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Sink holes can be tricky to repair

Posted: Sunday, May 04, 2008

Help! I have sink holes in my yard.

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Suddenly, these holes appeared in my yard. The soil just disappeared. I don't see any evidence of animals digging. It's as if the Earth just opened up and a hole appeared.

A few weekends ago, the No. 1 thing on my to-do list was to fill in all the holes in my yard. These are not sink holes, but were created by rotting stumps.

Ten to 11 years ago, I cleared the area to build my house. Most of the trees removed were large pine trees. Most of the stumps were removed, but some just had the top part of the stump removed.

About three years ago, a number of holes starting appearing in my yard.

In fact, last summer as I was mowing the grass I stepped on a spot and the ground gave way. It was another stump hole. After I fixed the holes in my yard, another hole appeared, so I have another one to fill in.

How do you know that they are stump holes and not sink holes like they have in Florida?

In Florida, the bedrock is a different rock than what we have in Columbia County. Limestone is the main type of rock that makes up the bedrock in the areas where sinkholes are most common. In Columbia County, most of the bedrock is granite. Granite doesn't give way like limestone.

Rotting stumps are not the only causes of holes appearing in your yard. Construction debris buried in yards could be another cause of sinkholes. This can be a problem around older homes. With changes in laws and the inspection process, this practice is a thing of the past.

To make sure a rotting stump or construction debris is the cause of the hole, you need to do a little inspection. Take a flashlight and look in the hole. If it is stump or construction debris, you should see pieces of rotted wood, bark or other building materials.

If you don't find any of these, check for wet soil -- you could have a water leak. If it is a main pipe or sewer line, you can have large holes. If you can't reach the bottom or reach from side to side of the hole, call your water department.

If you have holes appearing in your yard, you need to fix them because they are a safety hazard. A few years ago, I stepped in one of the holes in my yard and twisted an ankle. Most people think that to fix the hole all you have to do is replace the soil. This might work on small holes, but large holes must be repaired properly.

The best way to repair the hole is to make it larger at the surface. This accomplishes two things. First, it will show you if the hole is larger than what you can see. I was fixing one of the holes in my yard that was about 8 inches in diameter. As I was preparing the hole it kept getting larger. As I dug, the hole increased to about 20 inches in diameter. Grass and soil about 4 inches deep was on top, but there was a void under the sod.

Once you have found the true size of the hole, you need to remove all of the rotted wood or other organic matter that you see. If not, these items will continue to rot and will leave a void.

Then fill the hole with soil. Put 10 to 12 inches of it in the hole and pack it. Once it is packed, add more soil and pack. Keep doing this until the hole is full. I then like to add water to help settle the soil more. Then wait a day or two to see if any settling has taken place in the hole. If so, add more soil.

Then, you can plant grass over these areas if they are in the lawn. In other areas, wait a year or two before you plant shrubs or trees to give the soil extra time to settle. If you plant shrubs or trees in the hole before it has finished settling, the plant could settle, which would cause problems with its growth. The roots would go into a state of decline because of the change in the amount of oxygen and water reaching them. Also, as the plant settles it could cause the tree to grow at an unsafe angle.

So the next time you have an unexplained hole in your yard, try to remember if there was a tree there, or look for rotted wood.

Columbia County Extension Agent Charles Phillips can be reached at (706) 868-3413 or by e-mail at charlesp@uga.edu. The Extension Web address is www.ugaextension.com/columbia.



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