How are sinkholes remedied? Remediation depends on the size and location of the hole. First the hole must be completely excavated to expose the entire cavity. The hole is filled with dirt and solidly compacted every 12 to 18 inches to prevent further erosion. When the hole is completely filled and compacted, the ground covering can be replaced. As you may guess, a large sinkhole may be a long, expensive remediation process.
Warning signs – So how can we tell if a sink hole is forming on a property? Some of the signs are subtle and could be attributed to the house settling. However, multiple signs may need a watchful eye in case a sinkhole is forming.