Page 106 - Moving the Earth_ The Workbook of Excavation

SURVEYS AND MEASUREMENTS

2.56 THE WORK

If two machines are interdependent, the efficiency factor is usually lower so far as the job is
concerned. If two 80 percent efficient machines are down at the same time every time, the effi-
ciency factor remains at 80 percent. If they are down separately each time, the factor drops to 60
percent.
As the period under study becomes longer, efficiency drops steadily, as weather, work
sequence stoppages, and major overhauls must be considered. Time losses can be further
increased by inefficient management, bad pit layout, poor morale of employees, or other unfa-
vorable conditions.
Output Formulas. A formula which can be used for figuring production of any machine with a
regular cycle is
Q K E 60 f
Output, yards per hour
C
m
where Q capacity, either struck or heaped
K efficiency factor of bucket or body
E efficiency factor of machine
60 minutes in 1 hour
f soil conversion factor
C cycle time, minutes
m
If the result is to be in bank yards, f has a value obtained from observed swell, or from Fig.
2.44. If the result is to be in loose yards, f equals 1, and can be dropped from the equation. The
4
factor K is not required when full, solid loads can be taken. If efficiency is approximated at ⁄ 5 ,
then 50 minutes are used instead of 60, for the hour.
Under these conditions, the following simplified formula can be used:
Q 50
Output, loose yards per hour
C
m
If a 45-minute hour is used, this formula is
Q 45
Output, loose yards per hour
C
m
When timing machines have a cycle less than a minute, it is more convenient to figure it in sec-
onds. This is done by multiplying the number of minutes by 60, and using C —cycle time in sec-
s
onds—instead of C . With these substitutions, the formula will be
m
Q K E 3600 f
Output, yards per hour
C
s
Or simplified for a 50-minute hour to
Q 3000
Output, loose yards per hour
C
s
For a 45-minute hour we would have
Q 2700
Output, loose yards per hour
C
s
Additional data on output will be found in Chap. 11 and the Appendix, and included in dis-
cussions of particular machines.