surface of an existing road that is to be replaced is alsoknown as the existing grade. The subgrade of a roadis a prepared base for the placement of base-coursematerials. The base course is a select layer ofwell-compacted soil that is placed in compacted liftson top of the subgrade. This compaction can beaccomplished by mechanical stabilization or chemicalstabilization. The surface course and the shoulderscomplete the road. The surface course is usuallyconcrete or asphalt and is part of the road that vehiclestravel on. The shoulder of the road performs as aretainer on each side of the surface course andprovides an emergency parking area.The crown of the road is an established slope fromthe center line of a roadbed to the outside of theshoulders and allows for excess water to drain fromthe surface into either a V type or flat bottom type ofditch. The area that covers the entire width of the roadTable 15-1.—Volume Changes15-11
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