Page 504 - Moving the Earth_ The Workbook of Excavation

PIT OPERATION

10.10 THE WORK

FIGURE 10.10 Overburden removed with dragline and shovel.

Very large draglines may be able to dig solid shale, but not sandstone. In such formations only
the sandstone layers would need to be drilled and blasted.

Grading Spoil. The spoil banks from light stripping operations can be leveled by bulldozers,
scrapers, or graders. However, the huge machines used in heavy stripping leave such large, coarse
piles that the biggest dozers cannot reduce them economically.
The problem is largely a new one, as prior to legislation of the subject, most of the stripped
areas were left as permanent wastelands.
If a front shovel is moved short distances frequently, the high peaks of its spoil ridge are greatly
reduced, as indicated between Fig. 10.11(A) and (B). The more even ridge top is the more readily
broken down by a bulldozer working along its crest.
If the boom and stick are longer than required by the height and slope of the bank, the ridge
and trough surface can be eliminated by building out level with the old bank, (D) and (E), instead
of heaping toward the pit, as in (C). Accurate grading cannot be expected in such overhead dump-
ing, but the bulk of the irregularities can be eliminated.
A dragline with extra boom length can build a flat-top pile by dumping against the bank near
the top at full reach, and building out the edge by shorter or longer swings as required.
Approximately the same result can be obtained with a slightly shorter boom by throwing some
spoil.
Another dragline procedure, requiring extra clearance at the pile foot, is to drag the top of the
completed pile onto the slope to the pit, as in (F) and (G).