Page 136 - Moving the Earth_ The Workbook of Excavation

ROCK, SOIL, AND MUD

3.30 THE WORK

FIGURE 3.21 Compartment digging.

Compartments. Shallow bottom water may be largely kept out of the bucket by compartment digging,
as illustrated in Fig. 3.21. A ridge of clayey soil is left between the digging and the water until bottom grade
is reached. The ridge is then dug out and water allowed to flow in. Some mud will be washed onto the
digging surface by inflowing water and by the removal of the ridge. Compartments may be large or small.
This method gives waterfree digging for the bulk of the excavation, and can be used, with dimin-
ishing efficiency, in increasing depths of water, but not when the whole digging area is under
water, as in deepening an undrained pond.
If little surface water is present but groundwater drains into the excavation rapidly enough to be
a nuisance, digging can be in two or more compartments. First, the whole area is dug in layers until
it gets sloppy, after which the digging is concentrated in one spot until most of the water flows into
the hole made. An adjoining area, separated by a ridge, is then dug deeper and the ridge cut.
The water will now flow into the deeper hole, leaving the first one nearly dry and ready to be deepened
in its turn. This alternation of digging spots can be continued to the bottom of the cut. If the area is too
large to be dug in this manner, the water can be concentrated in gouges dug behind the regular layer cut.
Spoil. If enough dry or stiff dirt can be dug to build a dike along the excavation edge of the pro-
posed spoil pile, as in Fig. 3.22, it will prevent mud behind it from flowing into the hole. There is

FIGURE 3.22 Dike method of piling mud.