Page 5 - Moving the Earth_ The Workbook of Excavation

LAND CLEARING AND CONTROLS

LAND CLEARING AND CONTROLS 1.5

In any soil, one stump can be packed in more solidly than a number of them. A common practice,
when there are just a few big stumps, is to dig out each one with a backhoe, dig the hole deeper, put
the stump back in it, and backfill. This shortcut is often not on the plans, and may cause surprise and
dismay later, when the surface settles or a small machine tries to dig a trench through the area.

Burning. Where burial is not practical, burning is usually the most efficient method of disposal
and does the least long-range damage to the environment. Most of the discussions in this chapter
are based on the presumption that fire will be used.
However, since open burning is prohibited or severely restricted in an increasing number of
states and localities, it is worthwhile to examine the relative advantages and disadvantages of fire
compared with other methods of disposal.
It will be assumed that burning is handled by reasonably experienced crews, with proper
regard for safety and confinement of the fire to the vegetation being cleared.
Piles of brush or trees usually contain one-fifth to one-tenth solid matter, the rest being air
space. These solids average at least half water, and most of their dry weight is cellulose, lignin,
and other burnables. The ash that is left after efficient burning is only a few percent of the dry
matter (exact figures are difficult to obtain). A good fire will therefore reduce the vegetation to a
small fraction of a percent of the original bulk.
The ash residue is too fine to be good fill material, but its quantity is so insignificant that it can
usually be incorporated in other soils, or pushed aside, without difficulty.
It may be reasonably held that efficient burning results in the total removal of cut and uprooted
vegetation.
Soil under a hot fire is rendered unfit for supporting growth for 1 to 3 years, but can be restored
by plowing or ripping, and fertilizing.
A fire in dry material, with plenty of air, will burn mostly with hot clean flames, which pro-
duce carbon dioxide and water vapor, with few pollutants. Green wood and leaves, wet or dirty
piles, and most weakly burning fires will give off large amounts of smoke, containing variable
quantities of methanol, methane, acetic acid, tars and oils, and carbon monoxide.
Such fires, if upwind from inhabited areas, may create an extreme local nuisance, but its dura-
tion is very short. It is doubtful if the pollutants they put into the atmosphere equal those that
would have been discharged during the natural lifetime of the plants themselves if they had not
been destroyed. The burning concentrates them into a few hours or days.
The pollution problem that faces the world does not arise from country areas or from any activ-
ities (including open fires) normally conducted in them. It is a problem of cities, factories, and
internal combustion engines.
It is therefore quite unreasonable that burning should come under total or almost total bans, while
the real offenders are usually let off with moderate percentage reductions of their offensiveness.
Regulations against burning are costly. Substitute means of disposal, which are discussed in
following sections, are more expensive under most circumstances, require vastly increased con-
sumption of fuel, and may create environmental problems of long duration. The extra cost in highway
construction alone is probably already in the tens of millions of dollars a year.
Clearing by hand in cold weather may be practical only in the presence of hot fires, for both their
emotional uplift and their actual prevention of acute discomfort, including frostbite. Even without
need for heat, there is little satisfaction in clearing brushy land if the debris must be left to litter
the ground, making it dangerous for people and animals; or heaped into unsightly piles that take
years to rot. And loss of unfarmed and unmowed fields to brush is a serious and increasing eco-
logical problem.
The cost of buying or renting shredding equipment, noise, fueling problem, and danger to inexpe-
rienced operators put these machines out of reach of most people who wish to do their own clearing.
Chipping. Brush, saplings, and even big trees may be fed into machines that reduce them to chips of
small and fairly regular size, by action of a rotating toothed drum (see Fig. 1.1). These chips may be
scattered or piled in the work area, or fed through a chute into dump trucks.
A small machine can be towed behind a pickup truck, and often maneuvered on the job by
hand. It is hand-fed with bundles of brush, and with saplings up to 3 or 4 inches diameter.