Page 97 - Moving the Earth_ The Workbook of Excavation

SURVEYS AND MEASUREMENTS

SURVEYS AND MEASUREMENTS 2.47

Measurements are sometimes given in feet and inches. A cubic inch is too small a unit to be used
for dirt (it takes 1,728 of them to make a cubic foot, 46,656 of them to make a cubic yard), but it is
used in measurements of engine and compressor displacement and other mechanical descriptions.
It is difficult to multiply feet and inches by feet and inches, so the inches are expressed as
1
2
either regular or decimal fractions of feet. Regular fractions ( ⁄ 3 , ⁄ 12 , etc.) are more accurate, dec-
imals are more convenient.
Weight. In highway jobs, cellar excavation, and site preparation the estimator is chiefly inter-
ested in the bulk and digging characteristics of the material to be moved. Its weight has impor-
tance chiefly in figuring loading and gradability of haulers, and is only occasionally used as the
basis for estimating. See Fig. 3.5.
In mines and quarries weight is likely to be a more important factor than bulk. Products such as
coal, crushed stone, cement, ores, and ore concentrates are usually sold by weight, and therefore
are measured by weight as they are dug. There are exceptions, however. Some open-pit mines com-
pute their operations on a yardage basis. Others figure ore by the ton and overburden by the yard.
The standard weight measurement is the short ton of 2,000 pounds. There is also a long ton of
2,240 pounds that is used in some mines. It should always be specified as a long ton, and the
unmodified word “ton” should mean short ton only.
Other measures are the hundredweight of 100 pounds, and the British stone that weighs 14
pounds. In the metric system a kilogram, often called a kilo, is 2.2046 pounds, say 2.2 for short.
A metric ton is 1,000 kilograms, or 2,204.6 pounds, about 10 percent more weight than in a short
ton, and a little less than a long ton.
Area. In many operations, bulk and weight do not provide a suitable basis for measuring the
amount of work. For example, with any given land-clearing condition, the time and cost of the
work vary with the area. Clearing is usually measured by the acre, which is 43,560 square feet or
4,840 square yards. Many estimators do their figuring in acres of 40,000 square feet to simplify
arithmetic, and make allowance afterward for the difference of almost 10 percent.
Grading land where cuts and fills are shallow is likely to show costs in relation to area rather
than bulk of soil to be moved. But when cuts and fills are deep, bulk becomes more important than
area. Exact grade requirements increase grading costs in proportion to area. The estimator must
keep track of these factors.
Topsoiling and seeding are figured mostly on the basis of area, although of course the depth
of topsoil and the heaviness of seeding are important in determining the rate per square yard.
In the metric system the square yard is replaced by the square meter. This contains 10.76 square feet
or 1.196 (say 1.2) square yards. The next larger measure is the “are” that contains 100 square meters,
119.6 square yards, or .0247 acre. Then there is the hectare, that contains 10,000 square meters, 11,960
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square yards, or 2.451 (say 2 ⁄ 2 ) acres. The largest measurement is the square kilometer, 1,000,000 square
2
meters, 245.1 acres, or .3861 (say ⁄ 5 ) square mile.
Lineal Measurement. Work such as ditching, installing pipe, tile, and fencing is measured by
the lineal or running foot, yard, or mile. There are 3 feet in a yard, and 5,280 feet or 1,760 yards
in a mile. Metric measures are the meter, 39.37 inches, 3.28 feet, or 1.09 yards; and the kilome-
3
ter, that is 1,000 meters, 3,281 feet, 1,094 yards, or .6212 (slightly more than ⁄ 5 ) mile.
From both a time and cost viewpoint it is of course necessary to know also the width and depth of the
ditch, the soil and other special conditions, the size and type of pipe, and the type and quality of fencing.
Drilling is usually measured by the lineal foot, with the size of hole specified.

TYPES OF PRODUCTION

A construction machine may work in an intermittent cycle, in a continuous flow, or in ways that are inter-
mediate between the two types. Figure 2.43 shows the category in which various types of equipment fall.