Page 187 - Moving the Earth_ The Workbook of Excavation

BASEMENTS

BASEMENTS 4.27

BACKHOE EXCAVATION

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This basement might also be dug entirely by one full-revolving hydraulic backhoe, bucket size 1 ⁄ 2
yards or larger. Such a machine may take an 18-foot depth in one layer, and cut foot wall trenches also.
If ground conditions permit, trucks are loaded on the pit floor, for maximum output (Fig. 4.23).
The hoe would cut the ramp first, backing away from the street.
This 90-foot width is best taken in three strips, the first from front to back, the others from back
to front. Walls are trimmed and trenches cut as parts of the main digging.
The final step is to move around onto the ramp, then dig it, backing up.

FIGURE 4.23 Full-depth excavation with a hoe.

GROUNDWATER

The most common difficulty is groundwater. It may be in the form of springs or underground
streams, or a nearly stagnant water table with capillary water moistening the soil for several feet
above it. Wet soils usually turn to mud when loaded or disturbed and impede or bog down trucks.
If the first level should have a firm floor, but water be encountered in the next layer, trucks
would not be able to operate on the bottom without expensive aids, so that removal of this bottom
layer with a dipper stick would be impractical. The backhoe would not be bothered unless there
were sufficient water to hide the bottom, in which case it would have to be pumped out. Special
dangers connected with such pumping will be discussed below.
Information about underground conditions may be obtained from test borings or pits on the
site; from people who have dug basements or ditches in the neighborhood; and from geologists.
Such data may predict with reasonable accuracy the depth at which mud, water, loose sand, or
rock might be expected, and digging plans can be made accordingly.