Page 376 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

8.38 THE WORK

FIGURE 8.28 Fixed turn patterns.

big tires and dirt roads. It might take such a machine a half mile of level road to reach top speed
in its top gear, and this distance is longer than the average scraper haul.
A favorable grade will encourage rapid acceleration, but it is likely to make high speed danger-
ous. And for every favorable grade in a round trip there must be an unfavorable one to balance it.
Scrapers are rough-riding vehicles. While the big tires absorb bumps, no way has been found
to fit them with shock absorbers, and bouncing will prohibit full speed unless exceptional atten-
tion is paid to maintaining the haul road.
Scrapers with overhung, two-wheel tractors are likely to develop a rhythmic galloping effect
even on smooth roads, unless equipped with a cushion hitch.
Hauler speed is discussed under Travel Resistance in Chap. 12. When there is no time to work
out level ground performance in detail, figure 40 percent of top speed in the highest gear to be
used for hauls up to 1,500 feet, 50 percent to 2,500 feet, and 60 percent from there on.

SHOVEL CUTS

Through cuts are made by excavators or front shovels and trucks when the original surface can-
not be readily leveled for scraper operation, when the ground is rocky or wet, when the fill is too
soft or too narrow for surface dumping, and when the haul is too long for scrapers.