Page 335 - Moving the Earth_ The Workbook of Excavation

LANDSCAPING AND AGRICULTURAL GRADING

LANDSCAPING AND AGRICULTURAL GRADING 7.29

However, larger shrubs and trees such as mesquite, greasewood, and acacia, the presence of
which often indicates good soil, are tough and deeply rooted, and their removal requires heavy
machinery. In thick stands of these plants, clearing is more expensive than grading.
Such growth can usually be piled and burned immediately after removal. The leaves and sapwood
are resinous, and the dry soil sifts out of the piles so that they burn readily. Heavy trunks are more
difficult to ignite, and if only a few are present, it may be easier to haul them to a dump.
Clearing methods and machinery are discussed in Chaps. 1 and 21.
Savings may be effected by cutting the trees flush with the ground wherever the fill will be deep
enough to permit tilling over them. However this is not recommended, as it will prohibit the future
use of pan breakers or other deep tillage tools and will add greatly to the expense of installing under-
drains if they should become necessary. The same objection applies to burying logs in the fills.
Wind Damage. Clearing and grading should not be started until irrigation water is available. The
native vegetation, even when very sparse, has some power to break the wind and hold the soil.
The weathered ground surface usually has a crust which resists wind scour. These natural protections
are destroyed by the work, and unless water can be put on and a holding crop started immediately,
the best part of the soil may be blown away or piled into dunes that may be more costly to level
than the original surface.
Wind damage during the work may often be avoided by choosing a season in which wind-
storms are infrequent. If this is not possible, the final leveling and planing should follow imme-
diately behind the rough grade, as a perfectly smooth surface is much more resistant to scour and
dune formation than one having ridges or tracks of machinery on it.
If such a planed surface becomes roughened by wind, it should be replaned before the next
storm, and kept flattened until a crop can be grown.
Machinery. Dozers are used to clear, to take the tops off ridges and dunes, to bevel steep slopes,
and to fill in pits; for cut-and-fill work on short pushes; and for pusher work with scrapers.
A drag leveler can be used to smooth out rough spots wherever it is possible to walk the tractor
over them. It can transport soil long distances, although its efficiency diminishes rapidly over 200
feet. Compared with the dozer, it has the advantage of making a wider cut, with little tendency
toward scalloping, and has a greater transporting capacity and speed. Compared with scrapers, it
has greater stability against overturning, smooths a wider area with each pass, cuts down and fills
more quickly, and can be dumped promptly if the tractor gets stuck. It has a smaller transporting
capacity and generally will not make as smooth a grade.
On any large area, the bulk of the dirt moving is most efficiently done with scrapers. Because
of the width of most of these grading jobs, and the small slope of the land, these can be used in
almost any pattern preferred by the supervisor or operators.
Grading. One technique is to produce a rough finish grade in the high corner of the field and to
expand this grade as continuously as possible. Where necessary, spot grading operations are done
beyond this area in order to secure fill or to dispose of surplus.
Economies may be effected by loading the scrapers toward adjoining depressions so that the
soil pushed along in their efforts to load will fill them. If the soil is very loose, this may be more
important than loading in the direction of the dump, but it is often possible to do both.
Fills are usually made in thin layers in order to get maximum compaction from hauling equip-
ment, as rollers are seldom used. Tamping rollers will produce a more permanent grade where fills
of more than a foot or two are required, but close competition for the work may not permit the
necessary increase in price.
Rough-graded sections may be settled by flooding before doing finish work.
It is often possible to keep the short-range equipment, dozers and drag scrapers, working all
the way through the job if the area contains a number of adjacent humps and hollows. The drag
level can also do the light finishing more economically than the scrapers.

Finishing Off. As soon as any considerable section is rough-finished, grades are rechecked and
additional stakes may be placed. These can be on 50-foot centers both ways, or 50 feet one way