Page 125 - Moving the Earth_ The Workbook of Excavation

ROCK, SOIL, AND MUD

ROCK, SOIL, AND MUD 3.19

EQUIPMENT FOR MUD

Mud trouble can be reduced by using proper equipment. In general, crawlers are preferable to
wheels; tracks should be the longest and widest obtainable, tires should be big, soft, and cleated;
and units should be the smallest that will do the work. All-wheel-drive is desirable for trucks.
Articulated dump trucks with six drive wheels work well in muddy soils.
The ability of a machine to stay on top of soft ground is affected by its ground pressure, which
is usually measured in terms of pounds of weight on each square inch of ground contact; shear,
which is the load on the edge of the track or tire; and total weight.
Ground pressure is the most important factor in loose soils such as sand or dust. Shear is most
important when a soft soil is protected by a harder crust or sod. It is increased when the machine is
tipped, and when it pushes a load. Total weight affects deep mud, which may creep or flow from under
the machine.
Grousers, cleats, and tire chains cut and churn up their footing but are necessary to get a grip
on slippery surfaces.
Some wheel tractors can be fitted with temporary metal and rubber tracks which enable them
to work in fairly soft places.
Special vehicles, such as the military weasel and the swamp buggies used for exploration by
oil crews, are very useful in supplying fuel and other essentials to machinery working in swamps.

TEMPORARY ROADS

Wheeled Equipment. Wheeled equipment is best kept out of swamps unless they are frozen,
dried out artificially or by drought, or have roads built into them, perhaps with geotextile fabric.
The use of geotextile sheeting is shown in Fig. 3.12, where a roadway with moderate rutting of
the subgrade when dry would become impassable when it rains. The minimum road is a strip in
which the soft spots are stuffed with brush or bridged with planks. If poles are used, they should
be closely fastened so that they cannot work apart and let wheels down between. Whenever pos-
sible, surface poles should be at right angles to the direction of travel.

Pole Tracks. Poles may also be used as tracks to be straddled by dual wheels. They should be
straight, free of stubs or sharp projections which might cut tires, and large enough that they cannot
pass between the tires toward the hub and small enough that they will not slip sideways out of the
groove between the tires. The poles should be overlapped at their ends so that the wheels will not
be left without support while passing from one to another.
Front wheels may be placed on skids or runners and chained down. If the mud is not very deep,
they may be left to make their own way.
This procedure is for short emergency moves only.

Corduroy. A corduroy road can be built to support heavy machinery on very soft ground. It con-
sists of logs or half logs laid across the traveled way, touching each other. They may be laid directly
on the ground, on one or more stringers running lengthwise, or on both stringers and longer cross
logs, called sleepers. Several constructions are shown in Fig. 3.13.
A minimum width of 12 feet is recommended for one-way traffic, although it might be possible
to get by with 10 feet. Curves should be 2 to 4 feet wider. Cross logs may be extended beyond the
road edge for additional stability.
Logs 6 to 10 inches in diameter are generally strong enough for the work, without being exces-
sively heavy. Thinner ones may be used as stringers. Heavier sizes may be split for cross logs, or
partly buried for stringers.
The upper surface of cross logs should be smoothed by removal of stubs and bumps, and per-
haps by planing down with adze, axe, or ripsaw.
Guard logs are desirable to prevent vehicles from sliding off, to reinforce the road structure,
and to retain any surfacing which may be added. Picket stakes may be placed to hold guards in
position, and to bind cross logs to the outer stringers. Edges may be bound together by heavy wire,