What To Know About Sinkholes
Sinkholes are a naturally occurring geological feature throughout Florida. Generally speaking, soil in Florida is formed atop of limestone, which is a very porous type of carbonate rock. As rainwater, which is somewhat acidic, filters down through the ground to the limestone layer, which is alkaline, the acidic rainwater causes the alkaline limestone to slowly dissolve over time. As the limestone dissolves, it breaks down into smaller and smaller particles - sometimes the dissolved limestone particles become so small that they are no longer classified as rock - they become classified as clay.
As the limestone dissolves underneath the soils, gravity slowly pulls the soils above the limestone into the voids created by the dissolving limestone. This downward movement of the upper soils is referred to as "raveling." Raveling soils is a common feature of sinkhole activity.
Think Of An Hour Glass
An easy way to picture how sinkholes form is to think of sand in an hour glass. The hole at the bottom of the hour glass is very tiny - but as gravity pulls the sand downward, through the hole, there is a ripple effect on the surface of the sand in the hour glass. In a sense, this is how a sinkhole works - most sinkholes that form in limestone are fairly small, sometimes only a few feet in diameter. But like the hole at the bottom of an hourglass, as soils are pulled down into the sinkhole, there can be a ripple effect on the surface.
Homes Not Built To Move
The impact of sinkhole activity is most felt on homes and structures built on the surface of soils - typically homes and smaller commercial buildings with a "slab on grade" foundation. Most homes are built by pouring a 12 inch to 18 inch concrete foundation on the earth. The walls are then attached to the concrete slab, and then the roof to the walls. Everything rests on this concrete slab foundation. The weight of the concrete slab, and thus the weight of the entire structure, is supported by the soil immediately underneath of the concrete slab. Normally, this type of construction is very stable and is a very cost effective means to build homes.
Here’s the problem - these homes built on slab on grade foundations are not meant to move! If the soil underneath the concrete slab slowly erodes, the soils can no longer support the weight of the foundation and the home. When this happens, it can cause the home to sink, sometimes very slightly, over time. Remember - slab on grade homes are not really designed to withstand movement of the foundation! When part of the foundation starts to sink, it can cause stress on the foundation and the home in ways that the home was not built to withstand. The result is something called "differential settlement."
Differential Settlement
Differential settlement is a structural engineering term. It means, essentially, that different parts of a structure, such as a home, are settling at different rates. When this happens to a home built on a slab on grade foundation, the results can be devastating. The stresses from differential settlement will manifest themselves through a number of different mechanisms, and usually at the weakest points in a structure.
Signs
An extensive list of symptoms and signs is listed on this website. But general points of weakness where stresses from differential settlement will show up are:
- Cracks in the inside and outside of the home, along the floor, walls and ceiling
- Cracks around doors and windows
- Doors and windows that don’t work normally
- Cracked, loose or hollow floor tiles
- Leaking during heavy rain
- Strange noises at night
- Not level floors
- Kitchen and bathroom cabinets not being level
- Plumbing issues, or higher than normal electric or water bills
- Pools losing water
Where Do Sinkholes Form?
Sinkholes can form almost anywhere in Florida, from the areas around Miami and West Palm Beach, to Jacksonville, Tallahassee, Orlando, Tampa, Ft. Myers, Panama City, and all points in between. Some people might say sinkholes only form in the area just north of Tampa - but this is incorrect! Sinkholes can and do form throughout the state! Just because you don’t live in an area known for having a high number of sinkholes nearby doesn’t mean you cannot have one. If your home is experiencing damage that is consistent with damage caused by sinkhole activity, you may be experiencing damage caused by sinkhole activity!