Page 204 - Moving the Earth_ The Workbook of Excavation

DITCHING AND DEWATERING

5.6 THE WORK

FIGURE 5.4 Hydraulics make narrower connections.

pressure on the bucket will lift the rear wheels and push the tractor right out of a mud hole. Or the
bucket can pull it out backward, if that is what is needed.

Wide Ditches. When a ditch is to be more than one bucket width, one or both edges will be slightly
uneven because the bucket will move inward, toward the center pin of the shovel. Usually one side is
made straight by lining the shovel to that side, and by the hacking done on the other side. If neatness is
important, the ridges can be smoothed by drawing the bucket in while lightly swinging against the edge.
The full width of the ditch should be taken off in layers if it is to be dug from one position,
rather than cutting one side to depth then starting on the other.
If sloping beds of shale are encountered, digging should be arranged, if possible, so that the
bucket teeth will cut along the bedding planes. Shale dug in this manner at moderate depths is apt
to come up in sheets, so that the ditch will be widened irregularly.
Production. The rate of ditching depends on a number of variables, including depth and width of
the ditch, bucket size and efficiency, cycle time of the hoe, digging qualities of the soil, obstacles
and hazards both below and aboveground, presence of rock, accuracy of grade required, and need
to separate topsoil.
A ditch that is shallow, with soil piled on the edge, offers the fastest digging cycle, but the
bucket is not apt to fill well. Deeper digging slows the cycle and means more soil to move, but
allows better filling of the bucket. A narrow bucket does not fill as well as a wide one at any depth.
A ditch that is wider than the bucket takes much more time.
Boulders and heavy roots slow the digging. Presence of buried pipes or conduits that must not
be broken cause serious delays, particularly if their exact location is not known. Buildings or trees
that interfere with maneuvering cut down production, as does lack of space to pile spoil.
It takes much longer to clean an irregular rock surface for blasting than to dig a clean trench
to grade. Then there is the extra expense of drilling, blasting, and redigging.
The need to keep an accurate grade makes an operator work more slowly, and occasional stops
are needed to check gradient or depth, unless a laser-beam setup is used. A smooth bottom finish
is produced readily by a wrist-action bucket, but with some difficulty by a rigid one.
Stripping sod and topsoil separately will slow the digging from 5 to 30 percent.
When a trench needs to be braced during or immediately after the digging, production will be
determined by the rate at which bracing is set, which almost always is much slower than the digging.
Here’s an example of calculating digging rate: