Builders often do a lot of digging and excavation work to create clean and level grounds to lay the foundation on. After erecting the foundation walls, the gaps left are filled to prevent future water problems. Most builders use the natural soil already on the property to fill these gaps while others opt to use alternative backfill material. Here, we define backfill soil, its purpose, and the different types of backfill material.
What Is Backfill?
Backfill is the material used to refill an excavated hole or trench in your yard. This material can be the excavated soil, a mixture of sand and gravel, or commercial products. The process of backfilling usually takes place in layers. Different materials have different properties. Some are small while others are big.
Why Backfill Around the Foundation?
Backfilling is usually done to firm up the foundation. On top of this, it also promotes better water drainage and helps avert hydrostatic pressure. To get the best outcome, take the time to understand which fill material is best for your project, how to compact it, and how long the process should take.
Types of Backfill Material
Whether you’re constructing a foundation wall, retaining wall, or working on a landscaping project, you have to consider the type of backfill that suits your project. This depends on your drainage needs and the scope of your project. Here are some popular backfill materials.
Trench backfill: This material consists of small stones like aggregate that allow water to escape. It is easy to compact.
Limestone screenings: This type of backfill compacts well and is suitable for use as sewer and pipe backfill. Some builders also use it as a base for brick paving.
Coarse-grained soil: This is standard backfill material in home construction. It contains sand, gravel, and small amounts of fine materials. This backfill provides ample support for your foundation and is easy to tamp down.
CA7 bedding stone: This backfill material comprises a white/gray stone that self-compacts. It is ideal for projects where drainage is necessary. This backfill material is also frequently used in the construction of pipe bedding and subbase.
CA6 base stone: This is a subbase granular backfill that is often used as a road base or along roadway shoulders. Some builders use it as backfill for residential projects.
3” coarse stones: Large holes in your yard ought to be filled with 3” stones as they have excellent drainage properties. Such stones usually form the base layer of the backfill. After the trench is filled, a CA6 base stone is placed on top before compaction starts.
Commercial by-products: Furnace slag and fly ash come in handy in situations where suitable natural backfill doesn’t exist. What type of backfill you’ll use depends on the soil condition and the desired engineering properties.
How to Backfill Your Foundation
While contractors approach backfilling differently, the steps in the process remain pretty much the same. Here’s the typical process:
- Standing water is first removed from the construction site.
- You get to choose the right backfill material for your project based on the existing conditions of your site.
- The trench is backfilled with your preferred material in layers of 6” to 8”.
- Each refill layer is compacted with a roller or any suitable machine until the backfill is firm before the next layer is poured.
- Finally, the backfill is watered thoroughly.
Compact the Backfill
No matter how many layers of backfill you create, the soil on your trenches is still going to be loose. This soil needs to be tamped down as it can get soggy in rainy weather. Within no time, water will start pushing out and against your foundation. This outward force will cause your walls to crack or bow. You can avoid this scenario by ensuring the refill material is compacted properly.
Before you pour the backfill in the foundation holes, you’d want to make sure the foundation walls have adequate waterproofing. Complete Basement Systems can help you install interior waterproofing measures so your basement stays dry and your foundation remains strong. To get started, request a free basement waterproofing inspection and quote today.