Agriculture Reference
In-Depth Information
When going through the process of calculating earthwork quanti-
ties, keep in mind that there is a factor that often contributes to over- or
underestimating these quantities. The factor has to do with shrink-
swell. The undisturbed soils on a project site are generally dense, having
been in place for hundreds, thousands, and more years, going through
daily and seasonal cycles of rain and sun, giving the soils ample time to
consolidate and become dense. One only has to take a shovel and begin
digging a hole to understand how the existing soils can be somewhat
difficult to penetrate. Some soils are more dense and thus more difficult
than other soil types. Next, after digging a hole, shovel the removed soil
back into the hole, and you will find there is an excess of soil after the
hole has been filled. By compacting the soil as you shovel it in, you can
replace most of the removed soil, but often an amount on the order of
10 percent is left, with no more room in the hole for any more soil. This
same concept is experienced when doing earthwork on a site. Even after
making careful cut and fill calculations, the landscape architect may
find an excess amount of soil remaining after the contractor has com-
pleted most of the earthwork. As one goes about the process of calculat-
ing the quantities of cut and fill of a site grading plan, an excess of 10-25
percent may occur during the actual earthwork operations. Consider 10
percent for sand and sandy soils, and as much as 25 percent for common
earth. Rock removed may result in as much
as 65 to 70 percent overage—that is, rock
that is removed can produce a quantity 165
percent of the quantity calculated from the
site-grading plan unless it is crushed into
finer material.
To start, consider the grading diagrams
in Figures 15.2-A and 15.2-B. Dashed contour
lines represent the existing topography,
and the solid lines represent the proposed
contours. The solid proposed contours that
move downhill from the original contour
location represent fill. Note that an upper
69
68
Fil
67
66
65
Cut
66.5
Level
Area
64
63
62
61
60
20 Scale
Figure 15.3
Grading plan diagram for creating a level
shelf area
