Page 219 - Moving the Earth_ The Workbook of Excavation

DITCHING AND DEWATERING

DITCHING AND DEWATERING 5.21

remaining soil is pushed parallel with the ditch into the main pile as in (C), or, when the end is
reached, distributed along the ditch.
There will usually be too much soil because of the increase in volume of disturbed soil and
space occupied by the pipe laid. The excess may be mounded up over the trench and partly com-
pacted by use of a roller, or by driving the dozer or a truck along it. Full natural settlement may
take as much as a year, and is liable to leave low and high spots to be graded in.
If the trench is small, it may be refilled by running an angle dozer or a grader through the pile,
with the blade set to sidecast it into the ditch as in (D).
Heavy backfill may be done by a front shovel walking through the length of the pile, digging
it and dumping in the ditch. A backhoe or a dragline can work from across the ditch, pulling the
soil into it. A dragline’s efficiency will be greatly increased by fastening a heavy plank or other
block across the mouth of the bucket so that it will not fill. Shovels often are used to move the
bulk of the backfill, with a bulldozer doing the final cleanup.
When pavement along the sides of the ditch is to be preserved, the best tool is a rubber-tire loader
or dozer, but light or medium crawler machines, with semigrousers or flat shoes, may be used.
Special dragline-type backfillers are often used on cross-country trenches.
Compacted Backfill. If a pavement is to be laid over the refilled trench immediately, the backfill must
be carefully compacted from the bottom up. This may be done by dozing or hand-shoveling fill slowly,
while workers in the trench compact it with hand or pneumatic tampers. A mechanical tamper may work
from the side or straddle the trench. The top layer may be compacted by use of a trench roller with a large
wheel that will fit inside the ditch, or by running any heavy machine back and forth along it.
Open-textured soils may be effectively compacted by puddling. Enough water is added to the
fill to make it into mud, which, upon drying, will shrink considerably. Fine-grained soils take a
long time to dry, and thus are not as readily handled in this way.
Machinery should not be run along wet trench fills as it is almost sure to get stuck in them.

Imported Backfill. Drainage trenches may be filled with better-draining, more porous material.
Spoil removed in the original digging is trucked away or used in grading, and the gravel trucked in
for refilling. This may be dumped in piles in and alongside the ditch, and pushed into it by a dozer
or grader or hand-shoveled. If considerable work of this type is to be done, a backfilling machine
may be profitably used. This carries a hopper that is moved parallel with the ditch by rubber-tire
driving wheels. Trucks dump into the hopper, from which a belt carries the soil to the ditch and
dumps it. The backfiller can push the truck that is dumping into it, so that the truck driver can con-
centrate on lifting the body at proper speed.

DEWATERING

DRAINAGE

Both the surface and the subsurface water may be removed by a seasonal drop in groundwater
level; by drainage through ditches, pipes, or siphons; by pumping; by walling off or diverting the
sources of water; and very often by combinations of two or more of these methods.
The purpose of dewatering may be to promote growth of crops; to dry out swamps or other
objectionable wet areas that are not designated wetlands (see Chap. 6); to stabilize slopes, foun-
dations, and road subgrades; or to facilitate excavation for any purpose.
All of these objectives except the last are accomplished chiefly by drainage—that is, causing
the unwanted water to flow away through artificial and natural channels or conduits. Pumps may
be used to remove water from a sump or low point of a drainage system.