Page 195 - Moving the Earth_ The Workbook of Excavation

BASEMENTS

BASEMENTS 4.35

Boulders may be loaded into a truck by a hoe or a loader, or more gently by a clamshell, grapple,
or crane. For crane work, the rock must be firmly gripped by chains or slings.
Chains should be of the lightest size that will lift the weight, as a thin chain grips rock much
more closely than a thick one. Undersize chains break frequently, and spares and repair links and
hooks should be kept on hand.
Alloy chains are expensive but are small and light in proportion to strength.
Small cables grip rock well but wear and fray rapidly, so that sharp ends of broken wires make
them dangerous to handle.
Slings may be made of several strands of light cable or chain, and combine the grip of small
sizes with the strength of large ones.
Boulders may be broken by blasting, but in city areas mud capping is not permissible. Splitting
may also be done with sledge hammers, air hammers, or drills and plug-and-feather sets.

HILLSIDE SITES

Downslope. So far we have considered excavation in a level plot. As the basement depth is cal-
culated from street or sidewalk level, a downward pitch to the rear would decrease the amount of
excavation, and an upward one would increase it.
If the lot slopes down to the north, as in Fig. 4.29, the natural grade can be cut to the proper
slope for a ramp by a bulldozer, and the material removed used to build a flat shelf at the first cut-
ting level on which the front shovel and trucks can start work. If insufficient dirt is cut in making
the ramp, the shovel can dig into the hill and sidecast below, to build it up to the desired size.
Excavation is carried back to the side of the ramp and to the south and west digging lines, in
any convenient manner, while the bulldozer shapes the bottom level, making a flat space as before.
When the front shovel starts work at the bottom (Fig. 4.30), the excavation and ramp removal
are carried out in the manner described earlier.

FIGURE 4.29 First cut in a downslope.