Page 135 - Moving the Earth_ The Workbook of Excavation

ROCK, SOIL, AND MUD

ROCK, SOIL, AND MUD 3.29

FIGURE 3.20 Support by roots and poles.

In a swamp studded with stumps, or rock, platforms break up very readily. The spaced plank
type, which is generally preferred because of light weight and reduced suction, will break if used
across a stump or heavy buttress root, and the heavier types will strain and splinter. Some operators
prefer to pull the stumps before walking over the spot, thus exchanging the platform-breaking
obstacles for a wet and uncertain footing.
It is dangerous to move a machine onto platforms which are placed with one side on firm
ground and the other side in loose mud. The mud side may sink enough to cause the shovel to slide
to that end and tip over. The soft side may be braced with platforms or logs, or the firm side can
be ripped up, before placing the platforms.

Poles. A shovel may be walked and worked on fairly soft footing by the use of saplings instead
of platforms. These should be of firm wood, preferably green, 2 to 10 inches in diameter, and long
enough to project 2 or more feet beyond the tracks on each side.
An extra precaution is to place outrigger poles under their ends, parallel to and outside of the
machine’s path. When the shovel has passed over the poles, they may be retrieved and used again,
but the mortality rate usually is high, particularly among softwoods.
When the shovel is working, it will often be found that a pole or two under the front, or where
the lifting of the load is done, will suffice to support it. With worse conditions, more cross poles
and outrigger poles should be used.
If long poles are not available, short ones may be used, centered under each track, but they are not
nearly as satisfactory. There is a danger that they might tip under the shovel and jam into the machinery.

WET DIGGING

In any extensive wet digging, draining or surface pumping is liable to leave a sheet of at least a
few inches of water on the bottom. This is a convenience in establishing a flat bottom grade, but
unless special precautions are taken, large quantities of water will be dug out along with the soil.
This water may run directly back into the hole, in which case the time and fuel used in lifting
it are wasted. If it mixes with soil, either in the bucket or in the pile, it will tend to liquefy so that
the spoil will not stand in the high, steep-sided piles which afford maximum dragline production.