Page 382 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

8.44 THE WORK

FIGURE 8.32 Scraper spreading fill.

Thick spreading is liable to flow out of the bowl more smoothly, can be done at higher speed,
and reduces the dump time. However, it tends to make a rough fill which will require slower travel
speeds, or smoothing work with a dozer or grader.

Edges. If a fill is high, the edges may be troublesome and dangerous unless carefully made. The
problems are to keep it at the correct toe alignment, proper slope, at full density or compaction,
and not rolling any machinery off it. These problems are affected by the nature of the fill and by
its height and slope.
Loose fills of sand, clean gravel, or too-dry dirt tend to cave under the weight of machinery
close to the edges. Finer-grained fills may have excellent bearing power if well compacted and
not too wet. However, while being compacted, they tend to squeeze outward, and an allowance for
this creeping must be made when placing the first fill, so that it will not move out past the toe stakes.
The behavior of the fill on edges may be anticipated by making soil analysis or by consulting
with contractors or machinery operators who have worked with the same formation.
Except for allowance made for creeping under load, or spillage from above, which seldom should
be more than a foot or two, the fill is started at the toe line and built up of layers, usually not over
6 or 8 inches, loose. Each layer should be rolled with a tamping roller that is allowed to project
slightly beyond the edge. For this purpose, two or more rollers should be fastened in a single yoke
so that their width will be substantially greater than that of the tow tractor, which should not have
to walk on the edge. This is particularly important with high banks and wheel tractors.
If watering is required for proper compaction, application may be somewhat heavier at the
edge to allow for side evaporation. However, it should not be sufficient to make it soft or muddy.
The fill should slope up at the edges in order to incline the center of gravity of the machinery
toward the center and minimize the danger of caving. If the fill is narrow, it will have a trough
shape, and if wide, it will be flat with raised sides.
This slope is most easily started by a grader or an angle dozer working over the first layer or
two left by the scrapers. Once made, it will tend to preserve itself as the tilt will tend to make the