Concrete slabs on grade require which type of soil base for support?

Concrete slabs on grade are designed to be supported by a soil base that provides stability and strength. A level, stable, and dense soil is essential because it can efficiently distribute the load from the concrete slab over a wide area. Such a soil base helps to prevent uneven settling, cracking, or structural failures of the slab due to shifting or movement of the ground beneath.

Stable soil minimizes the risk of displacement, compression, and other issues that can arise from less stable conditions. Dense soils, such as those that have been well-compacted, generally provide better load-bearing capacity compared to loose or organic soils, which can settle over time and may not provide the necessary support for a concrete structure.

In contrast, loose, organic soils can compress and change in volume with moisture fluctuations, leading to instability. Highly compressible or expansive soils can swell when wet and shrink when dry, causing significant movement and stress in the slab. Sandy soils with low compaction may also fail to provide adequate support and stability, particularly under load, which can lead to uneven settling.

Therefore, a level, stable, and dense soil base is critical for ensuring the structural integrity and longevity of concrete slabs on grade.