What Do You Know About Soil Types?

Backfill Soil

Whenever contractors excavate foundation trenches or holes for a building’s footings, they fill them with soil. This is what’s known as fill soil. In most cases, the refill material is the native soil. However, some use dumped, engineered, or hydraulic fills during construction.

Coarse-Grained Soil:  Also known as granular soil, coarse-grained soil is a mixture of gravel, sand, and fine materials with larger grains, typically over 0.075mm. This soil has low plasticity and is compact enough to be used for backfilling. Their engineering characteristics are determined by their relative proportions, density of packing, and the size of soil grains.

Fine-Graded Soil:  Tiny soil particles, lower than 0.075mm in size, are considered fine-graded soil. Sand, clay, and silt are the best examples. Because of their medium plasticity, these soils are sometimes used as backfill material.

Commercial By-Products: Here, we have fly ash and furnace slag, two light materials that are used for backfilling or as additives for sticky clay during construction. Which materials builders will use depends on the property of the backfill by-product.

Native Soil Layers

Any soil that occurs naturally in a particular area is known as native soil. When building, contractors dig out the undisturbed soil and place it back. These soils can be modified by infusing them with sand, porous ceramic soils, or peat. The resulting soil is more stable, hence it is suitable for building the foundation.

Whether or not you’ll use native soil depends on the conditions of the soil, weather, and activities on the site.

Native soils can be any of the following:

Loam Soil: Made up of silt and sand, loam soils are known to hold moisture and drain well. On the flip side, they get eroded fast and don’t provide enough support to the foundation.

Clay Soil: It’s a sticky type of soil that has fine grains. This soil shrinks when it’s dry and expands when it gets wet. Because of this, it’s not good for construction.

Sandy Soil: This is a light and dry type of soil with low nutrients. Unlike clay, sand doesn’t expand or contract. However, it gets washed away over time.

Shale: When clay, quartz, and other minerals compact over time, they form a flaky type of rock that’s known as shale. This soil can expand and contract if it has a lot of clay.

Man-Moved Soils

Any soil that’s moved from one area to another for construction purposes is known as man-moved soil. The soil can be excavated or dredged from a riverbed or sea bottom. These soils help reduce wastage. However, not all have the desired bearing capacity, hence, they have to be compacted after the foundation has been built. Failing to do so could set the stage for foundation settlement, which can damage your building. 

Weak or shifting soils don’t have to sound a death knell to your foundation. If either condition exists, contact Tar Heel Basement Systems to schedule a free inspection. Our foundation experts will check your foundation’s condition and recommend an underpinning solution that will stabilize it. 

Holly Richards-Purpura

Content Writer

Holly is a Content Writer for Groundworks who has written and edited web content for the foundation services industry for almost 10 years. With a background in journalism, her passion for the written word runs deep. Holly lives in Columbus, OH, with her husband. Along with educating homeowners, she also has a big heart for the Big Apple.