Is it necessary to remove the soil before installation?

Removing the topsoil before installing piles is more than just a formality; it's a crucial step that impacts the longevity of the foundation.

Is it necessary to remove the topsoil for a pile foundation?

One of the most common questions that arises when preparing a site for construction is whether it's necessary to remove the topsoil for a pile foundation. This step is often controversial: some consider it unnecessary, especially when installing screw or bored piles, while others insist it's essential for the longevity of the entire structure. In this article, we'll explore when it's absolutely necessary to remove the topsoil and how this affects stability and service life.

What is a topsoil and how does it differ from a building foundation?

A topsoil is the uppermost layer of soil, rich in organic matter, microorganisms, and a loose structure. It is suitable for agriculture, but completely unsuitable as a load-bearing foundation for any permanent structure. This soil is susceptible to subsidence, erosion, decay, and seasonal movement, which creates the potential for foundation distortion or even structural deformation.

Why is a topsoil required to be removed even when installing piles?

Even though a pile foundation rests on denser soil layers, penetrating the upper horizons, leaving a topsoil can lead to a number of problems. For example:

·         Uneven ground conditions can cause the foundation or slab to warp;

·         Decaying soil can cause depressions between piles, which can spoil the appearance and disrupt the geometry of the structure;

·         Moisture accumulation can accelerate corrosion of metal components and the deterioration of concrete piles;

·         Difficulty installing supports level arises;

·         The cost of subsequent finishing work increases due to the need to level the surface after installation.

Therefore, if you want to purchase a turnkey pile foundation with a guarantee of durability and stability, it is important to mechanically remove the topsoil down to firm soil. In some cases, removing 15–20 cm is sufficient, while in others, up to 40 cm is sufficient, especially if the site is marshy or previously used for gardening.

When topsoil removal is necessary

In some cases, removing the topsoil is not necessary, but only with proper preparation:

·         If the pile foundation is being installed under a temporary or lightweight structure, such as a utility room or outbuilding;

·         When deep screw pile drive technology is used, bypassing soft horizons;

·         If reinforced reinforcement and rigid strapping are provided around the perimeter;

·         When constructing temporary platforms not designed for heavy loads.

However, even in these cases, we recommend at least partially removing loose soil and replacing it with a compacted bed of crushed stone or sand to minimize the risk of subsidence and deformation.