Stumped by a Sinkhole
What's causing the sinkholes in this owners yard? Sinkholes appear when the subsoils are removed or are liquefied into caverns or other underground openings.
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Q: I have a problem with holes in my yard, and I hope you can help me. At first I thought the holes were caused by an animal, but I keep filling them with dirt and they keep sinking. The holes are right up against the house, and now I'm worried that the foundation could be damaged if the sinkholes keep growing. Do you have any idea what could be causing the holes?
A: Sinkholes appear when the subsoils are removed or are liquefied or the subsoils "hourglass" into caverns or other underground openings.
In areas where underground mining is prevalent, sinkholes often appear in a process called mine subsidence. Older mines deep in the earth collapse, leaving voids in the soils above the mine. Over time the surface soils settle to fill the voids in the earth. The area affected by mine subsidence can be several hundreds of yards wide and damage to homes or other buildings in the subsidence zone can be devastating.
If mine subsidence were present, your neighbor's property would also be experiencing some soil displacement.
Hourglassing can also occur if the home's building lot contained vegetation that was covered during construction.
When I was a contractor, one of the homes I had to repair was built over an old drainage ditch that had been filled in with tree stumps and other debris instead of compacted soils, which are required for stabilization. Over the years, as the stumps decayed, the ground settled, causing serious damage to the home's foundation. Sinkholes appeared in other areas of the yard.
Liquefying of the soils can be caused by earthquakes, which you would be aware of, underground springs or improper control of surface water.
Gutters that overflow, downspouts that drain too close to the foundation, retaining walls that are not drained properly, loss of vegetation on a hillside, disturbing of the soils (digging) and not adding erosion control can lead to liquefying of the soils. This can also be classified as removal of the soils in some instances.
Water will seek its own path, which can lead to erosion on the surface of the yard plus erosion in the subsoils just under the surface of the yard. Subsoil erosion can leave sinkholes. Usually, when I see sinkholes next to a foundation, I suspect a broken sewer pipe. When water rushes through the broken sewer, the soils around the break are pulled into the sewer pipe and flushed away. Over time a sinkhole appears.
The break is usually next to or near the foundation because the home has settled at a different rate than the sewer pipe. Before digging up the yard to check for sewer breaks, make sure there are no water leaks. Have the water company read your meter and then make sure everything in the home that uses water is turned off.
After about 15 minutes, have the water company read the meter again. If no water has been used, there is no leak. If large amounts of water have passed through the meter, then the sinkhole could be from a water supply leak.
In any case you need the help of a licensed, qualified plumber.
(Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home-improvement questions at PO Box 268, Evansville, IN 47702 or send him e-mail at firstname.lastname@example.org.)
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