What usually causes settling in soils?

Settling in soils is primarily caused by the consolidation of supporting soil. Consolidation refers to the process by which soil particles rearrange themselves and reduce their voids due to the expulsion of pore water over time when subjected to load. This is particularly significant in saturated soils, where excess pore water pressure diminishes under changing loads. As the load is applied, the soil's structure undergoes a gradual decrease in volume, leading to noticeable settlement on the surface.

Consolidation is a phenomenon that can occur in various soil types, particularly clays, which exhibit high compressibility. It can be driven by construction activities, the addition of structures, or changes in applied loads on the soil.

Temperature changes may influence some physical properties of soil, but they do not directly cause settling. Similarly, while variations in groundwater levels can affect pore pressure and temporarily induce some ground movement, they are not the primary factors responsible for the ongoing process of settlement. The flow of water through soil is important for water drainage and can affect pore pressure, but it is not a direct cause of settling. Therefore, the consolidation of supporting soil stands out as the primary mechanism behind settling in soils.