Page 183 - Moving the Earth_ The Workbook of Excavation

BASEMENTS

BASEMENTS 4.23

up nearly to the top. Another layer of shotcrete is applied, and the excavation is extended for the
next lift depth until the full planned depth is reached.

Dozer. A bulldozer or front-end loader may be used to advantage to dress up the ramp, smooth
the pit floor, and be ready to push overloaded or weak trucks up the ramp.
A crawler loader is preferred, as it does better trimming and can help with loading in an emer-
gency. A big one is most useful, but also most in the way.
Trucks. Trucks with 6- to 8-yard capacity are well matched to this size shovel, but anything
from 6 to 14 yards can be used. Small ones can maneuver more easily and work well on certain
types of soft ground. Large ones cause less traffic congestion, and under favorable conditions will
move soil at lower cost. If the pit is wet or sandy, all-wheel-drive machines are preferable. Trucks
must be in good condition to carry capacity loads up the ramp.

First Cut. In making the ramp, the shovel has worked straight ahead. Upon reaching the floor
level of the first cut, it may continue to the back wall, or it may first make a side cut, as in Fig.
4.21(A), so that trucks can turn around in the pit. If it works straight through to the back wall, it
is then walked to the foot of the ramp again to take another slice toward the back, as in (B), as
double spotting of trucks is easier when working away from the ramp than toward it.
Once the pit floor is widened enough to allow trucks to turn, the digging may be extended in
any direction so long as the shovel may be easily reached by trucks. Sooner or later the bank to
the east of the ramp is dug away, and usually part of the ramp itself, leaving it wide enough for
one truck only.
Stumps. When stumps are encountered, the shovel should dig around them before tackling
them directly. The depth of this cut is such that they can be undermined enough that their own
weight will help to break them out. Roots can be cut easily at a distance of a few feet from the
trunk, and the stubs splintered back. Many operators will waste much time, strain their machines,
by direct attacks on stumps which would shortly fall out in the ordinary course of digging.
When the stump is loose, it should be knocked around with the bucket to loosen the dirt, then
placed in a truck. The tailboard should be folded down or removed, unless the stump is to be lift-
ed off. With skill and luck, the shovel operator may be able to balance the stump on the bucket,
then tip it off onto the truck. It may be picked up also by a chain. If it is too heavy for the shov-
el to lift, the dirt should be dug out of it by hand, and all possible wood removed from it by saw-
ing and chopping.

Barricades. As digging approaches the sidewalk, barricades must be erected to keep specta-
tors from climbing or falling into the pit, and from using any part of the sidewalk likely to cave
in. These barricades may be solid wood fences, or may be perforated so that sidewalk superinten-
dents may watch the work. The contractor may be able to build up local goodwill by encouraging
spectators.
Furnishing adequate windows or peep holes reduces the dangerous practice of spectators
standing in the truck driveways to watch the work.

Finishing First Cut. The floor grade of this first drop is approximate, and a foot up or a foot
down is not important as long as it is easily passable to trucks. However, the walls must be cut
to whatever finish the job calls for. A good operator can cut a straight wall and an almost-square
corner with the bucket, but hand finishing is neater and saves machine time.

Bottom Cut. When the first level is complete, ramp cutting is resumed until the bottom is
reached, as in Fig. 4.21(C). Trucks will drive down the upper section, turn on the upper level, and
back down to the shovel. It is not necessary that the ramp continue in the same direction, but this
is the most economical method where the pit is long enough. Any turn must be made very wide
for the convenience of the trucks.