The type of soil that your property is built on is a crucial factor that determines the stability, longevity and overall safety of a structure’s foundations. Therefore, different soil types will have unique properties that will affect their ability to support a building’s load, react to moisture and withstand changes in their surrounding environment. Understanding the types of soil on your plot and their properties is key to designing a foundation that stands the test of time.
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Clay Soils
Clay soil is a problematic soil type for foundations. Typically composed of very fine particles, clay soil is notorious for expanding when wet and shrinking back when dry. This constant movement is known as ‘heave and subsidence’, both of which can put stress on a foundation.
During wet periods, the expanding clay will exert upwards pressure, and dry spells will cause the ground to pull away, leaving parts of the foundation unsupported.
Both of these can lead to significant structural damage, including cracks in walls, floors and the foundation itself.
To build on clay, the foundations of a property must be deeper and extend past the reactive top layer of soil. Pile foundations can transfer the load to more stable ground beneath the clay, and reinforced strip foundations can also be used to mitigate the risk. Where clay soil is present, proper drainage systems are also crucial in managing moisture levels effectively around the foundation.
Sandy Soils
Sandy soils are typically found in coastal regions and some inland areas of the UK. These soils are more granular in nature and highly permeable, allowing water to drain quickly. They have a good load-bearing capacity; however, their loose structure can pose challenges, especially in areas prone to erosion.
When working with sandy soil, foundations typically need wider and deeper footings to distribute the load more evenly. Soil compaction and stabilisation techniques can also help to increase the soil’s density and load-bearing capacity.
Loam Soils
Loam is a mixture of sand, silt, and clay. This is often considered the ideal soil for construction due to its balanced properties. It will drain well, won’t expand or shrink as dramatically as clay, and has good load-bearing capacity. These characteristics make it stable and a predictable base for a foundation. Loam soils are usually found in agricultural regions of the UK and are typically stable and easy to work with.
However, whilst loam soil is a great base, there are some considerations to keep in mind when working with it. A geotechnical survey is still recommended to ensure the soil composition is consistent and to remove any organic matter or tree roots that could decompose and cause shifting over time.
Chalk Soils
Chalk soils are often sound in regions such as the South Downs, Chiltern Hills and parts of East Anglia. These soils are typically stable and have good load-bearing properties; however, they are highly porous and can absorb large amounts of water. This can lead to problems such as sinkholes and subsidence if not properly managed.
When dealing with chalk soils, strip foundations with adequate drainage systems are recommended to prevent water accumulation. In areas where chalk is softer or prone to dissolution, deeper foundations or reinforced concrete rafts can be necessary for increased stability.
Peat Soils
Peat soils are common in the Somerset Levels, East Anglia and parts of Scotland. Peat is comprised of decomposed organic matter and is typically found in wetlands and bogs, making it highly compressible and waterlogged.
Building on peat is extremely different and often recommended against. As the organic materials in the peat decompose and the soil dries out, the ground can compress and shrink away significantly, leading to foundation failure.
Where building on peat is unavoidable, specialist foundations will be necessary. This will involve excavating the peat layer entirely and then replacing it with a suitable fill, or using deep pile foundations that extend through the peat to reach a more stable layer of soil below.
Rock Soils
Rocky soil is a stable and reliable base for a foundation, has an extremely high load-bearing capacity and is not affected by changes in moisture content. Building on rock minimises the risk of shifting, settling or erosion.
However, where rock is an ideal foundation, the main challenges lie in the excavation and levelling process of the build. Solid rock can be difficult to create a flat surface for the foundation. Yet in some cases, a foundation may be laid directly onto a properly prepared rock surface.
How To Deal With Soil Variability
Across the UK, soil conditions can vary significantly. Therefore, it’s not uncommon to find different soil types across a plot, complicating foundation design.
This is why working with a professional in groundworks and foundations is important, and carrying out a geotechnical survey is vital to identify the specific soil types on site, and their distribution. Using this information, engineers can design foundations that accommodate the soil conditions and ensure building stability.
What’s more, by working with a specialist in groundworks, you can ensure that the right drainage systems are installed and that soil stabilisation is included in your plans where needed.
What Affects Can Soil Type Have On Foundations?
When building a property, whether it’s commercial or residential, a strong foundation will keep it stable and ensure longevity. Ensuring that you have the right foundation, depending on the soil found on your building site, is important, as soil types can affect your foundations in many ways.
Load-Bearing
A key reason to identify the soil you’re building on is its ability to support weight. A building will be heavy; therefore, your soil may need additional support from foundations to hold the building. Some soils have high load-bearing capacity, making them great for foundations, whereas other soils are only moderately supportive, meaning they can shift under heavy loads.
Moisture and Damage
Poor drainage can cause water to pool, weakening foundations, leading to instability. To prevent water pooling, considering how the soil type manages moisture is key. Clay soils often expand when wet and shrink when dry, causing movement in the foundations, whereas loamy soils provide good drainage and stability.
Erosion and Stability
Another key consideration when completing a building project is the external factors that may affect the build. Erosion-prone soils can easily shift and fall over time, compromising the stability of the structure above. To prevent soil erosion, retaining walls or gravel layers may be needed.
Expansive and Reactive Soils
Specific soils can react to local conditions, such as changes in moisture. Clay soils are highly expansive and can cause the foundations to rise or settle unevenly. This movement can have a noticeable impact on the property, causing cracks in walls or sloped floors. Clay soils will need special considerations before building work commences.
If you’re looking to create a strong and stable foundation for your next building project, get in touch with Wilsons Groundworks. Our experts in groundworks in Bristol have the knowledge and experience to support your project. Give us a call on 01761 231802 to find out more about our services.