Page 128 - Moving the Earth_ The Workbook of Excavation

ROCK, SOIL, AND MUD

3.22 THE WORK

FIGURE 3.14 Plank road.

the variable load, and the twisting reaction to the swing all cause the machine to settle, particu-
larly at the end where the loads are picked up.

PLATFORMS

Platforms, also known as pontoons or mats, are wood supports for machinery working on soft
ground. They are most often used under draglines or other revolving shovels.
Their primary function is to spread the weight of the machine over a wide area. They also pro-
vide a relatively clean, dry place from which to work, and will act as temporary bridges over
ditches and holes.
Construction is not standardized. They are generally made by the contractor who uses them
according to local methods.
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1
In general, mats for ⁄ 2 -yard shovels are 12 to 14 feet wide, and for ⁄ 4 -yard, 14 to 18 feet. The
length should be about half the overall length of the crawlers, except that they should be shorter
if necessary to fit into the truck body that will have to carry them. If they are made for two sizes
of shovel, they must be strong enough for the large one, and short enough so as not to be too heavy
for the smaller machine.
Oak is quite generally used because of its strength and resistance to decay, and elm because of
its toughness. These hardwoods have the disadvantage that they cannot be nailed readily, so it is