When a surface appears like that in the photograph to the right, the contractor fails to earn the incentive for smoothness and this project is negatively received by the public using the corrugated surface. This is avoided by paying attention to rolling speed, especially with vibratory compactors.
Highway-class vibratory compactors need to make 10 to 14 impacts per foot (33 to 46 impacts per meter) with each drum. Larger diameter drums can produce acceptable results with wider impact spacing; smaller diameter drums need closer impact spacing to achieve smoothness.
Ingersoll Rand recommends the following:
- Drums under 40 inches (1015 millimeters) in diameter: 14 impacts per foot (46 impacts per meter)
- Drums up to 50 inches (1270 millimeters) in diameter: 12 impacts per foot (39 impacts per meter)
- Drums up to 59 inches (1499 millimeters) in diameter: 10 impacts per foot (33 impacts per meter)
The largest compactors, with drums larger than those listed above, may produce acceptable surface smoothness results with drum impact spacing as low as 8 impacts per foot (26 impacts per meter). For assurance of performance, it is always recommended to set up a test strip to prove the rolling pattern and rolling speed. Appropriate density and smoothness tests will confirm the rolling pattern and speed selected will give the desired results on the test strip.