A subgrade is the first foundation under a road or pavement. It is usually composed of the area’s native soils or materials, though a subgrade can be made of imported materials if native materials are not sufficient for a good foundation.
Since the subgrade is the foundation for the construction, it needs to be as strong and as uniform as possible to create an optimal foundation for the road or pavement. Explore the steps to prepare subgrade surfaces below.
Steps to Prepare a Subgrade Surface
The first step to preparing a surface to be used as a subgrade is to clear any surface vegetation, stones, and other foreign or extraneous materials, stone formations, and debris in a process called site clearing. Any holes or irregularities in the ground are filled in or otherwise corrected. The topsoil is also removed in a process called “reduction to level” to create a smooth, level surface.
Next, a geotextile is often laid down to create a barrier between the native soil materials and any added materials. Geotextile is a permeable, durable fabric that can separate and reinforce the soils while still offering drainage.
Soils are added on top of the materials to increase elevation and to create a smooth and level surface. Additional soil can be added to create embankments to aid in water runoff. The soils are then compacted by driving over the soil’s surface with a piece of heavy construction machinery called a roller to create a level and smooth surface. The subgrade is then ready for whatever other layers the construction of the road or pavement calls for.
Creating a strong and uniform subgrade lays the foundation for the entire project, so it’s important to do each step correctly for optimal results and a quality finished project.