Straight Talk About Foundation Soils

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 (hydrostatic pressure)
  • how deep underground the foundation is built

Expansive Soil Can Cause Foundation Problems

Expansive spoil is distinguished by the presence of swelling clay minerals that can absorb a significant amount of water molecules. When expansive soils obtain moisture, they expand or swell up. Likewise, when expansive soils lose moisture, they begin to shrink.

Since foundation walls are designed to support loads from above rather than lateral (sideways) bearings, expanding soil can cause foundation problems.

Hence, when rain or improperly channeled water enters too quickly and oversaturates your backfill soil, that excess water will exert immense pressure against your foundation walls. This is known as hydrostatic pressure.

The Problem with Hydrostatic Pressure

Water is heavy! And it can build up underneath the floor, pushing upwards against your foundation. This is known as hydrostatic pressure and will enter the home through any weak point it can find.

When that pressure bearing down becomes greater than your below ground basement or crawl space walls can handle, the affected walls will begin to crack, bow, and push inwards.

As pressure continues to build over time, what starts as a hairline crack will worsen and can eventually result in extreme wall failure, typically in the form of buckling, shearing, or even complete collapse.

In addition to hydrostatic pressure caused from heavy or steady rains, factors such as expansive clay (which all homes in Georgia reside on) and water thawing too quickly after a winter freeze can also create too much stress on basement walls, causing them to crack, bow, and deteriorate.

soil level graphic against home

Backfill soil behaves differently than unexcavated, virgin soils farther away from the foundation. Because it is far less compact and has already been disrupted to carve out a bowl in which to build the home, backfill soil absorbs more water and expands far more quickly than the virgin soil that starts 8-10 feet away from your home.

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Backfilled Soils & Virgin Foundation Soils

When your home was being built, contractors had to dig a big hole in the ground. This was created to make space for your basement. They dug up mounds of the hard-packed earth that were there — some of which may have laid there untouched for hundreds of years beforehand.

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. This is known as the clay bowl effect because a clay bowl is carved out from the virgin soil to make room for the house.

The excavation process breaks up and loosens the soil before it is eventually poured back into its original place (or backfilled). Because of this, backfill soils will always be more permeable, or water-absorbent, than the hard-packed earth beyond. When it rains, the water collects in backfilled soils. That water rushes through the soil and presses down in the form of hydrostatic pressure against foundation walls.

Signs of Expansive Soils

Not sure expansive soil is the source of the problem? There are a number of ways to identify that your home may be having issues directly or indirectly related to expansive soils including:

  • Cracks in your foundation or basement walls
  • Sloping or spongy floors
  • Doors and windows that stick
  • Gaps at the top, bottom, or side doors
  • Drywall or stucco cracks
  • A sagging roof
Hydrostatic Pressure

As water builds up in the soils around your foundation, hydrostatic pressure increases against your basement walls, potentially leading to damage.

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:

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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. Eventually, that soil will crumble and erode away. Then, after a heavy rain, that cracked, eroding soil becomes penetrated and oversaturated too quickly with water. Because clay soil absorbs so much water, it expands when wet and contracts when dry.

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, crack, and have its structural integrity severely mitigated.

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Hydrostatic Pressure

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.

Frost Heaving

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. More about foundation heaving. In Georgia, it rarely freezes long enough for frost heaving to occur.

However, when it does freeze outside and then melts quickly after, water can build up and funnel through already-saturated soil too fast. When this happens, it’s the same as having a heavy rain. Hydrostatic pressure builds too quickly and can crack and penetrate your foundation walls.

Do You Need a Foundation Repaired?

When your foundation is showing signs of bowing, buckling walls or any other foundation issues, AquaGuard Foundation Solutions has the knowledgeable and experienced contractors you’re looking for. As a locally owned and operated foundation repair company, we’ve been stabilizing Georgia homes on top of unstable soils for more than 20 years! To put it mildly, with us, you’re in great hands!

We’d like to offer you a free, no obligation foundation repair quote to help you identify the problems you’re facing with your foundation – and what it will take to fix them. To schedule an appointment with one of our certified System Design Specialists, call or e-mail us today!

We’re proud to serve Marietta, Atlanta, Decatur, surrounding areas such as Stone Mountain, Alpharetta, Lawrenceville, Sandy Springs, Athens, Gainesville, Roswell, Norcross, Blue Ridge, Rome, Carrollton, Douglasville, Peachtree City, and everywhere in between!

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