Page 356 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

8.18 THE WORK

particularly in light soils and shallow cuts. The advanced position of the blade may make it diffi-
cult to turn with heavy loads.
Work is started near the upper slope stakes, at a spot naturally or artificially level enough to
permit the dozer to work parallel with the road centerline, at the upper edge of the cut. A blade full
of earth is dug along the upper cut line, then the blade is lifted and the machine turned downhill
at the same time. After dumping, the dozer is backed until parallel to and touching the upper line.
Another scoop is dug and swung downhill.
One or several layers may have to be dug in one spot to obtain enough fill to build out the shelf
wide enough to carry the dozer. The steeper the slope, the more passes are needed.
The blade is raised sufficiently during the dump to keep the fill higher than the cut so that the notch
will slope oppositely to the hill. This keeps the dozer tilted for efficient cutting, allows for compaction
of the fill when it is walked on, and also provides the proper cross section for a pioneer road.
When the shelf is wide enough to hold the dozer, further procedures are varied to suit the slope,
the soil, the machine, and the operator’s preference. The cut can be lengthened to the end of the slope,
then cut in successive layers to grade and width, or it may be developed to full size in a single cut.
Layer cutting involves more rehandling of the dirt, as the loads dropped from the first cut are
moved again as it is deepened. However, it is easier for a dozer to make shallow cuts, and the angle
blade sidecasts most effectively and puts minimum strain on the tractor when the cut is light.
Deep single cuts make it difficult to trim the bank and may have to be avoided for that reason.
Rock Slopes. If the slope is composed of material that the dozer cannot dig, or that it can dig
only with difficulty great enough to reduce production and increase repair costs substantially, the
material should be softened ahead of the dozer.
Hard clay and soft rock on moderate slopes may be loosened with a tractor-mounted ripper. But if
the rock is hard or the slope is steep, drilling and blasting will probably be necessary for the pioneer cut.
Engineering geologists say slope failures are increasingly common, particularly where heavy
blasting takes place during construction, where natural fractures undermine rock face stability, or
where the slope has long been exposed to weathering.
Very steep or broken slopes call for hand drills. Holes may be drilled along the top line of the
cut or horizontally at the first-floor level. It usually pays to drill closely and load heavily, as ribs
or poorly fractured rock will delay the dozer operation out of proportion to any saving in costs.
When the rock is patchily covered with loose overburden, it may be necessary to dig holes
before drilling. At other times only the exposed rock is drilled, and secondary work done on the
parts that are uncovered during dozer work.
If there is a considerable amount of pioneering in rock slopes, best results may be obtained by
use of light self-propelled drills on crawler mountings. They can reach and work in very difficult
places, and can tow their own compressors except under extreme conditions.
After blasting, dozer sidecasting proceeds in the same manner as in naturally loose soil.
Once the pioneer bench has been established, the character of the rock will determine whether
rippers or drills and explosives should be used to loosen it.
Lower levels may utilize dozer sidecasting, backhoe sidecasting, scraper hauling, or shovel
and truck hauling, depending on the job plan. If the material is used elsewhere, it is of course
desirable to take it away immediately, rather than sidecast it first and then redig and haul it.

Belt Loaders. Once a cut of sufficient width has been made between two areas that are wide and
level enough for turning, a belt loader (see Chap. 14) is sometimes used for widening and deep-
ening the cut by sidecasting if the soil is suitable. This machine may work in only one direction.
It may be followed on each trip by a dozer grading off the spoil.
Excavator. The front shovel or backhoe can be used instead of a dozer for notching a slope. It
can usually do the rough work in one trip, as in Fig. 8.13, but if the bank must be trimmed or the
cut is very deep, it may be done in layers.
When the width of the cut will allow it, it is good practice to keep the shovel on its floor rather
than with one track on the fill. For narrow roads and deep cuts, a small backhoe with a short rear
overhang is desirable. The cut should be kept sloped into the bank to keep the weight off the edge.