How Are Sinkholes Formed?
Common Signs of Sinkhole Activity...
Cracking Walls, Foundations, Pool Patios, or Driveways...
Cracks that manifest themselves on the exterior walls of a structure are definitive of some degree of settlement. Stair stepping cracks are commonly seen just off the corners of a structure and at opposite corners of windows, (i.e. upper left corner and the lower right corner). You may also see stair stepping cracks in the middle of a long wall. Other locations around your property are vulnerable to cracking due to sinkhole activity including: foundations, pool patios, and driveways.
Sticking Windows or Doors
If you are having trouble closing doors and windows on your property you could be experiencing sinkhole activity. As your foundation begins to sink from the underlying sinkhole activity, your door and window frames will buckle and become uneven.
Leaning Trees or Fenceposts...
In determining if your property is at risk of sinkhole damage, it is important to not ignore the signs that are evident around your property. Any geological change in your property or neighboring property could result in sinkhole damage to your home. These signs can be seen in the form of leaning trees, fenceposts, or other structures that are not necessarily considered a structure of occupation.
Causes Of Foundation Settlement
Normal Florida Settlement
Most structures settle to some extent during the first two years they are on a pad. Hairline cracks are common, this is generally understood to be normal Florida settlement. When cracks continue to widen and grow beyond hairline, it may mean that shallow soils were not properly compacted during the construction phase of the structure. This is not normal and should be investigated by a geological engineer familiar with the soil conditions in your general area.
Geological Settlement
When hairline cracks become evident after the first two years it is no longer considered normal Florida settlement. This type of settlement is generally caused by a geological problem in the deeper strata of soils. There are several reasons for geological settlement.
Shrink, Swell Clay
When clay has a considerable amount of plasticity and is located in the first 15 to 18 feet below the structure, drought times will cause the clay to shrink, rainy seasons will cause the clay to swell. During the drought period settlement can happen to such an extent that it compromises the integrity of the foundation of the structure. When this happens the capacity of the soil no longer supports the weight of the structure and cracking will appear due to broken foundations.
Subsurface Sinkhole Activity
Sub-surface sinkhole activity is another cause of structural settlement resulting in cracked walls and broken foundations. Acidic water moves through soil strata to limerock and eventually dissolves and erodes the rocky soil below creating voids deep within the earth. As time passes the soils above the voids drop which loosens the soils above it. The loosening of the soils will produce a chimney effect opening towards the surface when clay is present. This results in the loss of ability of the upper layers of earth to support the structure above it. When clay is not present the result is the same, but instead of a chimney there may only be an enlarging depression manifesting in the ground that may open dangerously wide and deep.
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