Page 47 - Moving the Earth_ The Workbook of Excavation

LAND CLEARING AND CONTROLS

LAND CLEARING AND CONTROLS 1.47

BOULDERS AND BUILDINGS

Boulders. An area may be so strewn with loose or partially buried boulders that work is diffi-
cult, and the removal of these rocks may properly be considered clearing.
If large enough machinery and suitable disposal points are available, the rocks may be turned
or dug out and pushed away. If they are too large for easy handling and disposal, they should be
broken up.
Breaking may be done by blockhole or mudcap blasting, backhoe-mounted demolition hammers,
drilling followed by plug and feathers splitting, or a muscle-operated sledgehammer. See Fig. 1.37.
A plug and feathers set consists of a pair of half-cylinders (feathers) with outer surfaces fitting
in a drilled hole, with inner faces shaped for driving a thin steel wedge (plug) between them by
air or hand hammer, or by hydraulic pressure.
The very gradual taper of wedge and cylinder halves causes blows or pressure on the plug to
be converted into a tremendous sideward pressure, which can split large boulders and break off
chunks of bedrock.
Under many circumstances, however, a contractor may prefer to get rid of the rocks by dig-
ging and pushing. The dozer is the standard tool for this work. Efficiency can be increased by use
of a tilting blade, a dozer shovel bucket, a stumper, or a heavy-duty rake blade.
A dozer can move quite a large rock on firm ground, perhaps several times its own weight. If
the stone is too large for direct pushing, it can be pushed first on one side, then on the other, as in
Fig. 1.38. If it is rounded, it can be rolled by lifting the blade while pushing. If the blade does not
have enough lift to control it over, it can hold it in a partially rolled position, with locked brakes,
while the stone is blocked up. The blade may then be lowered and the push and lift repeated.
Partly buried rocks may be pushed or dug out in somewhat the same manner as stumps. The resis-
tance they offer is usually more rigid than that of stumps, and if a rock will shake in the first few

FIGURE 1.37 Boulder split by plug, hydraulic-powered.