How expanding soil affects foundation walls
Backfill soil behaves differently than the unexcavated, “virgin soils” farther away from the foundation. Backfill soil typically absorbs more water and expands more, exerting pressure against the foundation.
The soils around your foundation can put a lot of pressure on your foundation walls! The amount of pressure will vary depending on three factors:
- The types of soil around the home
- How much moisture is in the soil
- How deep underground the foundation is built
Since foundation walls are designed to support loads from above rather than lateral (sideways) loads, expanding soil can cause foundation problems.
When the pressure from outside the basement walls is greater than the wall can handle, the wall will begin to crack, bow, and push inwards. Factors such as expansive clays, hydrostatic pressure, and freezing water can create too much stress on basement walls, causing them to push forward and even collapse entirely over time.
Backfilled soils & virgin foundation soils
As water builds up in the soils around your foundation, hydrostatic pressure increases against your basement walls, potentially leading to damage.
When the contractors who built your home dug the hole for your foundation and basement, they dug up mounds of the hard-packed earth that was there — some of which may have laid there untouched for hundreds of years or more. As foundation walls and house framing were completed, the empty space around the foundation needed to be filled. Contractors typically backfill foundation walls using some of the excavated soil that was removed to make room for the basement.
The excavation process breaks up and loosens the soil. Because of this, backfill soils will always be more permeable, or water-absorbent than the hard-packed earth beyond. When it rains, the water will collect in the backfilled soils, exerting hydrostatic pressure against foundation walls. This is known as the “clay bowl effect”.
What causes soils to expand?
Wet foundation soils have a number of possible ill effects on the soils. By adding water to soils, you can cause them to expand, add weight to the soil, and ultimately lead to enormous pressure on the foundation walls.
Wet soils can lead to foundation damage in these three ways:
Expansive, wet clay soil
While sandy soils remain stable as water passes through them, soils rich in clay undergo significant changes based on their moisture content. When clay type soils dry out, they shrink significantly — so much that the ground can become covered with cracks. But after a heavy rain, the cracks are gone and the soil is fully saturated with water.
Because clay soil absorbs so much water, it expands during wet weather. Expansive clay soils can put enormous pressure on your basement or foundation walls. When the pressure becomes more than the wall can handle, the wall will begin to push inwards.
Hydrostatic pressure is the pressure exerted by a fluid due to the force of gravity. To understand how hydrostatic pressure can damage foundation walls, imagine how much heavier soil becomes when it’s soaked with water. When the weight of water is added to the weight of the soil, you’ve got much greater pressure pushing against a foundation wall.
Hydrostatic pressure effectively amplifies soil pressure against a foundation wall. When pressure exceeds the foundation wall’s ability to withstand it, the wall will begin to bow, buckle, tilt inward at the top, or move inwards at the bottom.
In areas with cold winter climates, frost heaving can sometimes put enough pressure on foundation walls to make them fail. When water turns to ice, its volume increases by about 9%. If wet soil experiences a deep freeze, the wedging or heaving force that results can be extremely powerful.
Frost heaving can put literally thousands of pounds of force against your foundation walls, causing cracks, bowing, and heaving.
Do you need a foundation repaired?
When your foundation is showing signs of bowing, buckling walls or any other foundation issues, the foundation experts at Complete Basement Systems are here to help. Our experienced professionals can identify the issues affecting your home and recommend the right solutions for your needs. Contact us online to get a free estimate in Denver, Colorado Springs, Aurora, Littleton, Cheyenne, Fort Collins, Thornton, Arvada, Westminster, Pueblo, Boulder, Greeley and the nearby areas.