U&M Group

Which Soil Is Best Suited to a Pile Foundation?

Thursday, April 25th, 2019 AT 12:30PM

Pile foundations are most commonly associated with strengthening a building’s existing foundations through underpinning, but this isn’t its only use. Piling is also sometimes the most suitable technique for new-build foundations. The crucial factor is frequently the type of soil below the structure.

Soil Quality and Pile Foundations

The reason soil quality often determines the need for pile foundations is that weak soil or soil that’s saturated with water may be unable to support traditional foundations. The soil is likely to give way, resulting in the foundations — and therefore the structure they’re supporting — sinking further down.

If these conditions persist to a depth of over 2m, piling can be the answer. This solves the problem by taking the weight down through the weak soil to a firmer layer of soil or rock below, allowing the weight to be distributed down to a secure basis that can support the building.

Which Soils Are Weak?

The types of soil that most often require piling are those with high clay or silt content since these are fine-grained soils. They tend to collapse more easily, or else cause more uplift when they freeze.

Sandy soils are stronger but can still cause problems, while soils with high organic content can also be too weak to support traditional foundations. This is most likely to be on land previously used for agriculture or horticulture, but it can be found elsewhere.

Clay and silt are especially vulnerable if they’re saturated since they liquefy easily. However, anywhere that has a high water table or shows signs of being marshy are potentially vulnerable, and piling should be considered.

New-Build Foundations and Underpinning

If you’re planning a new build, it’s vital to commission a thorough survey of the soil quality before deciding on how to proceed. If the survey shows the soil as very weak, it may be necessary to abandon the project altogether, but piling can be used to take advantage of stronger levels deeper below the surface.

On the other hand, an older property that’s suffered from subsidence can benefit from being underpinned by piling. The soil may not have been properly surveyed at the time of building, or conditions may have changed — a rise in the water table, for example. Quite apart from often being a more cost-effective technique than traditional underpinning, piling becomes a must if the soil is weak.

If you want to know more about which soil is best suited to a pile foundation, feel free to get in touch with us.