What Is Backfilling in Construction?

Backfill soil is an important factor in the health of your foundation. If you’re experiencing foundation issues, having a basic understanding of what backfill is in construction can help you determine the proper methods for repair. It can help you figure out what exactly a given foundation repair expert is proposing to do around your home and provide you with questions you can ask them to thoroughly vet their expertise.

At FSM, we pride ourselves in preparing against every little environmental factor that could be causing your foundation issues. We think it’s really helpful to give you a conceptual frame of reference on technical aspects of our work in order to help you understand exactly what needs to happen to get your home back on solid ground.

Schedule Free Inspection

In Construction Terms, What Is Backfilling?

“Backfilling” in construction refers to the process of adding and compacting soil, gravel, and/or other commercial refill products into the excavated site around your home’s foundation after the foundation footings have been laid.

After a construction crew pours the concrete for the foundation, there will be gaps and holes left around the substructure that will need filling up.

The Importance of Backfilling

Here’s why:

Support: First and foremost, backfilling provides structural support. By filling the spaces around the foundation, it helps to uphold the weight of the structure and prevent any shift or movement that could compromise its stability.
Insulation: Backfilling plays a role in thermal insulation. The soil used in backfilling can act as a barrier that keeps out extreme temperatures, contributing to the energy efficiency of the structure.
Drainage: Proper backfilling also ensures proper drainage. It can help direct water away from the foundation, thus preventing any water damage or weakening of the structure due to moisture build-up.
Visuals: Lastly, backfilling is key to site restoration. After the construction is finished, backfilling helps to return the site to its original level, making it safe and usable again.

In short, backfilling is an integral part of construction that greatly affects the long-term safety and durability of a structure.

The Steps of the Backfilling Process

Here is a step-by-step guide on the backfilling process:

Excavation and Site Preparation: The first step of backfilling is preparing the site. This involves excavating the area around the foundation where the foundation will be laid down, and after which the backfill material will be placed. All debris, stones and roots must be removed to ensure a clean and level surface.
Foundation Concrete Pouring: The concrete footings for the foundation are poured with reinforcement into the excavated soil.
7-Day Waiting Period: Before backfilling, the foundation needs time to cure adequately. This waiting period depends on the type of foundation and the concrete mix used. The general rule is to wait at least seven days before starting the backfill process.
Material Selection: Choose the right backfill material, considering factors such as soil type, moisture content, and the specific requirements of the project. This could vary from using the soil originally removed during excavation to using a mixture of sand, gravel, or other commercial refill products.
Material Placement: The chosen backfill material is subsequently placed into the excavated area. Construction professionals aim for a uniform distribution when placing the backfill. This process involves adding the material in layers, typically of 20 cm, starting from the bottom and working upwards. This method helps prevent uneven pressure on the foundation walls. It’s a repetitive process that involves incremental filling and compacting.
Layer Compaction: Each layer of backfill material is compacted to ensure a stable and solid foundation. This could involve using a roller or other machinery to compress the soil and remove any air pockets.
Final Grading: After the backfilling process is complete, the area is graded to ensure proper drainage away from the foundation. This involves shaping the land to create a slope that directs water away from the building.

Each of these steps plays a crucial role in achieving a stable foundation and ensuring the long-term safety and durability of the structure.

A well-executed backfill process is crucial for the long-term stability of your foundation. Always consult a professional to ensure the backfill is done correctly.

How Long Does Backfilling Take?

Typically, after the foundation is poured and allowed to cure for 7 days, the rest of the backfilling process should only take 1-2 days because layers are compacted gradually. But the exact duration of the backfilling process can vary based on a number of factors such as the size of the foundation, the type of soil, and the specific requirements of the project.

Equipment, Methods, and Materials

Backfilling Equipment

Backfilling requires the use of heavy machinery for excavating and compacting the soil.

Excavation comes first. For this, most pros rely on a combination of the following:

Excavators: Used for digging and removing soil from the foundation site. They’re ideal for preparing the site for backfilling due to their capacity to lift out large amounts of soil.
Trenchers: Specialized equipment for digging trenches, particularly for laying pipes or cables. They’re essential for projects requiring precise excavation work.
Loaders: Used for lifting and transporting backfill materials out of and back into the the excavation site.

After the foundation has been laid, it’s time to compact it. To do this, most builders use different compacting equipment for different soil types. These may include:

Rammers (AKA “Tampers”): Effective for compacting cohesive soils like clay and silt due to their high impact force. They’re ideal for compacting thick layers of soil.
Plate Compactors: Suitable for compacting granular soils like sand and gravel, and thin layers of cohesive soil. They provide rapid impacts to the soil surface for effective compaction.
Roller Compactors: Used for large-scale projects or when a significant volume of soil needs compaction. They work well on all soil types, especially non-cohesive soils.

Backfilling Methods

The technique used for backfilling is important for foundations stability. It needs to ensure uniform compaction to avoid creating pressure points that can cause cracking in the near future.

