surface of an existing road that is to be replaced is also
known as the existing grade. The subgrade of a road
is a prepared base for the placement of base-course
materials. The base course is a select layer of
well-compacted soil that is placed in compacted lifts
on top of the subgrade. This compaction can be
accomplished by mechanical stabilization or chemical
stabilization. The surface course and the shoulders
complete the road. The surface course is usually
concrete or asphalt and is part of the road that vehicles
travel on. The shoulder of the road performs as a
retainer on each side of the surface course and
provides an emergency parking area.
The crown of the road is an established slope from
the center line of a roadbed to the outside of the
shoulders and allows for excess water to drain from
the surface into either a V type or flat bottom type of
ditch. The area that covers the entire width of the road
Table 15-1.—Volume Changes
15-11
