Jacksonville’s geology and weather patterns are mostly to blame for foundation issues in the city. Below, we’ll go over the specific factors that can damage your home’s foundation and why each is detrimental.
Rapidly Draining Soil
Soil is made up of three different particles: clay, sand, and silt. The ideal ground has equal parts of each to manage drainage and settling. Myakka, the soil in most of Jacksonville, is predominantly sand and contains a lower silt and clay concentration. The city’s coastal region has several other ancient marine soils, including Ortega, Kureb, Kershaw, Cornelia, and Blanton, all of which are also sandy and drain excessively quickly.
Rapidly draining earth is dangerous for foundations for two primary reasons, the first of which is the exposure to underground erosion. As rain falls and runoff rapidly soaks into the ground, it can quickly move the large sand particles that make up the soil. Even minimal deterioration of sand particles during drainage can create instability under and around your home, ultimately leading to an unsupported foundation.
Your concrete foundation relies on the soil for support to hold up your home above. If erosion leaves sections of your foundation without support, those sections tend to crack and sink more rapidly into the earth. The uneven sinking process – called differential settling – can very quickly lead to structural damage that compromises your home’s integrity.
Underground erosion is also dangerous because it can leave voids around your concrete. If runoff drains immediately around your home – a particular problem if gutters and downspouts aren’t used to redirect precipitation – it can erode the soil that usually contacts and supports your concrete. These voids can leave your foundation unsupported, but they can also fill with water and make water intrusion more likely.
Concentrated Rainfall and Flooding
Rapidly draining soil is most prone to erosion and the disparaging effects when runoff is draining into the earth, and Florida is well-known for its frequent showers and flooding.
The city experiences around 42 inches of rain per year, which is slightly above the national average. However, nearly ⅔ of the precipitation occurs between June and September, during which time the monthly rainfall is more than double what it is the rest of the year. This is partly because coastal Florida is prone to tropical storms and hurricanes during hurricane season.
The excessive and concentrated rainfall leads to a high risk of flooding, underground erosion, and voids around concrete foundations filling with water. As a result, Jacksonville homes are even more prone to differential settling, water intrusion, and moisture build-up.
The soil in Jacksonville is generally considered acidic. The ground nearest the coast is alkaline because of the effects of decaying and eroding seashells, but the soil becomes more acidic as you travel further west.
Acidic soil can deteriorate concrete foundations over time, potentially creating weaknesses that can cause foundation failure.
Lastly, Florida is underlain predominantly by limestone bedrock. Limestone is generally supportive, but it dissolves more readily than granite or shale bedrock when it’s exposed to water.
When runoff or groundwater interacts with the bedrock in Jacksonville, underground caverns and water channels develop as the limestone dissolves. These voids are the primary reason for sinkholes in Florida and the karst topography.
Weakness underground can create massive problems for foundations because the soil that supports your concrete relies on the bedrock below for rigidity. Underground caves and tunnels can eventually generate instability in the ground above, resulting in catastrophic differential settling under your home.