What is the cause of settlement?

Settlement refers to the gradual downward movement of the ground surface, often as a result of the loading of the soil by structures such as buildings, roads, or other infrastructure. When a significant weight is placed on the soil, it causes the soil to compress and rearrange, leading to a reduction in volume and creating a downward movement of the ground. This process can be influenced by the type of soil, moisture content, and the amount of weight applied.

The other options relate to various soil and environmental conditions, but they do not accurately describe the primary process involved in settlement. While soil expansion due to rainfall or soil compaction from earthquakes can affect soil stability or condition, they do not represent the mechanism by which settlement occurs due to structural loading. Natural vegetation growth, although it can influence soil stability and erosion, is not a direct cause of settlement in the context of structural load.