Soil Layers and Types: Preventing Foundation Damage

The soil beneath your home significantly influences the health and sustainability of your foundation. Its composition and water management ability can greatly affect the foundation’s stability.

This article explores how various soil types, backfilling processes, and environmental factors impact your home’s foundation. We’ll also discuss potential problems and available solutions to these issues.

Whether you’re a homeowner seeking to understand more about your property, or an aspiring geologist interested in residential construction, this guide offers valuable insights into soil and foundation dynamics.

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Soil Layers

Understanding the various layers of soil beneath your home is key in the context of foundation stability. These layers, from topsoil to bedrock, each have different characteristics:

1. Topsoil

Topsoil is the uppermost layer of soil, vital for plant life and ecosystem health. Rich in nutrients and organic matter, this layer is crucial for plant growth. Its nutrient richness and moisture retention are due to the decomposition of organic matter, facilitated by bacteria and fungi. While topsoil is vital for supporting plant life and ecosystems, it is not suitable for supporting structures.

Topsoil properties typically include nutrient richness, moisture retention, and varying appearance based on environmental factors. It plays a significant role in gardening. The formation of one inch of fertile topsoil takes about 1,000 years, highlighting the need to protect it from removal, pollution, and disruptive practices such as excessive use of herbicides and pesticides. Sustainable land management is critical for preserving this resource.

2. Subsoil

Subsoil, found beneath topsoil, contains minerals and is influenced by water movement. Although it’s rich in minerals, it lacks the organic matter abundance found in topsoil. Water movement transfers minerals from the topsoil to the subsoil via runoff.

The accumulation of clay in the subsoil encourages deeper root growth in plants, as they seek nutrients and secure anchorage. The color of subsoil varies, often displaying red and yellow hues.

3. Bedrock

Bedrock offers excellent support for structures due to its strength and stability. When the surface soil is insufficient to support a structure, deep foundations that extend to the bedrock are used. This helps to reduce the risk of shifting.

For homes built on unstable soil or exhibiting signs of foundation damage, foundation piers can be installed. These steel rods reach down to the bedrock to transfer the building’s weight to it.

However, reaching bedrock may not always be feasible due to its depth or the associated costs. Thus, the choice of foundation depends on the type of structure, soil properties, and budget.

4. Man-Made Soil Layers:

Construction involves the use of both natural and man-made soil layers.

Engineered Backfill Soil: This type of soil is used to replace non-engineered types, supporting foundations in even unsuitable locations (discussed in more detail later).
Dumped Fills: These are used to cover landfills and are re-engineered for foundations.
Hydraulic Fills: This multi-layered soil comes from water bodies and is used to elevate land and replace native soil.

While builders take into account soil conditions, weather, and use frequency, it is important to examine the soil beforehand to prevent structural problems. If you have any concerns about your home’s soil and foundation, it’s advisable to consult an expert.

Soil Types: Stable Vs. Unstable

The type of soil is critical to the stability and durability of a foundation. Various soil characteristics define its suitability for construction.

Good soil is stable under different conditions, can withstand pressure, and efficiently drains water.
Unstable soil may lead to foundation problems like cracks, sinking, and possible failure.

1. Clay Soil (Moderately Stable, but Expansive):

Clay soil, derived from shale, is known for holding water and being sticky when wet. While generally strong soil type, it poses problems for foundations due to its water retention. To manage this, builders sometimes mix clay with gravel.

Clay swells when wet and shrinks when dry, which is a major issue in the U.S. due to minerals like bentonite and vermiculite in certain regions. When the soil expands, it puts pressure on the foundation, causing damage both inside and outside the home.

2. Sandy Soil (Unstable):

Characterized by larger particles, sandy soil does not significantly swell or shrink with moisture changes, but it can be prone to erosion, which can destabilize foundations over time.

While sandy soil doesn’t shrink or swell like clay, it’s prone to erosion. Without proper drainage, sandy soil can erode over time, compromising the foundation’s support.

3. Rock Soil (Stable):

Consisting of solid rock, it is inert and doesn’t react to moisture, making it stable and ideal for foundations.

4. Loam Soil (Relatively Stable):

A mix of sand, silt, and clay, loam soil combines the beneficial traits of its components. However, it can be prone to erosion due to its sand content, potentially compromising foundation support.

Although loam soil holds moisture well and has good drainage, its sand content makes it susceptible to erosion. Consequently, it may not provide adequate support for foundations.

5. Shale (Unstable):

A sedimentary rock with quartz, clay, and other minerals. Like clay soil, it can swell when wet and shrink when dry, causing instability and potential foundation damage.

