Page 300 - Moving the Earth_ The Workbook of Excavation

PONDS AND EARTH DAMS

6.36 THE WORK

Dozer. If the bottom is firm enough to support a dozer, and if the mud is thick enough that a good
load will stay in front of the blade, a dozer may provide the fastest and cheapest cleaning job.
The mud can be skimmed off gravel subsoils with little mixing. On softer footings, or wet soils
which churn to mud readily, several inches may have to be taken with the mud. In any case, the
digging down need not be as deep as with dragline work.
Disposal of the spoil may be a critical problem. It is liable to be too sloppy to pile up high
enough for a bank, and to contain too much organic matter to make a satisfactory shore.
It can often be pushed out. The average pond edge is too steep for a dozer to climb with a load,
so a ramp or ramps must be cut in it (Fig. 6.24). If the shore is a dam, with low ground beyond, very
liquidy muds can be trapped in the ramp entrance and pushed through. Because of light friction,
a dozer may push five to ten times its normal yardage on each trip through the slot, but a part of
the volume will be water.
The ramp is apt to soften and break down, particularly at the bottom. Also, disposal areas at
its head may fill up rapidly. For this reason, a number of ramps are liable to be required, and back-
filling these later may be a major project.
The front-end loader, with grousers bolted on every fourth or fifth shoe on each track, is the
preferred tool for this work. The widely spaced cleats do not clog with mud. In cutting through
heavy deposits, a front-end loader is more adept at side casting than a standard dozer, and can
backdrag material out of bad spots. When this is done by filling the bucket, it may be necessary
to float it while backing to better ground, as lifting it tends to make the front of the machine sink
in. This machine can often unstick itself by using the bucket dump as a pushing or pulling device.
The second choice is a wide-gauge bulldozer. It usually has wide shoes that reduce its tendency
to sink, and the width gives extra leverage for turning with loads on slippery footing. If grousers
are worn down, a few of them can be built up to provide nonclogging traction.
When the bottom is reliably hard, a large dozer may be used. It is desirable because of greater
production in both the volume of mud moved and area left cleaned by a single pass. It can also back
into a deeper layer of soft mud without getting hung up than smaller machines with less clearance.
On soft or doubtful bottoms, lighter machines are much less apt to get stuck and are easier to
rescue if they do.
Saturated clay, silt, or very fine sand may look and act firm when work starts, but soften under
the weight and vibration of machinery. This change will be caused much more quickly by heavy
than by light units. However, such soil will often continue to give adequate support to a dozer as
long as it keeps moving, even after becoming too soft for comfortable walking. No machinery
should be left standing for any length of time, particularly if unattended.

FIGURE 6.24 Pushing mud up slot ramp.