Page 322 - Moving the Earth_ The Workbook of Excavation

LANDSCAPING AND AGRICULTURAL GRADING

7.16 THE WORK

Extra space may be provided in a turnaround for parking, or to supply peace of mind to uncer-
tain drivers.

Surfacing. Four inches of good bank gravel, crushed rock, shell, or similar materials should be
stable enough for a building drive on well-drained soil. Under average conditions 6 inches is
safer, and when the ground is soft and wet, 8 inches to 1 foot or more may be required.
A stone fill underneath can be used to reduce the gravel requirement. Any flat stones near the
surface should be set on edge so that they will not rock and disturb the top dressing.
If the driveway is long, it may pay to try to get by with a minimum depth and add more material
to any soft spots as they develop. However, it is often necessary to dig away the softened gravel,
as it mixed with mud underneath. If the driveway is short or the budget liberal, it is good practice
to put down a safe depth in the first place.
These materials may be used for both the bulk and the surface of the drive, may be given a surface
treatment, or may serve only as a base course.
If used alone, varying amounts of difficulty may be found with loose stones, gullies, dust, track-
ing small particles into buildings and cars, muddy surfaces, ruts or mudholes, or scattering on the
grass, depending on the kind and quality of material used and the circumstances.
Calcium chloride, either scattered on the surface or mixed in, will prevent the drive from
becoming dusty, and will help to hold it against washing and scattering. It should not be used in
the immediate vicinity of the building, where it might do damage if tracked in.
A thin layer of loose pebbles or fine crushed rock makes an attractive surface for light and
slow-moving traffic, but scatters under fast traffic. Snowplows are likely to move a large part of
it to the lawn.

AGRICULTURAL GRADING

NEED FOR GRADING

It is often necessary or desirable to regrade land in order to use it for farming. In arid regions, land
is leveled to permit even distribution of irrigation water. In semiarid climates, sloping land may
be terraced to hold rainfall behind dikes so that it will soak into the ground instead of flowing off.
Where the rainfall is adequate or excessive, terracing may be necessary to reduce washing of
soil from cultivated slopes. Under any conditions of climate or soil, leveling may be desirable to
allow use of large or high-speed machinery. Alone or in conjunction with underdrainage it may
increase yields by eliminating burning out of crops on ridges and drowning in hollows.
Agricultural grading differs from other types of earthmoving in the large areas to be treated in
proportion to the money available, the flexibility in engineering requirements to suit conditions
and cost factors, and the problems relating to the handling of topsoil.
Cuts and fills are typically shallow, vertical movement of soil is slight, and horizontal move-
ment is relatively great.

TERRACING

Terracing land is the grading process of interrupting slopes with ridges, channels, or benches, or com-
binations of them, in order to slow or stop the flow of rainwater and to prevent harmful soil erosion.
Terracing may serve to hold water on the slope so that it will soak into the ground; allow water
to flow off it while keeping the loss of soil to a minimum, or to reduce slopes so as to make them
more readily workable or irrigable.