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Expansive Soils

The soils around your foundation can put a lot of pressure on your foundation walls. The effects of these expansive soils on your foundation walls can be cataclysmic if you do not take measures to protect your property.


The soil under and around your property is one of the most important factors in determining the long-term health of the structure of your home. This soil is fundamental, in fact, and provides the surface that the foundation relies on for support. When the soil around your home is healthy, it provides support to your property. When the soil is unstable, loose, or expansive, however, it can fail to provide support or even exert pressure on your foundation and walls. If the pressure exerted is more than your property can handle, this can cause serious and lasting damage to your home as well as lead to a plethora of connected issues as the damage spreads.

diagram of backfilled and virgin foundation soils around a home.

What You Need to Know About Foundation Soils 

Having a grasp of the kind of soil around your home is crucial to understanding potential issues that could affect your home and what kind of preparatory, protective measures you might choose to install. Basement waterproofing, for example, may be a sensible, protective measure to take in very wet and humid climates. 

Broadly speaking, three factors will have a large impact on the amount of pressure that the soil around your home exerts onto your foundation walls. These factors are: 

  • The Type of Soil Around Your Property 

There is no easy way to quickly categorize all soils because the makeup of the earth can vary so widely even within a single county. This is why having a professional soil analysis can do a huge amount of good in the long-run. Generally speaking, however, the levels of clay, silt, peat, loam, and sand in the soil are the most important to your property. In particular, the focus is on how these soils deal with moisture. 

Loam and sand drain fairly well, which makes them non-expansive unless circumstances are extreme. The main weakness of sandy soil is that it can shift and move when water drains through it unless it is very well compacted. This makes it an unstable soil. Clay, peat, or silt-based soils tend to be good at holding water, but they do not drain well. Clay and peat-based soils in particular are incredibly expansive and will expand and shrink based on moisture content. This can lead to excessive pressure on your property in wet seasons and patchy support during droughts. 

  • The Moisture Levels in the Soil Around Your Home 

If there are any underground water sources near your property, they will have a huge effect on the stability of your soil and the pressure your property has to contend with at any given time. Even properties with no nearby water source, however, will face different levels of pressure depending on the weather and season. If you live in an area with heavily clay-based soil, you should be cautious in the wettest months of the year and observe your basement for warning signs. 

  • How Deeply the Foundation Has Been Dug 

The depth of a property’s foundation is calculated depending on the size and weight of the structure as well as the type of soil found in an area. Properties in colder states like Minnesota, North Dakota, and eastern Montana should always have their foundation installed below the frost line, but this is not always the case. If your foundation is on or above the frost line, you could find your property is more susceptible to frost heave. 

These are not the only factors, of course, but they are the most important. You see, your foundation walls are built to withstand pressure from above rather than lateral pressure. This is why soil problems can cause so many issues for your property. When the foundation of your property does not get enough support from below or experiences too much pressure from the sides, it can begin to crack, crumble, buckle, or bow.

The Difference Between Backfilled and Virgin Foundation Soils

Diagram of rainwater affecting foundation soils

Virgin soil, meaning soil that has not been excavated previously for construction, is the most well-compacted and solid soil available. This stability and the self-sustaining moisture regulation that comes with it are created by time, pressure, and complex root systems created by varied plant life which has, over time, bound the soil together. When construction takes place, however, these root systems and the dense compaction caused by pressure are destroyed. When these hard-packed mounds are disrupted to make room for a property’s foundation, they are disturbing soil that may have lain untouched for hundreds of years. 

Once the foundation structures have been constructed, excess earth is backfilled to fill the gaps between the foundation of a property and the undisturbed soil. Of course, contractors do make attempts to compact the backfilled soil once again, but this soil will never be as hard-packed as the undisturbed earth further away from the property. As a result, this soil is more permeable and absorbent than virgin earth and will be more susceptible to expansion and shrinking as a result of saturation and dehydration. This affects the pressure being placed onto your home, it can also cause something known as the ‘clay bowl’ effect.

What Is the Clay Bowl Effect? 

This is a name for what happens when heavy rain saturates backfilled soil, especially newer backfilled soil. The space excavated to make space for a property forms a kind of bowl inside hardier, more compacted virgin soil, both at its sides and below. As a result, water collected by the backfilled soil has nowhere to go or drains very slowly, and the property, in turn, experiences a higher rate of hydrostatic pressure. 

This problem is exacerbated when the property has poorly placed or damaged gutters and downspouts. If your gutter systems are not properly directing water away from your home, the chances of a clay bowl forming are far higher. The most common results of a property existing within a clay bowl are: 

  • Seepage 

Seepage is the result of porous, poured concrete absorbing water in such quantities that it begins to seep through into the basement. 

  • Cracks 

Hydrostatic pressure can cause foundation walls, flooring, and even a property foundation to crack. Wall cracks will allow water to seep into your home. 

  • Bowing Walls 

Bowing walls are a serious problem that is commonly caused by excessive hydrostatic pressure. This issue can lead to other issues, but can also cause walls to collapse in very serious situations.

Expansive Soils


If you notice a curve or lean to your basement walls, you may be very concerned. After all, your basement walls are crucial to maintaining the structure of your property. They are load-bearing walls and so any signs of instability have the possibility of snowballing into damage that poses a real risk of those walls collapsing at some point. Bowing walls can be caused by several issues including: 

  • Foundation Damage 

Foundation damage can be caused by many factors and leads to a generally decreased level of stability in your property. Subsidence, for example, can cause extra pressure to be placed onto certain walls. This extra pressure can cause cracks and crumbling, but buckling or bowing walls are also a very real possibility. 