Shale contains clay minerals, making it susceptible to shrinking and swelling with changes in moisture levels. Similar to clay soil, these changes can damage the foundation.

6. Soils with High Organic Content (Very Unstable)

Soils with high organic content, like peat, are also unsuitable for foundations due to their compressibility and tendency to decompose. It has a general character of spongy swampiness.

Backfill: The Soil Around Your Foundation

Backfill soil is a crucial component in the home construction process. It is the soil excavated from the site where the foundation is laid, then returned and compacted around the foundation after construction.

This process fills the spaces between the earth and the foundation, reinforcing the soil’s stability, crucial for supporting the structure’s weight. It also significantly contributes to your home’s insulation and drainage

Types of Backfill Materials

Coarse-Grained Soil: This soil type, typically a gravel, sand, and fine materials mix, is commonly used for backfill. Its low plasticity and excellent compaction properties make it suitable for supporting the foundation.
Fine-Grained Soil: Although this soil type has smaller particles, it generally has inferior drainage characteristics. However, once compacted, it can provide robust support to the foundation.
Commercial By-Products: Products like furnace slag can be used as backfill, particularly when the existing soil needs enhancement.

The Importance of Backfill Compaction for Your Foundation

The compaction of backfill soil is critical for foundation stability as it increases the soil’s density and load-bearing capacity, reduces air pockets, and prevents movement. Compaction, usually done in 20 cm thick layers, also improves drainage by directing water away from the foundation, thus preventing water damage.

The choice of backfill material and compaction method (including machine compaction, water jetting, and/or flow filling) are both essential for successful compaction and optimal drainage. Despite thorough compaction, backfill soil remains less dense than undisturbed native soil, leading to a phenomenon known as the “Clay Bowl Effect”.

If the condition of various soil layers and types begins to deteriorate, your home might face the following issues:

Bowing and Buckling of Foundation Walls: Expanding clay soil can exert pressure, causing foundation walls to bow inward or buckle.
Foundation Cracks and Damage: Swelling soils can cause cracks in foundation walls and floors. During dry periods, the loss of support can lead to settlement and further structural deformation. Additionally, the shifting of clay soil can place stress on the foundation, resulting in cracks.
Secondary Issues: Cracks and fissures in the foundation, caused by expansive soils, can allow water to seep into crawl spaces and basements. This can lead to mold growth, wood rot, and water damage.
Other Visible Signs: Expansive soils often display noticeable symptoms, including sloping or sagging floors, sticking doors and windows, gaps around doors, and curved or sagging roofs.

1. The “Clay Bowl Effect”

The “Clay Bowl Effect” describes a situation where backfilled soil around a foundation, being less dense than the undisturbed soil it replaces, forms a bowl-shaped area that retains more water.

This excess water creates a “false water table”, increasing hydrostatic pressure on the foundation, and potentially leading to settlement issues.

2. Landscaping Issues: Negative Yard Grading

Yard grading refers to the slope or incline of the land around your house. It’s crucial for directing water flow to protect your foundation from water damage. There are two types of grading:

Positive Grading: Your home is at the highest point of your yard, ensuring water naturally flows away from the foundation and basement, thus reducing the risk of water damage.
Negative Grading: Your home is located at a low point, or the lowest point, of your yard, causing water to flow towards your foundation. This can result in foundation problems such as basement leaks, foundation cracks, and bowing basement walls.

Here are some signs of negative grading:

Spongy Soil: If your soil feels overly soft and water seeps up when you step on it, this indicates water saturation.
Basement Leaks: Negative grading increases the chances of basement water damage.
Mosquito Infestation: Poor drainage and standing water attract mosquitoes.
Dying Grass: Excessive water can rot grass roots.
Dying Landscaping: Soggy soil makes it challenging to maintain healthy landscaping.

If your yard has poor grading, consider consulting a landscaping professional or a foundation expert to evaluate the situation and implement suitable solutions.

3. Foundation Settlement

Different types of soil affect foundations in various ways. None are completely resistant to settlement, which occurs when the soil beneath a building shifts, compresses, or sinks.

This can cause parts of your home to sink lower than others, leading to noticeable structural problems. This is primarily due to unstable soil, drainage issues, erosion, and poor compaction.

