Page 373 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

ROADWAYS 8.35

FIGURE 8.25 Taking off a hill.

This dirt can be utilized to build up the fill where it meets the cut, by allowing the bowl to drag
slightly until the fill is reached. However, dragging may cause a loss of speed which outweighs
the importance of the dirt moved.
Care should be taken not to cut below grade at the junction with the fill unless it is necessary
to make a ramp.
Turns. The time consumed in making a U turn with a scraper may vary from 5 to 60 seconds or
more, depending on space available, ground conditions, type of machine, traffic, and operator.
Fifteen seconds is a fair average.
Time consumed deadheading from the working area to the turn and back may be considered
part of either the turn or the haul, but it is better practice to consider it a separate part of the cycle.
On short hauls, turns and deadhead time have an important effect on production. As hauls
become longer, their significance decreases.
There are four major patterns of scraper operation, which are shown in Fig. 8.26. In the first,
(A) and (B), there are two turns to each dig-dump cycle; in the second, (C) and (D), one; and in
(E), one-half. Figure 8.26(F), with no U turns, is only practical when a very wide area, such as a
field or runway, is being graded.
When both cut and fill are wide enough for easy turns, the (C) and (D) layouts may be most efficient,
particularly when work areas are long and tractor speeds low. The advantage is that the scraper can turn
to start a new cycle immediately after digging or dumping. The length of haul can therefore be figured
between the centers of mass of the cut and the fill, as the longer and shorter runs will average out.
The diagram and arithmetic in Fig. 8.27 indicate the advantage of operating one cut with one
fill under low-speed conditions, and combining them when travel speeds are higher.
If turns cannot be made immediately at the end of the work, the time required to travel the aver-
age distance from the ends of spreading runs, and from the beginning of cuts to their turns, must
be added to the cycles, as in Fig. 8.28.
Through-travel highway patterns, seen in Fig. 8.26(E), have their greatest use where the graded area
is too narrow for turns, and cuts and fills are rather short and closely spaced. Their efficiency depends on
the extra time required for through travel, compared with that used for turns and deadheading.
Turn patterns are of course subject to the overall plan for the job, which may include some very
complex factors of distribution, work sequence, and separating of different types of soil.
These examples are somewhat oversimplified for demonstration purposes.

Turnarounds. The location of the turnaround in a narrow one-way cut is affected by the diffi-
culty of making it. For efficiency, it should be slightly across the hillcrest from the fill, so that the