Page 172 - Moving the Earth_ The Workbook of Excavation

BASEMENTS

4.12 THE WORK

FIGURE 4.12 Three-pile system.

basement is dug by the three-pile or open-front method, the procedure shown in Fig. 4.12 may be
followed. The first layer is not cut quite to the ends of the excavation, (A), and the ramps built in
reaching the bottom are inside the digging lines, (B). They are cut back to the steepest practicable
grades on the last pushes, and then one ramp, a foot or so wider than the machine, is cut into the
bank. All soil left inside the digging line is then removed by being picked up and carried or pushed
out the slot ramp.
The machine can carry a larger load up the ramp when moving forward than when reversing.
This is because it is nose-heavy when loaded, a condition which is made worse in backing up an
incline, both by the shift of the center of gravity toward the front and by the reaction from the driving
torque which pushes the front down. In ascending a grade forward, both of these forces tend to raise
the front and improve stability. These effects become more pronounced as the incline becomes
steeper.
Turning around in a small excavation may be difficult, or impossible, so that it is often better
to back out with a small load than to take the time to turn in order to carry a larger one.

Cutting Walls. So far as possible, the excavation should be finished with vertical walls. Long
ones may be cut neatly by digging parallel to the edge, but because of limited space, much finishing
must be done by working straight toward the digging line.
Until the line is reached, the bank digging procedures in Chaps. 10 and 16 may be followed.
A vertical face may be cut by allowing bank resistance to move the tractor back as the bucket
rises. This may be managed by slipping the clutch with mechanical drive, or slowing the engine