Understanding Soil Types in Construction

11th September 2019

Understanding Soil Types in Construction

Understanding soil types is extremely important in the construction industry, particularly if you are utilising heavy machinery such as all-terrain cranes or digging trenches. How the ground cover and subsurface levels interact and change over time, especially in the presence of water, is critical knowledge for avoiding incidents. You should always invest in a site-specific survey performed by a geotechnical engineer before starting work, but having a general understanding of how the ground works is helpful for everyone on site. In this article, we will give a brief introduction to the soil types most commonly encountered on building sites.

Boulders, Gravel and Rocky Ground

Rocky ground is one of the most stable to work on. Larger rocks are called boulders, and in order of decreasing size rocky ground can also be described as coarse, medium and fine gravel. These descriptions typically apply to soil that is less than 5% clay or silt. Rocky ground usually drains quickly and is ideal for driving heavy machinery and mobile cranes on as it is typically resistant to compaction.

Clay Soils

Clay soils are commonly smooth to the touch, mouldable by hand and compactable. They tend to crack when dry and can sometimes be very stiff. Clay soils are less than ideal for utilising mobile all terrain cranes as they move over time, particularly when they’re wet. Crane outriggers need to be checked regularly to make sure they are still in solid contact with the ground to avoid the possibility of the crane overturning.

Sandy Soil

The defining characteristics of sandy soils is small particles that are visible to the human eye, and virtually no particle cohesion when dry. Much like clay soil, sandy soil can pose issues for cranes in wet and dry weather as the small particles are able to move and sink over time meaning outriggers should be checked regularly.

Organic Soil

Organic soil contains organic matter and silt. Sometimes, the organic matter is discernibly plant material such as grass and decomposing roots, and at other times, it is amorphous dark brown or black soil. Organic soil ranges in compressibility from dense compact soils to very loose loamy soil that is valued by gardeners, but shunned by construction workers because it can often cause machines to get bogged, particularly in the wet.

Composite Soils

In practice, most soils are a combination of one or more of the above types, particularly if the worksite exists at different depths due to excavation work. This is another reason to have a site inspection performed by a geoengineering professional.

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