Page 223 - Moving the Earth_ The Workbook of Excavation

DITCHING AND DEWATERING

DITCHING AND DEWATERING 5.25

Dredging of small streams is generally done from the banks by draglines or clamshells, and of large
ones by floating dredges. The material dug may be piled on the banks, or removed by trucks or barges.
When the spoil is used to build banks to control stream direction, it must be protected by paving,
masonry, rock, logs, wired brush, sod, or other material. The best emergency protection for a bank
that is being washed away is drilled boulders fastened together in groups of three with steel cable.
River dredging may be planned to direct the river current so that it will do most of the exca-
vating in the new channel.
Drainage channels are often paved to protect them from erosion or slumping, to prevent chang-
ing of course, and to increase capacity by reducing friction.
Irrigation canal pavements may be used for any of these purposes and to prevent water from
leaking out of the canal into surrounding soil.
Check Dams. When the slope of a channel or gutter is so steep as to make erosion likely, it can
be divided into a series of easy gradients, and separated by check dams over which the water falls
steeply.
It is important that each dam have a center spillway large enough to prevent water from overtop-
ping the edges and eroding the earth alongside. An apron is also necessary to prevent undermining.
Where elaborate structures are not practical, crude ones made out of brush and logs or loose
stones may serve the purpose.

PIPE

Drain and culvert pipe is made in sizes with inside diameters ranging from 3 inches to 15 feet.
Materials include concrete, tile (vitrified clay), plastic or PVC, and corrugated iron or steel.
Figure 5.17 indicates the names of various parts of a pipe cross section. There are pipe design
books to use for selecting drainage pipes.
Ordinary vitrified clay pipe is comparable in strength to plain concrete sewer pipe, and fiber-
reinforced plastic to reinforced-concrete culvert pipe. The tile is brittle and fragile to handle.
Concrete. Concrete pipe may be plain or reinforced; the joints may be butt, bell, slip joint, or
gasketed. Size range is from 4 inches in inside diameter and up. Lengths are 2, 3, 4, and 8 feet.
Butt (open) joints are used for land tile.

FIGURE 5.17 Pipe details.