Just when everyone thought winter was over, Minnesotan’s got slammed with over 18 inches of snow! April never fails to keep us on our toes.
As you know, snowy winters like these can cause various problems on properties, particularly with retaining walls.
Today, we will be discussing how the winter season can affect boulder retaining walls if a proper water management system is not in effect.
*Boulder Wall Failure
What Makes a Retaining Wall Structurally Sound
A structurally sound retaining wall isn’t just stacked stone, it’s an engineered system that manages soil pressure, drainage, and environmental loads. Proper retaining wall engineering design includes:
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Soil Pressure Management: Walls must be designed to resist lateral earth pressure. The taller the wall, the more force it must withstand.
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Base Preparation: A stable base layer distributes loads evenly. Footings must be set below frost depth to prevent shifting during freeze-thaw cycles.
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Engineered Backfill: Compacted aggregate backfill reduces pressure and allows for drainage.
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Drainage Design: Without proper drainage, water can build up behind the wall and create hydrostatic pressure, leading to cracking or collapse.
Even small residential walls need the right engineering. Most Minnesota municipalities require stamped plans for any retaining wall over four feet tall.
Common Causes of Retaining Wall Failure
Retaining walls don’t fail overnight—it happens gradually due to overlooked design or environmental factors. The most common causes include:
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Poor Drainage: Trapped water increases lateral pressure and weakens the wall structure.
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Frost Heave: Moisture in the soil expands as it freezes, shifting the base and creating cracks or tilting.
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Under-Engineered Bases: A shallow or uneven footing can cause the wall to settle or lean over time.
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Improper Backfill: Using clay or organic soils that retain water accelerates deterioration.
When these problems combine, you can end up with leaning walls, cracked stones, or total failure.
Learn more about related services:
Storm Damage Restoration
Foundation Engineering
First, we want to make it known that there are several codes applicable to retaining walls. Most municipalities require an engineer to design any retaining wall that is over 4 feet tall. With this being said, we want to touch on a few factors homeowners should be aware of when inspecting their existing retaining wall or when building a new one:
Water Management:
When water is allowed to infiltrate your retaining wall, it can actually cause settling and degradation. To avoid this, there are certain systems that must be included and implemented into your retaining wall design.
*Photo Credit: City of Sparks Community Development Department
Backfill:
Every newly built retaining wall has back fill soils that are put behind and/or below the wall and are compacted during construction. The type of soil selected is very important and often forgotten. For instance, Minnesota is comprised of organic and alluvial clay soils that retain water. Soils that retain water will be a nightmare when it comes to the preservation of your retaining wall. If these soils are existing on your property, you will want to remove them and use soils that do not retain water such as compactable aggregate soils. This could be anything from recycled asphalt and concrete (con-bit), to red rock gravel, or equivalent.
Drain bed:
In between the boulder wall and the backfill soil, there should be a drain bed. The drain bed is meant to invite water to enter so it can be directed behind the retaining wall and routed via PVC out the sides of the boulder wall laterally or out the front of the boulder wall through water exits. Appropriate drain bed soils can be washed aggregates or washed river gravel. Sand is not a good choice because it will just wash out.
Solutions for wet “swampy” land:
If your property is located on swampland or land with consistently wet soils, you will need to implement a system to prevent movement underneath the boulder wall itself. Because the soils are wet, a traditional footing won’t work. One such solution we have found to be very successful is the implementation of geo-fabric layers and conbit in an s-shaped form. To learn more about this specific system, feel free to give us a call.
*Boulder Wall Failure
Boulder vs. Concrete Retaining Walls in Minnesota
Both boulder and concrete retaining walls are common in Minnesota, but they perform differently depending on the site conditions and engineering needs.
| Type | Pros | Cons |
|---|---|---|
| Boulder Retaining Wall | Natural appearance, good drainage, flexible design for uneven terrain | Requires larger footprint, heavy equipment for installation |
| Concrete Retaining Wall | Strong and space-efficient, allows for engineered reinforcement | Prone to cracking without proper drainage or footing depth |
Boulder walls are especially popular around lakes, slopes, and properties where aesthetics matter. Concrete walls are better suited for small yards or where space is limited.
