it is important that you regularly check your landscape if you live in an area that is vulnerable to sinkholes. If you are unsure whether or not you live in a sinkhole risk area, you can check with your local geological survey agency to find out more information. Signs to watch out for in terms of sinkhole development include small holes in the ground, if a structure is found to have cracks in its foundation, or any of these other common warning signs of a sinkhole. If you have discovered a sinkhole that is threatening a house or another structure, be sure to get out immediately to avoid a potentially dangerous situation. Then, contact your local emergency personnel and a building inspector. If you discover a sinkhole in the middle of a road, be sure to contact local law enforcement.
Most can be mitigated
Most sinkholes can be mitigated before they grow too large if they are identified and fixed early on. Most of the time, a sinkhole can be repaired before a dangerous collapse situation happens.
However, in those instances where a sinkhole can develop very quickly, it is important to be vigilant and aware of the warning signs, such as cracking noises in a roof or in a building’s foundation slab.
What about insurance and permits?
In most cases, sinkholes that occur on a person’s private property are considered to be their own responsibility. Insurance companies are much more likely to cover an evaluation and a repair if the sinkhole was naturally caused, such as by a subsidence event, than if it is caused by people, such as a collapsed or broken sewer pipe and drainpipe, broken septic tanks, buried trash, or improperly compacted soil following construction activities¹.
Typically, permits are not required to fill a sinkhole on private property (check with your local authorities to be certain). If the sinkhole contains groundwater (and thus, is connected to a local aquifer), however, a sinkhole fill permit will likely be required by a local Environmental Protection Authority or Water Management District to ensure that proper actions are taken to prevent groundwater contamination².
Small sinkhole repair
Smaller sinkholes, such as those that are 1 to 3 feet in diameter and depth can be easily filled in yourself¹.
- It is important to monitor the sinkhole to make sure that it does not grow any larger over time. If not, then it can be filled in.
- Dry-mix concrete or a concrete plug can be added to the bottom of the hole to provide a solid base.
- Add clayey sand. This will help to keep water from leaking out of the hole to prevent it from growing larger over time. A local contractor should know where to obtain the clayey sand. If clayey sand is unavailable, pure clean sand works as well. Rocks can also be used to help fill in the hole at this stage.
- Add sand and topsoil on top of the previous layers in order to help things blend in with the surrounding landscape. It is possible that you will need to add additional fill at a later time, but eventually the hole should become stabilized.
Engineering techniques used to fill sinkholes include injection of grout, engineered reinforced plugs, pins, and porous concrete².
But what about the very large… huge… and mammoth-sized sinkholes?
Large sinkholes typically require engineering professionals to properly repair them and to follow the necessary environmental requirements concerning local aquifers.
In some cases, cement and rocks are used to fill the very large sinkholes. However, it is possible that by simply using concrete alone to fill these big holes, the water may actually concentrate in other nearby areas, potentially leading to additional sinkhole formation.
The most preferred way to fix these very large sinkholes is similar to the method that is outlined above to fix smaller sinkholes, called the graded-filter technique, where there are layers of boulders, smaller rocks, and then gravel that are placed into the hole. The advantage of this technique is that it fills the hole while allowing for water drainage.
However, if the sinkholes are caused by older and decaying infrastructure, such as a leaky sewage system in your city, more sinkholes are likely to develop until such problems are fixed. This is especially the case if you live in a geographic area that is already vulnerable to sinkholes.
Fortunately, the dramatic cover-collapse type of large sinkholes that instantly swallow up buildings and cars are fairly rare³.
Some caution is advised!
Because many sinkholes are connected to aquifers, it is important that you do not fill them with any materials that could potentially be harmful to the groundwater supply, such as trash or chemicals. The best materials to use to fix a sinkhole are natural earth materials such as clean limestone rock, sand, and clayey sand².