What Is Backfill in Construction?

All construction work involves some form of excavation.

It may be a shallow hole for the crawl space or a deep one to accommodate a full-depth basement foundation.

Whatever the case, the hole must be filled properly once the footings are constructed and the concrete poured. This is where backfill comes in. 

Backfill Explained 

Backfill is soil used to cover holes or trenches around the foundation. It can be native soil dug out from the ground or a mixture of rocks, stones, and imported soil. Because soils have different properties, each might require different backfilling techniques. 

Backfilling refers to the process of replacing the soil that was removed during the excavation of slabs, foundations, and other groundwork. The process requires heavy equipment, skill, and knowledge of the soil conditions. Soil type, site parameters, and building design all determine the suitability of backfill during construction. 

Methods of Backfilling 

There are a few common methods of backfilling:

• Trench Compaction: An excavator compacts loose material into the trench. Soil is backfilled in layers of four to six inches, depending on the type of compaction equipment used and the nature of the backfill. Water may be added to help with the compaction. 
• Flowable Fill: This method uses a material with a low water-to-cement ratio. Before backfilling, utility pipes are covered with aggregate. The main challenge with flowable fill is its liquidity, requiring containment to prevent it from seeping into other trench areas.
• Water Jetting: Using a probe, pressurized water is added to the bottom of the fill. The force moves the backfill material around. Preventative measures must be taken to contain the sediment-filled water. This method is used for sandy soils or cracked bedrock. 

Backfill & The Clay Bowl Effect

Homes in Missouri often experience the clay bowl effect in wet months. This occurs due to excavation and backfilling during foundation construction.

Key Points:

• Backfill Soil: More porous and absorbent than compacted soil.
• Water Saturation: During snowstorms or heavy rain, backfill absorbs water, pushing against foundation walls.
  • Result: Wall cracks may let water into basements or crawl spaces.
• Heaving: Shallow foundations may heave due to the clay bowl effect.
  • Dry Soil: Trees and plants absorbing excess water can dry out soil, causing voids.
  • Result: Cracked and sinking foundations.
• Deep Foundations: Less likely to heave as they lie below the frost line.
  • Lateral Pressure: Soggy backfill and swelling undisturbed soil can crack mortar joints and cause walls to bow inward or bulge.

Backfilling in 5 Steps

Here’s how builders will backfill the holes around your foundation in five steps:

1. Clean the Area: Remove debris and pump out any stagnating water.
2. Select Materials: Identify the materials to fill the holes and trenches.
3. Layered Filling: Pour the backfill material into the holes in consecutive layers of around 20 cm, starting from the corners.
4. Compact Layers: Compact each layer using a roller or other suitable machinery.
5. Final Compaction: Further compact the layers with steel or wooden log rammers and water them.

Worried About Backfill Issues? Contact Foundation Recovery Systems!

Backfill and associated foundation problems can be complex, but local foundation repair professionals can help you protect your home. Our team at Foundation Recovery Systems is here to assist with any foundation or soil concerns.

Contact us today to schedule a free inspection and repair quote. We’ll assess the situation and recommend steps to keep your home free from leakage and other water-related issues.

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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.