Page 137 - Moving the Earth_ The Workbook of Excavation

ROCK, SOIL, AND MUD

ROCK, SOIL, AND MUD 3.31

usually ample space behind the pile so that the mud which moves in that direction makes a place
for more in the pile, and increases the amount of digging that can be done from one stand. The
effectiveness of the dike will of course depend on the quantity and type of dirt available for it.
If the dirt is being loaded in trucks, an effort should be made to get dry material on the bottom
to reduce trouble with the load sticking in the body. Most excavating in swamps and mud is done
by revolving excavators with dragline attachments.
Bulldozers. Bulldozers are not suited to wet excavation since they cannot work efficiently on
artificial supports. However, they can skim shallow layers of mud off hardpan and dig cautiously
in muds compact enough to give them some traction. In skimming work, it is usually best to start
at one side of the mud area and make a pass removing the mud cleanly. Each successive pass
should be to full depth and cut just enough into the side of the muck to fill the blade, without
allowing it to slop off the other side of the blade into the cleared area. The mud should be pushed
far back, as the dozer cannot climb up on it to make high piles, and there is danger of its flowing
back into the hole.
Wide-gauge dozers are preferred, as they usually have wider track shoes for greater flotation,
their weight is spread over a larger area, and they turn more readily on poor footing.
Cleats. Smooth or semigrouser tracks are unsatisfactory, as they have little traction on wet slip-
pery surfaces. In general, tracks with new and high grousers are better than those which are worn
and rounded. However, such grousers on loose soil will dig in very rapidly, and many muds will
pack in between them to make a new smooth surface even with their edges so that they become
ineffective.
The best solution for straight mud work where rocks or very hard subsoils are not involved is to
use flat shoes, with high grousers bolted on every fourth to sixth one. This should put two cleats on
each track under the machine at all times, and will give a good grip which will not clog.
A similar effect can be obtained by building up some of the cleats on a set of standard track
shoes, or replacing some shoes of a worn set with new ones.
A machine with cleats of variable lengths is likely to be almost incapable of working or traveling
on hard ground.
Dragline Road Cut. A permanent road should not be built over unstable mud unless absolutely
necessary. Such muds, particularly if rich in organic matter, will gradually be compressed and dis-
placed by the weight of the road, allowing it to sink unevenly. The mud should therefore be
removed down to firm bottom and replaced with clean fill if possible. If it is too deep, or other-
wise too difficult to move, measures must be taken to stabilize it, such as with geotextile fabric.
Shallow mud may be removed by a dragline working just ahead of the fill, and piling it to the
side. The rate at which the mud pushes back into the hole determines how far ahead the dragline
can be operated. A foot or two of mud liquefied by the mixing action of the dragline bucket is usu-
ally pushed out by the weight of the fill, but sliding in of the banks must be avoided.
Surface water should be diverted and sufficient pumps used to keep the hole fairly dry. This
enables the dragline operator to see to clean out the mud thoroughly without unnecessary digging
of firm soil, and will prevent the fill from being turned to mud as it slides down the front of the
slope. If the fill is too wide for the dragline to clear, it may be built out in sections.

MUD BLASTING FOR FILL SETTLEMENT
If the mud is too deep for available draglines to handle, or if it slumps into the excavation before
fill can be placed, or if there is not adequate equipment to keep the water out, blasting may be
resorted to.
Mud is easily blasted out of a limited area and spreads in a thin film over the landscape, leaving
no heaps to dispose of. If a nitroglycerin or other sensitive dynamite is used, the concussion from
one explosion may detonate other charges of dynamite in the mud nearby, without the necessity
of using additional caps. The process, called propagation, greatly simplifies mud blasting.