How Expansive Soils Affect Foundation Walls
Your foundation walls are at the mercy of the soils around your home. These soils exert vast amounts of pressure on your foundation walls, and circumstances can only get worse when those soils expand. The intensity of that pressure depends on what types of soils surround your home, the moisture content of those soils, and how deep your foundation goes.
Foundation walls are meant to support the weight of your home. That means vertical loads are their specialty. However, expansive soils create lateral, or sideways, forces that press against your foundation walls. When those forces generate enough pressure, your foundation walls will begin to buckle, cracking, bowing, and pushing into your home.
Given enough time, these lateral forces can cause your foundation walls to collapse entirely.
How Backfilled Soils and Virgin Foundation Soils Can Affect Foundation Walls
For new homes and new construction, contractors need to excavate to make space for the basement and foundation. That means disturbing hard-packed soil that was most likely undisturbed for an extended period. After the contractors finish the foundation walls and house framing, there will be space around the outside. The usual solution for filling this space is to use the dug-up soil to backfill the foundation walls.
However, because this soil loosens during the excavation process, it is significantly more porous and can absorb large quantities of water than before. Backfilled soil like this will swell when it rains, much more so than hard-packed earth. That creates hydrostatic pressure, and that pressure will affect your foundation walls.
Causes of Soil Expansion
There are three primary causes of soil expansion. Those are:
- Hydrostatic Pressure
- Frost Heaving
- Expansive, Wet Clay Soil
Moisture content in the soil is the root of each of these causes. Loose soil will expand as it absorbs water. Cold temperatures can cause moisture in the soil to freeze, causing expansion. Clay soil is much more water-expansive than other soils, exerting more pressure on foundation walls after heavy rains.