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Learn everything you need to know about backfilling, what materials are used, and why it's so important for a stable foundation.
Published 22 Nov 2022
Backfilling is the process of filling in the excavated area around a foundation or structure. The backfill material can be anything from soil to gravel and is usually compacted to provide support and stability. Backfill can also be used to insulate foundations or improve drainage. Backfilling is essential in the construction process, following the foundation's pouring and installing utility lines.
Depending on the project, backfilling can be a simple or complex operation requiring special equipment. It is vital to ensure that the backfill material is compacted correctly to provide a stable foundation.
Several factors need to be considered when backfilling a foundation. Below are some of the most critical factors:
The backfill material must be appropriate for the job. Soil, sand, gravel, and crushed stone are all common backfill materials. The type of material will vary depending on the application. As an example, crushed stone can improve drainage around foundations.
The backfill material must be appropriately compacted to provide a stable foundation. Hand tampers, plate compactors, or roller compactors can be used for this process. The equipment used for compacting differs based on the material’s size and type.
The backfill material must be placed in the excavation layers and compacted after adding each layer. Depending on the material, each layer will have a different thickness.
Generally, the soil should be placed in layers 6 to 12-inch-thick and compacted with a hand tamper or plate compactor. Gravel and sand can be placed in 3 to 6-inch-thick layers and compacted with a hand tamper or roller compactor. The crushed stone should be placed in 2 to 4-inch-thick layers and compacted with a hand tamper or plate compactor.
Eliminate manual tasks and streamline your operations.
Based on the type of material used, backfilling can be classified into the following types:
Coarse-grained soils include gravelly and sandy soil types and clayey sands through gravel-sand mixtures with little or no fines. These soils are relatively easy to compact.
Organic clays of low to medium plasticity (such as gravelly, sandy, or silty clays and lean clays), silts (including organic and inorganic silts), and fine sands (such as silty fine sands or clayey silts) are all examples of fine-grained soil.
Using commercial by-products, such as furnace slag or fly ash as backfill material, may be desirable when natural materials are unavailable. Fly ash can be used as a lightweight backfill behind a 25-foot-high wall. It can also be mixed with clay to make it more plastic.
The suitability of these materials depends on how well they meet the foundation’s needs and the products’ engineering characteristics.
CLSM is a cementitious material used as backfill, void fill, and utility bedding. Fly ash, cement, and other similar products make up the mixture. The fly ash mixture can come from thermal power plants.
The main difference between filling and backfilling is that filling adds new material to an excavation while backfilling is the process of refilling an excavation. Backfilling is usually done at the end of a construction project, while the filling is often done throughout the project to keep the excavation stable.
Backfilling happens after the foundation has been constructed and the concrete has had time to cure. This process usually takes 5-7 days after pouring the concrete. The backfill process helps to ensure that your property has a sturdy foundation by filling in any voids around the perimeter of the foundation.
The coarse-grained soil is the most popular option. It is a blend of gravel, sandy soil, and just enough fine materials. You want soil that will allow for proper drainage and will not expand or contract too much with changes in moisture. Because it offers excellent foundation support while being easily compacted, this is a high-quality backfill.
Backfill must be deposited in horizontal layers that are no more than 200 mm thick. Before adding the next layer, each layer should be tamped down and compacted using mechanical tampers. The layers should be as level as possible to promote even compaction.
Using a multi-purpose inspection app like SafetyCulture (formerly iAuditor) can simplify the backfilling process by providing a checklist of things to check. This platform also offers solutions to keep your workers and the construction site safe during backfilling operations. With SafetyCulture, you can:
Rob Paredes
Rob Paredes is a content contributor for SafetyCulture. He is a content writer who also does copy for websites, sales pages, and landing pages. Rob worked as a financial advisor, a freelance copywriter, and a Network Engineer for more than a decade before joining SafetyCulture. He got interested in writing because of the influence of his friends; aside from writing, he has an interest in personal finance, dogs, and collecting Allen Iverson cards.
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