Page 538 - Moving the Earth_ The Workbook of Excavation

PIT OPERATION

10.44 THE WORK

FIGURE 10.28 Selective digging.

Mixing is also done directly at the bank by digging from one formation, dumping on another,
and then loading the two together.
If the layers are horizontal, digging in slices from the bottom up will mix them. Scrapers may
bring to the top of the bank material to be mixed into it by loading.
Pockets. When an irregular deposit, with sloped or vertical edges and numerous interruptions, is
dug from the bottom, a cluttered pit is left. All parts of it are accessible to digging equipment and
trucks, but there may be little room to maneuver and none for storage. If the digging is done from
the top, the area may become a badland, with little or no access and probably deficient drainage.
Such areas should be dug out, or smoothed down, at the first opportunity, particularly if any
further work is to be done behind or under them. Many pits have strangled themselves out of busi-
ness while they had ample reserves, because leaving obstacles to orderly digging has forced hap-
hazard development with increasing excavation and hauling costs.
Cutting a pit floor by pursuing a good vein across it is a bad practice that is sometimes difficult
to avoid. In general, it should not be done unless its value is sufficient to cover the cost of back-
filling. If floor and walls of the cut are smoothed off, it may be filled with material to be stored
which can be recovered when the whole floor is lowered. If no further digging is to be done in the
floor, the slot can be filled with waste of a type which will not become too soft to carry pit traffic.
Cuts down from a floor, whether pockets or the start of new levels, should be near the outer
edges of the pit.
Boulders. A common problem in pits which are dug without blasting is the occurrence of boul-
ders too large for the loading or processing machinery. These are found in glacial and stream
deposits, in disintegrated rock, and near steep slopes.