Page 334 - Moving the Earth_ The Workbook of Excavation

LANDSCAPING AND AGRICULTURAL GRADING

7.28 THE WORK

FIGURE 7.20 One-level and bench grading.

If the maximum practical gradient is not sufficient to move the water the length of the field,
additional distribution lines can be installed. See Fig. 7.20. Very porous soils require pipes and
sprinklers.
Figuring Gradients. Earthmoving should be kept to a minimum to save money and to conserve
topsoil. If conditions justify the use of any one of several slopes, the one will be chosen which
conforms most closely to the natural topography.
If the steepest possible gradient is so much flatter than the original grade that excessive earth-
moving will be required, because of deep cuts at the top and high fills at the bottom, the field may
be divided into two or more levels or benches. These will have the desired slope and will be sepa-
rated by steep banks. A separate waterline is required for each bench.
The high corner or end of the field must be below the level of water in the ditch or its head in
the standpipe.
The new gradient must usually be placed at a level, or levels, where cut and fill will balance,
as cost may be greatly increased by bringing in borrow or dumping surplus soil. After the surround-
ing areas are largely under cultivation, borrow or disposal may not be possible.
Topsoil is not a problem in many arid valleys where soil is fertile to a considerable depth.
However, when topsoil is thin and rests on layers of soil which are infertile or hard to work, or when
the surface soil differs sharply in character from that underlying it, the cuts should be kept shallow.

Stakes. Stakes set in a square grid at 100-foot intervals, and on high and low spots, are used in
measuring the original surface and for marking the new grade. One or more benchmarks are set
outside the grading area, as discussed in Chap. 2.
The new grades are marked on the stakes in any convenient manner. On fills, time may be
saved by tying strips of cloth on grade lines to enable operators to see them without getting off
their machines. Where soils are loose, two stakes may be used to advantage—one hammered
down to ground level, the other left to project 2 or more feet. Cut and fill are figured from the top
of the lower stake and marked on the upper one.
Clearing. Much of the growth in arid regions is of a light and brittle character which breaks up
during grading and mixes with the soil, and has value as a binder and a source of plant food that
is more important than the slight difficulties it causes during finishing. This group includes the
various kinds of sage, tumbleweed, and many of the smaller cacti.