Another possibility is settlement, which can be caused by expansive soil. Settlement occurs when soil shrinks as a result of dehydration, leaving parts of a foundation unsupported. As a result, sections of a property’s foundation can fall into those gaps. When this happens, the property can, once again, become unstable. Bowing walls are just one possible outcome of this. 

  • Expansive Soil 

Expansive soil is the single most common cause of bowing and damaged walls in a property. This is because of the immense, lateral pressure that expanding soil can put onto your basement walls. While soil saturation can cause serious issues, expansive soil is not solely caused by saturation; it’s to do with the make-up of the soil as well. 

If you have a clay or peat-based soil around your property, you are likely to experience far more lateral pressure against your basement walls and foundation than if you have a loam or sand-based soil. This will be further exacerbated if there are underground water sources near your property. Expansive soil can also damage your foundation and cause heaving under your driveway and patio.

Expansive soil is a kind of soil as opposed to a condition that can be caused in soil. Expansive soils are those which are made of certain kinds of earth. Of course, some conditions are required to cause expansion and contraction and certain conditions can exacerbate these processes and put extra strain on your property. 

  • Clay and Peat 

Expansive soils are those which are primarily made up of moisture-retaining materials like clay and peat. Clay-based soils are undoubtedly the most expansive soils. This is because of the huge capacity of clay to absorb water and the slow rate at which it drains and dries out; when clay is dehydrated, it contracts and can crack. When it is wet, however, it can increase in size by up to a third. 

Peat-based soils, too, retain water very well and expand when they are saturated. However, they expand with slightly less force than clay and have a slightly higher tendency of becoming marshy. This means that while peat-based soils can expand and cause bowing walls, there is also a chance that they will cause subsidence. 

  • Climate and Weather 

Certain areas of the U.S. are more likely to see bowing walls and cracked foundations as a result of the higher proportion of expansive earth in the soils. However, clay-based and peat-based soils can be found all over the country. Those properties that are most harshly affected by expansive soils tend to be those that are also placed in changeable climates. 

Repeated changes in temperature and soil saturation are hugely important to the likelihood that expansive soils will cause damage to a home. This is partly because of how the moisture in soil reacts to temperature (for example freezing). Mostly, however, it is because of the likelihood of fluctuations between severe saturation and dehydration.

Bowing walls are a serious structural issue that could cause larger problems within your home very quickly. As such, the first thing you should do when you notice that your walls are bowing is to call a foundation and basement professional. An expert will be able to not only diagnose the damage but stabilize your property and make it safe before providing a tailored solution. 

  • Mild Bowing 

If your walls have only just started to bow. a professional may suggest minimally invasive measures such as carbon reinforcement or wall braces. Carbon fiber reinforcement strips are only useful for walls that have deviated by less than 2 inches. 

Wall braces are versatile and non-invasive; they will allow you to stabilize damaged walls, but they can also help you to straighten a wall over time. The main downsides of wall braces are that they are very hard to disguise. However, they are also very effective. 

  • Moderate to Severe Bowing 

If you have moderate to severe bowing in some of your basement walls, there is only one solution that will properly stabilize and straighten your walls. Wall anchors are heavy-duty wall repair tools capable of straightening a wall over time. They are, however, easier to disguise than wall braces because the majority of the anchor is placed outside of your property. 

The main downside of wall anchors is the amount of excavation required to install them. Wall anchors require excavation outside of your property for the anchor placement as well as drilling within your basement to feel a steel rod through. The actual wall plates are easy to cover, however, and make adjusting the tension over time very simple.

What Causes Soil to Expand Dramatically? 

All soil expands and contracts to some extent, depending on the temperature, humidity, and amount of moisture in it. Of course, there is more than one potential cause for soil saturation and expansion; these factors can be isolated or combined, but if you have expansive soil putting pressure on your home these are likely at work in some capacity. 

  • Wet Clay or Peat Soil 

Soils that are rich in clay are the most absorbent (though peaty soils come in a close second). As these soils become saturated or dehydrated, they can change dramatically in size, texture, and density. During a drought, this means shrinking, cracking, and crumbling, but after heavy rain, they can expand with huge force, pushing the walls inward. 

  • Hydrostatic Pressure/Underground Water Sources 

Hydrostatic pressure is not just about the saturation of the soil; it is also about subterranean water sources. Saturated soil is, of course, heavy and this weight bears down on your walls along with the pressure of their lateral expansion. Many properties can withstand that, but when you add the weight and pressure of an underground water source, a tipping point is reached. 

  • Frost Heave 

When water turns to ice, it increases in size by almost 10% with a noticeable expansive force. However, when wet soil freezes, the expansive force increases hugely. This can put thousands of pounds of pressure on your property and cause foundation heaving

Whatever causes it, expansive soil can be very destructive to the structure of your home. As a result, properties that are set upon expansive soils should have protecting waterproofing measures installed where possible. If you begin to notice signs of damage, however, you should call a professional quickly; structural damage grows exponentially over time and is easiest (and cheapest) to fix when caught early. 

Call Innovative Basement Authority for Structural Repairs 

If you notice any signs of structural damage, for example buckling or bowing walls, spreading cracks, or sunken sections of concrete, please do not hesitate to contact us immediately. We at Innovative Basement Authority have many years of experience in structural repair and waterproofing to call on as well as a dedicated, skilled, and highly educated team of professionals who are always happy to help. 

We offer free, no-obligation consultation appointments to homeowners in Minnesota, North Dakota, and eastern Montana. These consultative inspection appointments include a same-day, written quote for the cost of our suggested repairs. Our team will never pressure you to make a same-day decision, however, so don’t hesitate to take the time to shop around and explore your options. We want you to feel that you have got the best possible repair solutions and plan!

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We service Minnesota, North Dakota, South Dakota and Eastern Montana for basement waterproofing and crawl space repair.

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