GRADING AND EXCAVATING

Grading and excavating are cutting the high spots to grade and filling in the low spots. In cutting down the high spots, enough suitable fill material may be removed to fill in low spots. However, it may be necessary to develop other sources of fill material. If the site is on hard and rocky terrain, loosen and break the soil with a dozer ripper. Before fill material can be placed in low spots, a suitable foundation must be prepared. Material of a low-bearing capacity may have to be dug up before the fill is placed.

Base Course

^{The base} course distributes wheel load stresses from the surface pavement to the subgrade. Since stresses in the base course are more concentrated than in the subgrade, the base course must be stronger.

Placement and Compaction

When placing and spreading base course materials on a prepared subgrade, start at the point nearest the source or at the point farthest from the source. Then place the material progressively away from or toward the source, respectively. The advantage of working from the point nearest the source is that hauling equipment can be routed over the spread material, which helps compact the base course and avoids cutting up the subgrade. An advantage of working from the point farthest from the source is that the hauling equipment further compacts the subgrade, reveals any weak spots in the subgrade, and interferes less with the movement of spreading and compaction equipment.

Base course compaction must produce a uniformly dense layer, conforming in every way to specification requirements. The thickness of the lifts should NOT exceed that which can be compacted to the required density. The thickness of the lifts is determined by the size of the compaction equipment, such as 6 inches for rollers and 3 inches or less when using tampers.

NOTE: Optimum moisture content must be maintained during compaction.