Page 275 - Moving the Earth_ The Workbook of Excavation

PONDS AND EARTH DAMS

PONDS AND EARTH DAMS 6.11

they must handle material more often to move it the same distance; cannot dig as deep or pile as
high or penetrate hard material or take out stumps as effectively as larger machines; and cost more
for each yard of digging.
Small draglines may be equipped with long booms to match the reach of large machines, but
this reduces their speed and may interfere with stability. Additional counterweight is advisable,
and the inertia of this and the reduced leverage on the bucket load cause it to take more time to
start and stop each swing, increasing the cycle time by 1 to 5 percent for each foot of boom added.
If the swing clutches or engine power is barely adequate to manage a standard boom, loss of time
through excessive slipping or lugging down will be much greater than with a high-powered
machine of the same rated capacity.
Undersized buckets are often used with extralong booms. These reduce the tendency to tip, and
speed up the cycle somewhat, but reduce the payload and the ability to penetrate hard soil.
Digging Cycles. A three-quarter-yard dragline with a 40-foot boom digging at the end of its
reach, and swinging 180° to dump, can move part of the material 70 or more feet at each handling and
complete two to three digging cycles a minute. The same machine, in digging up its own track, may
move the dirt only 10 to 20 feet at the rate of three to four buckets a minute. The average distance
the soil is moved may be found by measuring from the middle of the cut to the middle of the pile.
If the spoil is to be moved back through several handlings by the dragline, the long move is
desirable; but if it is being stockpiled, the short, quick cycle is best. Most digging patterns include
both long and short swings, to get maximum work out of minimum walking.
Building Up Ends. If fill is needed at the upper and lower ends of a pond, the dragline may dig
and pile in a curve as it rounds the ends, as in Fig. 6.2. Another method is to make straight cuts
across the ends, as in Fig. 6.8. Such work at the outlet will block the drainage ditch, or interfere with
pumping, so that it should be the last spot to be dug.
Drainage may be maintained by laying pipe in the ditch before covering it. If the spoil is to be
spread after the first cut, such pipe may be left permanently, being fitted with a cap or valve so that
it may be blocked to fill the pond, or opened to drain it. If two or more handlings of the spoil are nec-
essary, temporary pipe must be placed and then lifted as the digging progresses, for which purpose
corrugated steel is most satisfactory because of ease of handling and resistance to rough treatment.

Islands. Both the quantity and difficulty of digging can often be greatly reduced by building islands.
In cases where a shallow cut is made, and the balance of the depth obtained by building a dam, most
of the spoil can be disposed of in islands. If cutting is deep, some soil may still be piled on them and
their bases do not have to be excavated.

FIGURE 6.8 Straight-end cuts.