Page 188 - Moving the Earth_ The Workbook of Excavation

BASEMENTS

4.28 THE WORK

Special conditions might require taking out the ground in three levels, or in one. The pattern
should be such that the maximum amount of dirt would be dug by front shovel, on levels which
permit trucking. When thin cuts are made, the front shovel can load trucks standing on the upper
level, but the extra dumping height slows the digging, and in some materials the bank would not
be stable enough to support trucks.

Drainage. Mud can be dried by draining or pumping the water. If the stormwater drain in the
street is sufficiently low, arrangements should be made to connect with it before excavating. A
ditch is dug from the pipeline in the street to a spot several feet inside the excavation area, and a
pipe with sealed joints laid, opening into the storm drain. At the basement end, a vertical pipe of
tile or concrete sections with unmortared joints or a perforated pipe is erected, as in Fig. 4.24(A)
and (B). Sand or clean gravel is placed around the vertical pipe as the trench is backfilled, or a
wooden barrier is placed to prevent backfill from closing the hole around it.
Each level made during the digging should be sloped to drain to this pipe, which can be opened
at any level.
This installation will also serve to remove some groundwater from the site, before excavation.
A general lowering of the water table may be obtained by ditching on the three open sides, as
in (C), or ditching the center also, as in (D). The edge ditches make the digging easier, but the
interior trenches complicate it. Heavy wood mats are required wherever shovels or trucks cross
them, and these are expensive to build and a nuisance to handle.
If the stormwater drain is not low enough to be useful, similar ditches may be dug and con-
nected with a piped or open sump from which water can be pumped to a catch basin in the street.

FIGURE 4.24 Drainage for excavation.