Soil Classifications and How They Affect Construction

soil testing brisbane

Soil is classified into many different categories and the type of soil you build on can have ramifications for your structure, many years after it has been built. This article explains the different soil categories, the various environmental conditions that can affect residential and commercial construction and structural foundation requirements for each soil type.

Reactive soils explained

Soils are classified according to their ‘reactive’ qualities. That is, how the soil reacts when subjected to varying moisture conditions. All soils that possess a high clay content will typically see a reduction or expansion in overall size, depending on the amount of water present and are often labeled reactive for this reason. The degree to which the soil’s composition is altered and changed determines its classification.

Some soil types are more prone to size fluctuation than others and it’s important that this is evaluated with a professional soil test, to ensure that your structure’s foundation is engineered to prevent the risk of soil deviation that could ultimately prompt the structure to gradually sink over time (think Leaning Tower of Pisa) or collapse entirely.

Soil classifications

To make certain that the correct style of flooring is used for your residential or commercial structure, your building site must be inspected by a geotechnical engineer, who will extract soil fragments, test them under lab conditions and designate a soil grade based on the test results. This grade will identify the reactivity of the soil and enable the civil engineer responsible for building the structure to determine the style of foundation required.

The following is a list of soil grades with a description of each:

A – Highly stable, doesn’t react. This grade is common to all sand and rock-based locations. The surrounding earth material shows minimal to no movement at all in the presence of altered water content conditions.

S – Minor reactivity. Soil labeled S class may undergo minor movement when the water content is altered.

M/M-D – Moderate reactivity. This grading indicates that a location’s soil may see a reasonable amount of ground shift when the soil’s qualities are modified by water and other environmental factors.

H1/H1-D – High reactivity. This classification indicates a high degree of earth movement when soil conditions change.

H2/H2-D – Very high reactivity. This grading denotes a very high degree of movement when soil conditions change.

E/E-D – Extreme reactivity. Changing soil conditions may result in extreme earth material movement.

P – problematic. For locations that are identified as having P grade soil, it means that the earth material’s ability to steadily support a load is unsatisfactory. Such locations may be categories as P grade for a number of reasons, including erosion issues, soil deterioration, delicate soils and so on. In such locations, the soil may exhibit chronic deformations as a consequence of irregular and uncommon water content conditions. Those wishing to construct on a location that has been determined to have P class soil, must contact a specialist engineer.

Environmental conditions that can impact your foundation

Even with the most appropriate structural foundation for your location’s soil, unforeseen and dramatic changes in environmental conditions can be problematic. The reactive nature of a particular soil type may create stresses in the foundation, resulting in the development of cracks in the structure.

Such environmental conditions that could disturb your foundation include:

Prolonged rain – when extensive water deposits accumulate due to extended periods of rain and do not have sufficient time to adequately dry up and drain away, the water will permeate into the ground and can potentially disrupt and damage the foundation. Effective drainage will help to safeguard against this.

Prolonged drought conditions – when the soil surrounding and beneath your structural foundation is deprived of moisture for an extended length of time, it has a tendency to contract and fall away from the foundation. Ensuring that the soil around your structure is watered occasionally, will help to prevent this from occurring.

Lack of proper balance concerning plant distribution around the property – as discussed above, excess water from prolonged rainy periods can be detrimental and the same principle applies to the irrigation of plants around the house/building. Having a lot of plants that are watered regularly on one side of the property and a complete absence or very little plants on another side, can result in different soil conditions, potentially causing cracks and deformations to develop in the structure.

How soil types impact foundation designs

No matter what classification your soil is deemed to be, it’s just a case of having a foundation designed that caters to the soil and the dimensions of the structure being erected atop of it. Something a civil engineer is able to do. Typically, soil types with only mild or no reactivity such S and A grade will only require a standard foundation design with horizontal beams under the outer edges, while locations with other soil types will need additional reinforcement. This involves the placement of multiple beams throughout the cross-section. This extra support protects the foundation from deformations caused by any shifts in the soil.

For locations that problematic soil types (H, E or P), an engineer needs to be called in to perform a thorough inspection of the premises and provide instructions on how to safely build atop the foundation without the risk of compromising the integrity of the structure. This will typically entail the installation of subterranean pylons beneath the foundation to provide extra support. The pylons must be inserted below where water is known to permeate the ground soil.

For professional bitumen, tar and asphalt services for your next construction project, get in touch with a trade qualified soil testing specialist today.

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