Local homeowners occasionally observe the development of sinkholes in their yards and express concerns about them possibly becoming large enough to engulf their homes. However, sinkholes in North Georgia are different from those in Florida due to the underlying geology of the land.
In parts of Florida, many areas have limestone as the bedrock. The ground water is somewhat acidic and it slowly dissolves the limestone forming underground cavities. When the cavity enlarges to the point to where it can no longer support the ground above, it will collapse forming a sinkhole. Often buildings, roads, and other man-made structures are damaged or destroyed by them.
The good news is sinkholes in the Metro Atlanta area rarely become that severe.
Here, the predominant causes are construction debris and plant material that settle and decay forming an underground void. Hidden by layers of soil, it usually goes unnoticed until it eventually caves in forming a sinkhole.
If one appears on your property, avoid walking on it. Standing on the stable edge, use a shovel to dig through the surface. Search for evidence of any leftover building materials or decayed trees to confirm if this is the problem. If you discover any of these materials, you have a construction sinkhole. Use a long wooden or metal rod to probe the sinkhole. Hitting the solid earth a few feet down is a sign of a small sinkhole that can usually be repaired by the homeowner.
If when probing the sinkhole, you discover a pipe with standing or flowing water in the cavity, chances are you have a broken water or sewer line. Often rainwater washes the soil into the pipe. Over time, as more soil is lost, the above ground collapses. If this is the case, contact your local water and sewer provider before taking further action.
To repair sinkholes, first remove any large pieces of debris that has not decayed. Then add fill dirt in one foot layers. After each layer of soil is applied, pack it firmly.
Continue this process until the hole is filled. Make sure the soil is thoroughly compacted or it could settle again and cause another sinkhole. Then plant grass and other suitable plant material on top.
However, if the cavity under the sinkhole is so large you are unable to reach the sides or bottom with the rod, or if you have lots of water and muddy soil, the problem is far more severe and can be potentially hazardous. In this case, you should not attempt to fill it in due to risk of injury and possibly causing greater damage. Contact a geotechnical or soil consulting firm for assistance. They have the expertise and the resources to fix the sinkhole.
Timothy Daly is an Agricultural and Natural Resource Extension Agent with Gwinnett County. He can be contacted at 678-377-4010 or firstname.lastname@example.org.