What must be done to compressible soils before constructing foundations?

To properly prepare compressible soils before constructing foundations, it is essential to remove them. Compressible soils, such as clay or silt, can lead to significant settlement issues if left untreated, as these types of soils tend to shift or compress under load over time. Removing these soils allows for the installation of a more stable foundation, typically replacing them with more suitable materials that provide a solid base capable of supporting the weight of the structure. This process mitigates the risk of foundation movement and ensures greater longevity and stability for the building.

While options like compacting or stabilizing might seem like viable solutions, they do not fundamentally address the problems associated with compressible soils to the same degree as removal, which is why those approaches would not be the best practices in such circumstances.