Page 364 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

8.26 THE WORK

SCRAPERS

Scrapers, which are described in Chap. 17, are the standard excavator for alternating cuts and fills,
where the soil is soft or fine enough for them to work, or can be made so by rippers and explo-
sives, and where the haul is too long for dozers.
Preparation. The first requirement is to smooth over the cut and the fill areas so that scrapers
can work them. This is usually a dozer job. The ground is cleared of vegetation and boulders,
holes and gullies are broken in and ramped over, sharp ridges beveled off, side slopes notched,
and turning places graded off.
It is not absolutely necessary to prepare the whole area in order to have the scrapers move in.
Their work can start on the high part of the cut and the low part of the fill, while the dozers are
clearing and smoothing the balance of the area.
If the cut has a high side, it is cut to a passable driveway by straight pushing or sidecasting.
The bottom of this cut is sloped oppositely to the hill.
If the hill is high in the center of the cut, the hump is graded off sufficiently to afford good
footing for scrapers.
It is sometimes economical to make small fills in areas which are to be lowered, and small cuts
under future fills in order to smooth out working areas quickly.
When a dozer is not available, a scraper can smooth moderately rough ground by driving
through it with the knife held low enough to cut off the bumps and high spots. If the tailgate is
held near dumped position, it will act as a dozer blade.
Scraper work on side slopes is simplified by first cutting a shelf with a dozer. If no dozer is
available, the scraper can be taken uphill to the start of the cut, the blade dropped, and the scraper
turned to dig along the upper cut line. The turn will cause the edge to cut most deeply on the uphill
side, and if done repeatedly, will level the digging area, or slope it oppositely from the hill.

Cutting Ridgetops. If the slope up from the fill is too steep for the scraper to climb, it may be
broken down into a ramp by dozers, or the cut made with an excavator.
If the slope away from the fill is too steep for scrapers, the top can be lowered by the combined
work of scrapers and dozers, as shown in Fig. 8.18. Full-trailer scrapers will dig across the cut as
they turn, as in (A). Semitrailers can be backed up to the edge, as in (C), and if a snatch tractor is
available, can be backed over it. Digging is then done straight toward the fill.
The undug lip left by the first method is pushed over the edge by a dozer, as in (B). This fill-
ing, and the cutting into the slope, will extend the floor and allow scrapers to work farther back.
Eventually the bank will be lowered sufficiently to make it practical to break it down with doz-
ers (D), so that scrapers can go through to dump on the far side, or turn to continue hauling in the
original direction.

Shaping. The outer edges of the slope should be determined before starting work so that steep
banks may be cut to final grade from the first. They are taken down in a series of steps. If the slope
is 1 on 3, and the scrapers are taking 6-inch slices, each new level cut should be 18 inches farther
from the bank than the previous one, as shown in Fig. 8.19.
The slope should be checked frequently by engineers for correctness, and trimmed off by a
grader working on the floor of the cut, as it may become very difficult to reshape when the floor
has been cut too far down.
The floor of the cut should slope down toward the edges. This slope may be originally estab-
lished by an angle dozer or a grader, after which it will tend to perpetuate itself, as the weight of
the machine will be greater on the down side so that it will tend to cut low there. If the slope
becomes too great, the upper part may be readily planed off.
Machinery may not be available to shape the original surface, or the crown may be lost because
of oppositely sloping strata or by careless operation. A scraper can cut a crown by taking advan-
tage of the fact that the oscillating tractor part does not affect the side-to-side tilt of the knife,
which is determined almost entirely by the rear axle. A gouge taken heading up a slope can be