Does Soil Cause Foundation Settlement?

Thursday, March 24th, 2022 by Paige Jackson


What is Foundation Settlement?

Foundation Settlement is the movement your home experiences when the soil below can no longer support its weight. 

 

Causes of Foundation Settlement

The Soil Changed!

 

Your home is resting on many different layers of soil. Each layer under your home is a different soil type and also has its own moisture content. Depending on where you live, the ground may have a completely different composition than other parts of the state. Soils towards the coastline tend to be more sandy and as you move farther inland, the soils tend to be clay-based. 

 

How Water Affects Soil and Your Foundation

Sandy Soils

  • Water passes through sandy soils rather than being absorbed, making them more predictable. Instead of expanding as they absorb moisture and contracting as they dry out, sandy soils maintain a fairly consistent volume and density.
  • Because of their stability and good load-bearing qualities, sandy soils are less likely to shift and settle, so they rarely cause foundation problems.

Clay Soils

  • Soils rich in clay and silt have the greatest potential to damage a foundation. Clay absorbs water easily, expanding in volume as it becomes more saturated. So-called "expansive clays" can cause foundations to crack, heave and shift.
  • When clay soils dry out, they shrink and crack, leaving gaps around a house where water from the next storm can penetrate easily and repeat the expansion cycle. Clay-rich soils can cause more foundation damage by expanding than by contracting.
Heavy rains will cause the soil underneath the foundation to soften
Heavy rains can cause the soil underneath the foundation to soften.
Soft and weak soil will cause a home to sink down, resulting in settlement.

 

Drying & Shrinking of Soil

When we go through a long period of no rain, our soil dries up. A drought can cause clay soil to dry out and when it dries, it shrinks. As the clay soil around your house shrinks in size, it creates empty spaces for your home to settle into. 

 

Foundation soils experience most of their drying and shrinking from two common causes:

Drought: Prolonged dry periods cause the soil to dry out. As we know, when clay dries out, it shrinks. Soil shrinkage beneath a foundation has the same effect as soil settling: It usually causes a section of the foundation to crack and settle into the void or hollow area where settlement has occurred.

Maturing Trees: The root system of a tree can be up to twice the size of the tree's canopy. If a tree's branches extend over your home, there's a good chance that they extend under your house as well, drawing moisture up from the soil and causing it to shrink significantly

Wetting and Softening of Soil

The soils around your foundation experience wetting and softening primarily for two reasons:

Heavy Rain & Flood Conditions: As clay soil gets wet, it holds on to water and becomes very soft. This soft soil can be weak, causing the home to shift.

Poor Drainage: If water is allowed to stand or "pool" next to your home, the soil will absorb the water and swell. As it does, it can lead to bowing walls and cracks in the foundation.

Poorly Compacted Fill Soil

To level a site where a foundation will be built, builders sometimes bring in loose soil from another location to fill depressed or hollow areas. This "fill" soil can be looser than the dense, hard-packed virgin soils at the site that haven't been disturbed - possibly for centuries! The fill soil brought in by the builder has to be compacted thoroughly before a foundation is built on top of it. If the soil is not compacted well, it may begin to compress underneath the weight of your home, creating settlement problems that can damage your foundation.

Does Soil Cause Foundation Settlement? - Image 2
Vertical cracking is caused from an abrupt change
of bearing capacity of the soil.  
This type of crack can be caused from an earthquake or soil washout.
Does Soil Cause Foundation Settlement? - Image 3
Stair-step cracking is a common symptom of foundation settlement. 
This type of crack is normally caused from a loss of bearing over a long period of time.

 

 

 

 

 

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