Page 377 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

ROADWAYS 8.39

In general, shovels do best in banks that are about 15 to 25 feet high. Soft, sliding banks of
sand or gravel provide best digging when they are very high, but there may be danger from slides.
If the cut is considerably deeper than the favorable bank height, it may be taken in two or more
layers or benches. On through cuts with a fairly level cross section, as in Fig. 8.29(A), the top is
removed first. On sidehills there is an option of taking the top first, as in (B), or cutting the toe,
then the top, then the floor of the upper cut, as in (C).
It is first necessary to build a haul road between the start of the shovel cut and the fill. Most of this
may be already provided by highways or construction grading. It should be wide enough for two
trucks, although for short or small jobs, one lane with turnouts may be adequate. Slope up to the
shovel should not be over 15 percent, although in special cases, grades up to 35 percent have been
used.
If no natural turnaround exists at the start of the excavation, and the grade is easy, trucks may
be backed in at first. As excavation progresses, the pit floor will provide turning space.
The roads in (B) and (C) are usually cut by dozers. They allow a rotary movement of one-way
traffic past the shovel on its first cut on each level. They eliminate the necessity of turning at the
shovel in cramped quarters. However, they may be too expensive or inconvenient to build.
When there is no through road, the shovel starts each level by taking as wide a cut as it can
reach, as in Fig. 8.30 (top), to allow space for two-way traffic, turning, and spotting two trucks
at a time. Subsequent cuts are made about half as wide to facilitate loading and truck movement.

FIGURE 8.29 Sequence of shovel cuts. FIGURE 8.30 Through and side cuts.