Under Florida law, an insurance company must undertake a sinkhole investigation, at its expense, if the damage to the structure is consistent with sinkhole as a cause of loss. This damage is usually associated with "stair-step" or other cracking that suggests movement of the underlying soil. These cracks occur due to the loss of structural support being provided by the soil itself.
At the time of the investigation, the engineering firm shall accomplish two things: (1) determine whether the damage is associated, either directly or concurrently, with sinkhole damage; and (2) if the damage is not associated with sinkhole activity, the actual cause of the loss. Engineering firms, due to the focus being primarily to determine if the damage is sinkhole related, often overlook this second category.
The most common alternative causes of such damage include expansive clay or "clayey soils," the presence of excessive organic-laden soils and loose, unconsolidated sand. In addition to issues with soils, many times alternate causes of foundational damage may be associated with construction materials that may be reacting to moisture changes or load changes in the home.
Expansive Clay and Clay Type Soils
Clay itself is both a particular size and a soil material. Unlike most other soil materials (e.g. rock, sand or silt), clay reacts with water, through a series of complex geochemical processes. Like a kitchen sponge, clay takes on and gives off water. When dry, the clay will dehydrate, or "desiccate," and like a sponge, will lose its volume or occupy a smaller space. When the clay takes on water in this state, like a sponge, it will then expand and enlarge in size. This is bad in the context of soil materials because soils that do not maintain a particular volume tend to move - up or down. When placed beneath a home, the damage caused by the expansion and contraction of a clay soil can be dramatic. This is due to the fact that the mere movement of a clay-type soil by only small distances can cause concrete, stucco and other construction materials to suffer damage. There are a lot of variables in associating a loss with clay, many of which are misunderstood or oversimplified by inexperienced engineering firms.
Not surprising, but most soil material contains an expected percentage of plant material or other organic components. The amount of organic material in a soil should not exceed a certain threshold. If it does, it will potentially create soil material that is not suitable for construction. For example, it would be unwise to construct a home upon several feet of organic peat (yes, seen it), even if the upper 10 feet is covered with "healthy" soil material. This is because soil material with excessive organic material loses volume much like a pile of leaves losing volume once decay begins. Again, just with clay-type soils, this is a complicated process and the mere presence of organic material in the soil must be considered with several other material variables before a home may be damaged by this condition.
Loose, Unconsolidated Sand
This condition is the result of soil material which has lost its cohesion due to a wide variety of potential causes. Sand, under pressure, will take on a particular shape and act in a particular manner. When homes are built, they are said to "supercharge" the sandy soils by making them compress the soil together. Sometimes, due to changes in the water content near the building, the sand will "unconsolidate," and lose its ability to support a structure. This would best be described as a condition, and not a cause of the damage. This is due to the fact that the presence of loose unconsolidated sand, itself, does not tell what caused it to reach this state. For example, you could have loose sand, which became loose due to sinkhole activity. There should also be concerns that the description of sand as unconsolidated cannot be measured by any objective standards, and is subject to considerable differences of opinion.
To learn more about alternative causes of foundational damage from soil types, please contact Corless Barfield Trial Group at 813-498-1623.