What is a subgrade in earthwork terminology?

In earthwork terminology, the subgrade refers to the layer of soil that has been prepared and compacted to provide a stable foundation for structural layers such as pavements, foundations, or other constructions. This layer is critical because it affects the load-bearing capacity and overall stability of the structure built on top of it. Proper preparation of the subgrade ensures that there is minimal settlement or deformation over time, which can lead to structural issues.

The preparation of the subgrade involves grading, compaction, and sometimes the treatment of the soil to enhance its properties. This meticulous process sets the stage for the subsequent layers, ensuring proper drainage and support. Properly executed, the subgrade helps to alleviate the potential for future problems related to settling or shifting.

In contrast, other options refer to different aspects of earthwork. The top layer of soil that is removed is not the same as the subgrade, as it typically refers to the surface layer that might be stripped away for construction. A type of soil testing procedure is important for assessing the characteristics of the soil but does not define the subgrade itself. While vegetation growth is essential in many contexts, the area designated for that purpose is unrelated to the structural considerations of the subgrade.