Page 105 - Moving the Earth_ The Workbook of Excavation

SURVEYS AND MEASUREMENTS

SURVEYS AND MEASUREMENTS 2.55

1
1
For example, a ⁄ 2 -yard backhoe might dig a ditch section 2 ⁄ 2 feet wide, 6 feet deep and 12 feet
long in 25 cycles, removing 180 cubic feet or 6.67 cubic yards bank measure. Dividing 6.67 by 25,
we have an average bucket load of .267 yard. Since the rated capacity of the bucket is .5 yard, we have
.267
CEF (bank yards) .534
.5
The efficiency factor in loose yards would be greater by the percentage of swell. In clay loam
with 20 percent swell (see below) the loose yards would be 6.67 1.20, or 8.0. Dividing by 25
cycles, we would have an average load of .32 loose yard. Then
.32
CEF (loose yards) .64
.5
It is important to always specify whether any container efficiency factor is for loose yards or
bank yards. One may be readily converted to the other, the loose yards figure almost always being
the larger, as it is increased by the percentage of swell.

OUTPUT

Work Cycles. The work cycle may be timed as a whole in figuring output for existing condi-
tions. For accuracy it is necessary to take the average of a large number of passes as there may be
a considerable variation among them.
If a study is made of a cycle, either to find a way to speed it up, or to use its time intervals as
a basis for figuring production under different conditions, it can be broken down into individual
operations which are timed separately.
A study of bulldozer and of scraper operation may include some or all of the divisions listed
below. Each one should be timed. Digging and traveling distances should be measured. A record
should be made of all grades, as these machines are much less efficient going uphill than downhill.

Bulldozer Scraper
Dig Load
Shift into second Shift
Transport Transport
Dump Shift
Shift to reverse (raise blade) Spread
Shift
Return Deadhead to turn
Shift to low (lower blade) Turn
Return to digging area
Deadhead to turn
Turn
Get to loading position
Shift into low
Wait for pusher

Machine Efficiency. Nonworking time such as delays for moving the machine, minor repair adjustment,
rest, getting instructions, or looking at grade stakes is not averaged into cycle time. It is considered sep-
arately as the efficiency factor of the machine. It may work out between 70 and 85 percent for short peri-
ods with expert operators on a properly run job, with machinery in good condition and weather favorable.
A convenient way of making rule-of-thumb allowance for efficiency of about 83 percent is to
consider that 1 hour contains only 50 working minutes. On this basis, a machine with a 30-second
cycle cannot be expected to perform it more than 100 times per hour.