Page 271 - Moving the Earth_ The Workbook of Excavation

PONDS AND EARTH DAMS

PONDS AND EARTH DAMS 6.7

The windrow is usually moved by standing behind it and digging with a short dump cable, so
that the loaded bucket can be picked up without pulling in. It is swung to dump as far back as pos-
sible, and a level runway made to permit the dragline to work along the rim of the original cut, as
in Fig. 6.5.
If the pile is too large to allow the bucket to reach across it, part of it may be dug away, as in Fig.
6.6, and the balance removed at the same time that fresh ground is dug.
The runway is normally made at the original grade, as vegetation or drying makes it firmer than
the soil underneath. However, if the soil is hard to cut, the runway may be lowered to improve digging
efficiency. If digging is easy, and the dug soil dry and firm enough to support the shovel, the ramp
may be made higher, as in Fig. 6.7, to increase the dumping height. The cross section of a pile increases
about in proportion to the square of the height, so the advantage gained is important. The freshly
moved dirt is left higher than the undisturbed part of the pile, as it may settle seriously under the
dragline. If possible, the machine should be kept on the consolidated part.
If the pile has a wide top, it may simply be leveled by a bulldozer, or by the dragline raking
and patting it as it travels along it. However, it should be remembered that the tops of piles are
treacherous at best, the machine should be kept back from the edges, and the pile watched carefully
for evidence of caving, particularly toward the digging.
As shown in Fig. 6.7, a dragline working on top of a pile is able to not only move the whole pile
back but to dig the ground under it in one operation.
For even wider ponds, additional cuts may be made. Each additional slice involves moving all
the material which has been dug, with increasingly complicated patterns, and expense mounts
rapidly. Usually more than two cuts are made in one direction only when the operation involves
cleaning off vegetation and shallow digging. In deep work, trucking the spoil or removing it with
conveyors is more economical when several rehandlings with a dragline are necessary.

FIGURE 6.5 Double handling.