Page 497 - Moving the Earth_ The Workbook of Excavation

PIT OPERATION

PIT OPERATION 10.3

FIGURE 10.1 Steps in strip-mining a lens.

If the spoil piles are smoothed over where they fall, without substantial removing, the original
grade will be raised in a ridge parallel with the beginning of the work, and lowered at the last cut,
these changes corresponding to the land and the dead furrow of the ploughed field.
Bulldozers. Where the deposit is shallow and the pit narrow, bulldozers make good stripping
tools, particularly when the land slopes across the pit. Figure 10.3 shows a sequence of operations.
This can be repeated in successive strips across the deposit if conditions remain the same.
Such shallow overburdens seldom require blasting, but use of a rooter may speed the digging.
It will be noted that this machine backfills the face of the pay layer so that work must be done
from the surface of the seam.
Bulldozers are also essential auxiliary tools in the heavier stripping work.
Scraper. Scrapers, or pans, are used in sidecasting, haul-away, and combined stripping. Their
best application is to soils that can be dug easily with the power that is available, or that can be
broken into fine fragments by ripping or blasting; and that are not deep enough to justify the use
of shovels with enough reach to give the pit the width it requires.
Figure 10.4 illustrates a method of scraper use. These are considered sidecasting since the spoil
pile is placed immediately behind the pit, but otherwise the work is identical with haul-away with
the same machines. A particular problem that becomes more important as depth increases, is
maintenance of haul roads across the pit and up the spoil bank.