Repair & Prevention Methods

To mitigate the effects of the mentioned issues, several strategies can be employed:

1. Exterior Drainage

Gutters and Downspouts: Make sure gutters are level and downspouts drain water away from the foundation.
Yard Drains and Catch Basins: Install these in lower yard areas to divert excess water away from the foundation.
Yard Regrading: Adjust the yard’s slope to direct water away from the foundation.
Proper Planting/Replanting: Strategically place plants to balance water absorption and avoid foundation risks by keeping flowers within five feet and large trees within 20 feet.

2. Interior Drainage

Interior drain installed along a basement wall.

Interior Drains: These are installed along the interior perimeter of the basement to collect and redirect water away from the foundation.
Sump Pumps: These are used to pump out accumulated water from the basement or crawl space, preventing water damage and maintaining a dry environment.

3. Wall Reinforcement

Wall anchor on a concrete basement wall.

Steel I-Beams: These are employed to offer extra support to foundation walls. Often, they are installed vertically against the wall to counteract inward movement caused by soil pressure.
Carbon Fiber Wall Repair: This method involves applying carbon fiber strips to foundation walls to inhibit further bowing or cracking. Despite being lightweight, it’s a highly durable solution.
Crawl Space Support Jacks: These adjustable steel posts are installed in your crawl space to provide added support, preventing sagging or bouncing floors above.

4. Foundation Piers

Push pier installed on the footing of a home.

Foundation piers bypass unstable soil layers to transfer a structure’s weight to either bedrock or a stable soil layer. A professional inspection can identify the specific soil layers beneath your home, which may differ based on location.

There are three main types of foundation piers, each designed for different situations:

Push Piers: Hydraulically driven into the ground, these piers utilize the weight of the structure to reach load-bearing strata. Perfect for heavier buildings.
Helical Piers: Resembling large screws, these piers are twisted into the ground using a hydraulic torque motor. Their helical plates provide strong anchoring, making them suitable for various soil conditions and structures of different weights.
Slab Piers: Designed specifically for slab-on-grade foundations, these piers lift and support the concrete slab, addressing issues like cracking and uneven floors caused by settlement.

Choosing the right type of pier depends on factors such as the structure’s weight, soil conditions, and the extent of the settlement. A qualified foundation repair expert can assess your particular situation and recommend the most effective solution to ensure your home’s long-term stability.

Contact Foundation Systems of Michigan Today!

Knowing the type of soil under your home is important for keeping the foundation strong. Different soils, like clay or sand, can cause different problems.

You can prevent these with good building methods, proper drainage, and extra support for the foundation. Contact professional contractors at FSM and schedule a free inspection and repair estimate.

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Soil Layers and Types FAQs

What role does soil type play in causing foundation cracks?

Different soil types, such as expansive clay or poorly compacted soil, can exert pressure on foundation walls and contribute to cracks. Understanding your soil’s characteristics helps in devising effective repair strategies.

How Can I Prevent Soil Erosion?

Preventing soil erosion starts with effective landscaping techniques and moves to proper drainage systems. By combining these methods, you can significantly reduce soil erosion and protect your property’s structural integrity.

Will Replacing the Soil Work?

Now that you know that problem lies in your soil, and not the concrete, you may be wondering whether replacing the sandy, loose soil in your yard with more stable soil is a good option. In theory, it may sound like a good idea, but in reality, it has too many downsides. Let’s check them out.

Why Replacing Your Soil Won’t Work

If you have done your research, you may have found that loam soil is very stable. It is a combination of sand, silt, and clay, so it doesn’t shrink and expand like clay soil nor does it shift easily like sand. This mix is the best of all worlds and is frequently used in farming. However, it is not often used in landscaping, and there are good reasons for that.

First of all, replacing the soil in your yard with loam can be really expensive. In addition, this soil is mostly used in fields where water exposure is closely monitored. When you live in Michigan where heavy rainfalls and floods are nothing unusual, large streams of water can still wash out loam soil, and with it all your money and hard work.

A Better Solution

If you are dealing with soil washout, contact Foundation Systems of Michigan and see what your options are regarding waterproofing your yard, drainage, and foundation and slab repair. Investing in such solutions can give you peace of mind and even increase the market value of your property.

Solving the problems caused by soil washout over and over again is a lot harder than just trying to avert the problem altogether. Keep your eyes open for signs of erosion and take action before things start to get worse.

Leah Leitow

Content Writer

Leah is a Content Writer for Groundworks with nearly ten years of experience working in the foundation repair industry. Her experience ranges from working with homeowners to find the right solution to training inspectors and staff. In her background as a Michigan journalist, she gained invaluable insight into people's lives throughout our state. Leah lives in metro Detroit with her husband and two sons.