Sinkholes in Florida: Causes, Prevention and Damage Repair

It is a homeowner’s worst nightmare: having their beloved home – and biggest investment -- partially or completely swallowed by a sinkhole. 

Sinkholes have always been a part of Florida life, mainly because of geological conditions that allow groundwater to dissolve subterranean limestone, creating underground voids and caverns that occasionally cause cave-ins and collapses known as sinkholes. But the combination of growing population, new construction and alterations to Florida's water supply has resulted in increased property damage due to sinkholes. When loss of life accompanies property damage, this local phenomenon becomes national news.

In the wake of the sinkhole tragedy that claimed the life of a Florida resident, more area homeowners have begun to worry about the ground their homes sit on. Insurance agents and sinkhole repair companies have been swamped with phone calls.

The detailed information presented here has been provided by L.R.E Ground Services, a Brooksville-based foundation repair company that has been repairing sinkhole damages in FL since 1989.

Subterranean erosion can cause three different types of sinkholes

 Sinkholes are a depression in land surface created by the displacement of soil and/or water circulating and causing the limestone underneath to dissolve. Sinkhole activity is a worldwide phenomenon, with a higher prevalence in areas where the rock below the land surface is limestone, salt beds, carbonated or other types of rock that can be dissolved by water. As the water washes away the sediments, underground caves begin to form.

What makes sinkholes particularly terrifying is the fact that the surface land can remain intact, with no signs of sinkhole acidity until the support underground is gone and the ground suddenly collapse into a huge pit, without warning.

There are three types of sinkholes: solution sinkholes, subsidence sinkholes, and cover-collapse sinkholes.

Solution sinkholes occur when rainwater erodes the limestone under a thin layer of soil, causing shallow sinkholes to gradually form on the surface.

Subsidence sinkholes occur when the soil layer over the limestone bedrock is mainly comprised of sand. The water erodes the limestone, creating voids. The sand then filters down into these voids and sinkholes gradually appear on the surface. 

Cover-collapse sinkholes -- the scariest type of sinkhole -- occur where the soil layer is deeper over the sinkhole and more cohesive than sand. This soil, which is more consolidated because of clay and root content, can bridge voids that form in the underlying limestone, effectively hiding a subterranean cavern. But at a certain point the weight of the soil (or the soil plus a man-made feature like a house or paved road) is too great. So a sudden collapse occurs, swallowing everything that lays on the surface, including homes. 

Sinkholes can also be caused by human activity, such as the occasional collapse of an abandoned mine, or in urban areas by water main breaks, collapsed sewage pipes, and excessive extraction of groundwater.  They are also a concern in new urban developments, when construction alters the natural water drainage patterns and the water seeks new diversion pathways.

Are there any signs of sinkhole activity under my home?

Gradually forming sinkholes under your home can cause foundation settlement, and in some cases, signs of sinkhole acivity can be noticed. Typical signs include:

• Cracks on foundation walls.
• Cracks in drywall, especially at top corners of window & door openings.
• Cracked or out-of-level floors, slabs, sidewalks or driveways.
• Obvious low or sunken areas on your property.
• Mildew or wet areas around the foundation.
• Leaks in the ceiling and roof.
• Nails popping.
• Windows or doors that stick or stop working because of settlement or skewed openings.

What should I do if I suspect sinkhole activity under my home? 

If you suspect sinkhole activity in your property the first step is to call your insurance company right away. They will most likely assign an adjustor to handle the case, and hire a structural engineer to inspect the house. The engineer will then issue a report that will include a remediation plan, if needed.

That report is then used to obtain quotes from foundation repair contractors. It’s smart to get at least three quotes from experienced and reputable local companies that have experience in repairing sinkhole damage. They should come and thoroughly inspect the site, issuing a proposal based on the structural engineer’s recommendations.

You will then be able to have the contractor of your choice perform the repairs. This contractor will be in charging of filing all the required paperwork and pulling all the required permits. After completion, they should deliver an engineering completion report, along with warranties and guaranties.

What are the options to repair sinkhole damage? 

Compaction grouting is the only proven method of repairing a sinkhole and stabilizing the soil. The process involves drilling holes in the ground to access the underground cavities. Casings are then inserted, and a grouting compound is injected into the voids, to fill voids and stabilize the soil.

 In some cases, foundation underpinning might be recommended to stabilize a sinking foundation. In this process, steel piles are driven into the ground with powerful pneumatic equipment, up to the point where they reach solid, stable soil or bedrock that can reliably hold the weight of the building.  These piles are then used to raise the foundation back to its original position. As the weight of the entire building is transferred to the supporting piles the foundation is stabilized.

For peace of mind, always select companies that offer a long-term, transferrable warranty for any foundation-related work.

It is extremely important for a homeowner in Florida to always have current sinkhole insurance, even after a sinkhole is effectively repaired. Mother Nature is unpredictable and you never know what is going to happen a few years down the road.