Both types must be engineered correctly to withstand freeze-thaw cycles and soil movement.
Engineering Retaining Walls for Minnesota Weather
Minnesota’s climate poses unique challenges. Between snow loads, freeze-thaw cycles, and clay-heavy soils, retaining walls here face more stress than in most regions.
To protect against damage, our engineers design retaining walls to handle:
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Frost Depth Requirements: Footings extend below the frost line to prevent seasonal shifting.
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Drainage During Snowmelt: Systems are designed to channel meltwater safely away from the wall base.
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Soil Type Considerations: Alluvial and organic clays common in Minnesota retain moisture and require replacement with compactable aggregate soils.
This is especially critical for properties on slopes or near wetlands. The combination of melting snow and saturated soil can quickly compromise a wall’s structure.
How CBSMN Engineers Design for Long-Term Stability
At Complete Building Solutions, we combine engineering expertise with local knowledge to ensure retaining walls remain stable year after year.
Our design process includes:
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Site Evaluation: We assess soil composition, slope, and drainage.
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Custom Engineering Plans: Walls are designed to meet local code requirements and long-term performance standards.
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Material Selection: We help clients choose between boulder, concrete, or hybrid systems depending on soil conditions.
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Inspection & Maintenance: We provide post-construction evaluations to ensure continued structural integrity.
If you’re planning a new wall or have concerns about an existing one, schedule an inspection to prevent costly future repairs.
Water Management and Drainage Design
When water seeps into a retaining wall, it can cause the soil behind it to settle and the structure to weaken over time.
Every properly engineered retaining wall should include a drainage system that directs moisture away from the wall to prevent damage.
A typical drainage setup includes a layer of washed gravel or aggregate behind the wall, perforated PVC piping to move water laterally, and drain outlets that allow moisture to escape safely.
Avoid using sand as backfill since it can wash out over time, leaving gaps and voids that compromise the wall’s stability.
Backfill and Base Preparation
A strong retaining wall begins with engineered backfill and a compacted base.
Minnesota’s natural clay and organic soils tend to hold water, which adds unwanted pressure behind the wall.
Using the right materials, such as recycled concrete, red rock gravel, or con-bit, helps create a stable foundation and improves drainage performance.
Solutions for Wet or Swampy Land
Properties built on saturated or swampy ground require extra stabilization since traditional footings can shift or sink in wet soil.
We often use a combination of geo-fabric layers and con-bit arranged in an “S-shaped” pattern.
This system helps disperse weight evenly and prevents movement underneath the wall.
Wrapping Up Structurally Sound Retaining Wall
Overall, water needs to be directed away from the retaining wall. As the snow melts this season, be sure to inspect your wall. Do you notice pooling water, settlement, or degradation? If so, call Complete Building Solutions so we can help you create a solution that may help your retaining wall perform and last the way it is meant to.
612-868-2922
FAQs
How deep should a retaining wall footing be in Minnesota?
Footings should extend below the frost line, typically 42 to 60 inches deep to prevent frost heave and shifting during freeze-thaw cycles.
What type of engineer designs retaining walls?
A structural or civil engineer designs retaining walls to handle lateral soil pressure, drainage, and site-specific loads.
Do retaining walls need drainage?
Absolutely. Without drainage, water builds up behind the wall, increasing hydrostatic pressure that leads to cracking or collapse.
Sources:
Source: City of Sparks Community Development Department. “Prescriptive Standards for Design, Installation and Inspection of Rockeries.” Http://Cityofsparks.us/, cityofsparks.us/wp-content/uploads/2017/01/cs-eng-prescriptive-standards-for-rockerywalls.pdf.
