Page 224 - Moving the Earth_ The Workbook of Excavation

DITCHING AND DEWATERING

5.26 THE WORK

Bell joints are resistant to chipping, will hold the pipe against slipping downhill, and, if the joints
are open, will reduce flow or seepage of water along the outside of the pipe; but they are difficult
to lay.
Slip joints are easier to handle and to lay because of the uniform outside diameter.
Pipes with greater than 12-inch inside diameter are usually reinforced, and this construction is
required on most jobs because of its additional strength.
Concrete may be attacked by water carrying certain alkali salts or other chemicals. It is subject to
erosion from fast-flowing water carrying abrasive material, and may scale or disintegrate slowly from
weathering. Structural difficulties may arise from the comparative weakness of its joints. However, under
a wide range of conditions, it is long-lived enough to be considered a permanent installation.

Ductile Iron Pipe. Some utility companies still use ductile iron pipe because of its inherent
strength, toughness, and versatility.

Tile. Tile may be porous or glazed, and is chiefly made in small and medium diameters, and in
1- to 4-foot lengths. The porous type usually has butt joints and is called land tile. Standard glazed
or vitrified tile has bell joints and is called sewer tile.
Tile is lighter than concrete and has excellent bearing strength and resistance to weathering and
corrosive chemicals. Its glazing resists erosion. It is fragile, and must be handled with care. In small
sizes it is cheap and easy to lay except on unstable ground.
Plastic Pipe. In small sizes, tile or concrete may be replaced by PVC (polyvinyl chloride) plastic
pipe. Standard pieces are 10 feet long, with butt ends that may be linked by sliding collars. Bottoms
may be solid to carry water, or perforated to take it in.
This pipe is light, easy to lay, and long-lasting. It is not brittle, and it is seldom broken in
handling.

Corrugated Metal. Corrugated pipe is made in standard, helical, and heavy-duty-constructions.
Cross section may be round, elliptical, flattened, or arched.
Standard pipe, illustrated in Fig. 5.18, is made up of galvanized plates of rust-resistant (but not rust-
proof) iron or steel, 16 gauge to 8 gauge, which are deformed with parallel corrugations or ripples.
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These are usually 2 ⁄ 3 inches from crest to crest and ⁄ 2 inch deep. They increase the strength of 16-
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gauge about 11 times, and of 8-gauge about 3 ⁄ 2 times.
The corrugated plates are rolled into cylinders slightly more than 2 feet long, which are lapped and
riveted together. Additional cylinders are lapped over the ends and riveted to obtain the desired length.
Inside diameters of standard riveted pipe range from 6 inches to 8 feet. Lengths may be made
up in any multiple of 2 feet, but transportation problems usually limit single pieces to 20 or 24
feet. Ends may be beveled or skewed.
Features of arched pipe are lower clearance, greater bottom capacity, and less tendency to settle
in soft ground.
Pipe sections are fastened together on the job by band collars. These may be one-piece or two-
piece. One-piece bands are usually fastened by compression bolts only. Two-piece may be riveted
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or bolted to the sections. Because of allowance for overlap, each pipe section is 1 ⁄ 2 inches longer
than its nominal length. Each joint adds the width of one corrugation.
Under normal conditions, corrugated pipe gives long service, but its life may be shortened by
chemicals or electrochemical action, and by erosion of the bottom.
Corrugated pipe is very much lighter than concrete or tile; it is not as readily damaged by care-
lessness or abuse; it is easily placed, connected, extended, or removed for salvage, and resists
movements of fill which would pull short-jointed pipes apart. Its internal flow resistance is higher
than that in other types. Its corrugations tend to keep it from moving in the fill, and discourage
seepage or overflow from following the outside. It will bridge low or weak spots in its supports.
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For subdrainage it can be drilled with ⁄ 16 - or ⁄ 8 -inch holes through the haunches.
Other Types. Oil or grease drums may have the ends cut out and the cylinders tack-welded together.
Such conduit is easy to handle, but compressive strength and resistance to corrosion are poor.