Common backfilling methods include:

Compacting: This prevalent method involves adding backfill material in layers and compacting each one with machinery. It’s suitable for most types of backfill materials, especially coarse-grained soils.
Water Jetting: This approach uses a high-pressure water jet to compact the backfill material. It’s typically used with fine-grained soils that are challenging to compact using traditional methods.
Filling with Flowable Fill Concrete: This method uses flowable fill concrete as the backfill material. This type of concrete easily flows into all spaces, providing uniform support. It’s often used for utility trenches or other structures requiring strong, consistent support.
Dumping: This straightforward method involves simply dumping the backfill material into the excavation. This method is typically used for non-structural backfill where compaction is unnecessary.

Each method is chosen based on specific project requirements and the type of backfill material.

Backfilling Material Types

Choosing the right backfill material is important. If builders choose the wrong material, homeowners like you might have problems with compaction and drainage. Both can make the foundation less stable over time.

Here are some of the backfill materials you can use in your construction project:

Coarse-grained soil: This is a mixture of gravel and sandy soil with a small amount of fine materials. It offers strong support for the foundation and compacts well.
Limestone screenings: These compact well and are often used for backfilling sewers and pipes. Some builders use limestone screenings as a base for brick paving.
CA7 bedding stone: This is a self-compacting material that is widely used in construction. It is ideal for bedding pipes, subbase work, and improving soil drainage.
CA6 base stone: This is another popular option in construction and is used in both commercial and residential projects.
Trench backfill: This backfill material consists of small aggregates and is known for its good drainage and compaction properties.
3” coarse stones: These are recommended for large holes and trenches. They should be used as the first layer and covered with another material like CA6 base stone for compaction.
Commercial by-products: Depending on the quality of the soil around your property, builders may have used commercial by-products like fly ash to improve soil quality for backfilling.

If you’re seeing foundation issues like settlement, then understanding what type of material was used to backfill the soil around your foundation can help a repair expert account for the unique factors putting pressure on your foundation and apply better-optimized repair solution.

Impact of Backfilling on Foundation Stability: The “Clay Bowl Effect”

Backfilling is done in order to help prevent foundation settlement. However, this process causes the “Clay Bowl Effect.” No matter how well-compacted the soil around your foundation is, it will still be less dense than the original soil. This means that the more permeable backfill soil will create a false water table and collect water near your foundation, putting more hydrostatic pressure on it than around other areas of your property—and that’s how you get settlement.

What can you do about this? First, monitor the backfill’s moisture content and implement drainage systems that can help maintain optimal moisture for stability. Another thing you can do to prevent damage is to have foundation piers installed that go all the way down to load-bearing strata to permanently stabilize your foundation.

If you’re seeing signs of foundation damage, it’s really important to call a foundation repair pro who can help fix the problem fast.

The Environmental Impact of Backfilling

Backfilling in construction can have a significant impact on the environment, especially if done wrong. Considerations for the environment should include:

Soil Erosion: Using erosion-resistant backfill materials limits soil disruption, decreasing harm to ecosystems and water pollution. Erosion-prone materials like sandy soils can enhance soil erosion and cause water pollution.
Water Infiltration: Good drainage is important in backfilling. Materials that block proper water infiltration can result in waterlogged soils, endangering local plants and increasing flood risks. Conversely, materials promoting too much water infiltration can dry out the soil, harming local plants.
Environmental Footprint: The type of backfill material affects the total environmental footprint of a construction project. Using locally-sourced or recycled materials and fuel-efficient machinery can lessen this impact. Consider the environmental effects of extracting, processing, and transporting backfill materials.
Compaction: Wrong selection and compaction of backfill materials can cause environmental problems. Poor compaction can lead to excess water gathering around the foundation, which can waterlog the soil and encourage mold and mildew growth. Over-compacted soil can block water infiltration, increasing runoff and potential flooding.
Sustainability: Using non-sustainable backfill materials can increase the environmental footprint of construction projects. For instance, extracting and transporting non-renewable resources for backfill can lead to high carbon emissions.

If you have questions about any of this in regard to the soil around your foundation, feel free to call us or schedule a free inspection. We’ll be happy to find dig deeper into how your foundation soil is impacting the local ecosystem.

Think Your Backfill Is Causing Foundation Issues? Call Us Today!

Concerned about the backfilling of your foundation walls during construction? Schedule a free inspection and repair estimate with the FSM experts. We serve Detroit, Grand Rapids, Traverse City, and areas in Michigan. With us, you can repair any foundation damage from backfilling easily. As these issues can pose safety risks, it’s crucial to address them immediately.

Don’t wait! Call us today!

SCHEDULE FREE INSPECTION

FAQs

Is concrete leveling a long-term solution?

Yes, concrete leveling, especially when done using polyurethane foam injection, is a long-term solution to most concrete problems. This method not only raises and levels the concrete but also stabilizes the soil beneath, reducing the likelihood of future settling. However, the longevity of the repair can also depend on addressing the underlying issues that caused the unevenness, such as improving drainage around the driveway.

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.

Is it safe to live in a house with foundation settlement?

Minor settlement is usually not a safety concern. However, significant or uneven settlement can lead to structural issues that may make it unsafe to live in the home until repairs are completed.

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.