Page 101 - Moving the Earth_ The Workbook of Excavation

SURVEYS AND MEASUREMENTS

SURVEYS AND MEASUREMENTS 2.51

be reduced to 80 or 90 percent of bank volume. Measurement in the fill is described as compact-
ed yards, or yards after shrinkage.
volume in fill
Shrinkage factor
volume in bank

volume in fill

volume in loose yards swell factor
Shrinkage percent 1 shrinkage factor

Shrinkage may also occur in undisturbed soil on which fills are placed, particularly if 50 tons
plus superrollers are used. Such shrinkage may be calculated by the following formula, if more
exact information is lacking:
depth of compaction shrinkage percent
Settlement
2
This is just an averaging of maximum compaction at the top and zero compaction just below
where the effect is felt. This depth would be about 48 inches in a clay loam soil under a 50-ton
roller. Such soil may have a shrinkage factor of .2, so by this formula
48 0.2 9.6
Settlement, inches 4.8
2 2
In wet conditions, or on steep slopes, displacement of subgrade material to the side may reduce
its useful bulk much more than its compaction does.
Exceptional Soils. Soils composed of volcanic ash or pumice, and soils built up by streams on
flats in arid regions, may show very peculiar behavior. Particularly, they may show excessive
compaction, sometimes to 40 percent of bank volume. In some cases, they even show shrinkage
during digging, so that loose yards are heavier than bank yards.
Such soils are found only in limited areas where contractors may be aware of their possibili-
ties. However, they constitute a hazard for the estimator, and any indication of their existence on
a job should be carefully checked.
One western state highway department in the United States has adopted a policy of paying for
highway borrow by weight rather than by volume to avoid unpleasant surprises for either the bud-
get or the contractor when such materials appear in borrow pits. The necessity of measurement
before starting work is avoided also. Portable truck scales that can be set up in a few minutes are
used for measurement of pay quantities.

CONTAINERS

“Container” is used here as a broad term to include transporting boxes such as truck bodies, dig-
ging and carrying buckets or bowls as in shovels and scrapers, and digging and pushing blades on
dozers and graders. But it does not include belts or pipes.

Measurement. Most buckets and bodies are rated by the manufacturer as to carrying capacity
in loose yards. This rating may be water level (the yardage of liquid which could be carried if it
did not leak out), line of plate or struck measure, which is water level plus any space between parts
of the rim which project above its low point, or heaped.
Shovel dipper buckets and highway truck bodies are normally rated at water level, carrying
scrapers and off-the-road trucks at both struck and heaped measure, and clamshells at water level,
line of plate and heaped.