economical haul distance is the mass diagram
method.
A mass diagram is a graph or curve on which the
algebraic sums of cuts and fills are plotted against
linear distance. Before these cuts and fills are
tabulated, the swells and compaction factors are
considered in computing the yardage. Earthwork that
is in place will yield more yardage when excavated
and less yardage when being compacted. An example
of this is sand: 100 cubic yards in place yields 111
cubic yards loose and only 95 cubic yards when
compacted. Table 10-1 lists conversion factors for
various types of soils. These factors should be used
when you are preparing a table of cumulative yardage
for a mass diagram. Cuts are indicated by a rise in the
curve and are considered positive; fills are indicated
by a drop in the curve and are considered negative.
The yardage between any pair of stations can be
determined by inspection. This feature makes the mass
diagram a great help in the attempt to balance cuts and
fills within the limits of economic haul.
The limit of economic haul is reached when the
cost of haul and the cost of excavation become equal.
Beyond that point it is cheaper to waste the cut from
one place and to fill the adjacent hollow with material
taken from a nearby borrow pit. The limit of economic
haul will, of course, vary at different stations on the
project, depending on the nature of the terrain, the
availability of equipment, the type of material,
accessibility, availability of manpower, and other
considerations.
The term free-haul distance means a distance over
which hauling material involves no extra cost. This
distance is usually taken to be about 500 feet–
meaning that it is only for hauls longer than 500 feet
that the limits of economic haul need to be considered.
Table 10-1.—Soil Conversion Factors (Conversion Factors for Earth-Volume Change)
10-11
