Page 368 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

8.30 THE WORK

FIGURE 8.22 Scraper and pusher.

There are also small push plates that mount on the C-frame of a dozer or angle dozer. This
installation is more expensive than the fixed plate, but permits accurate lining up with scrapers,
can be used for pushing big boulders, and can be easily replaced with a dozer blade.
Either type of plate is much less likely to damage scraper rear tires than a dozer blade is.

Loading Effect. Soil and slope conditions being equal, loading time and the size of load in a
particular scraper are determined by the power applied to it, regardless of whether that power
comes from one, two, or three tractors.
The rule of thumb is that 1 pound of push puts 1 pound of dirt per minute in the scraper. This
“push” includes the scraper’s own effort.
Tandem Pushers. It follows that size of scraper loads and speed of loading can both be
increased by increasing pusher power. Additional power may be obtained by using bigger trac-
tors, using two or more tractors together, or in both ways.
The standard arrangement for pushing with two or more tractors is to line them up behind the
scraper. The front dozer pushes the scraper, it is pushed by the machine behind, and sometimes
that is pushed by still another. However, two pushers are much more usual than three.
These tractors must have push brackets at the rear, fastened to the side frames so as to put the
thrust directly against the dozer arms.
Tandem pushing involves extra delays in getting the machines in contact with each other and
loading, but it usually more than makes up for this in extra speed and depth of slice in the cut.
Snatch Tractors. A few contractors use a pull tractor instead of or in addition to pusher tractor(s)
for loading scrapers. Coupling may be by means of a short tow cable, or preferably by a coupling
that locks automatically on contact and can be opened by the puller operator from her or his seat.
The tow cable requires a full stop and the services of a ground worker; the automatic coupler,
a high degree of operating skill.