Page 250 - Moving the Earth_ The Workbook of Excavation

DITCHING AND DEWATERING

5.52 THE WORK

As the ditcher moves forward, the blade smooths and shapes the bottom of the ditch. The front
hopper spreads a strip of gravel on the bottom. The thickness of this strip is regulated by raising
or lowering the hopper spout. The tile is laid on the gravel, with the ends touching. The tar paper
rolls off its spool to cover the pipe, and the rear hopper deposits gravel on it.
The bottom of the rear plate may be curved to smooth over the top of the gravel, or may be set
to ride several inches above it. A dozer works immediately behind the machine, backfilling. This
is necessary, for if the ditch is allowed to stand open an appreciable time, one of the walls might
move horizontally and slide the tile out of line.
The gravel may be piled beside the digging line, outside of the tile string, and placed in the
hoppers by a small tractor front loader. A hydraulic control clamshell bucket is more efficient than
the regular loader bucket, as it picks up the gravel without pushing it around.
A tile box is best adapted to a wheel ditcher, as it does not disturb its digging balance. Operation
on a ladder ditcher is possible, but is more difficult as it tends to pull the bottom of the ladder back-
ward and upward.
Backfilling. In agricultural work, it is customary to backfill with the soil dug from the ditch
after placing the pipe and whatever porous material is required. However, if it is to act as an inter-
cepting or curtain drain, imported porous material—such as gravel, sand, or corncobs—may be
used to near plow depth. A top layer of native soil should be used to prevent surface water from
washing it with its probable burden of silt and trash.
Whatever type of material is used next to the tile, it may be advisable to place it carefully by
hand until there is no danger of the pipe sections rolling out of alignment. Compacting it imme-
diately over the pipe (blinding) may reduce silting.
Gradients (Fall or Slope). Figure 5.42 indicates graphically the most desirable gradients for
land tile of various sizes. It will be noted that up to 6-inch diameter a minimum of 1 percent is
desirable, over 2 percent is optimal, and that larger sizes require flatter slopes.
Steeper slopes may give sufficient velocity to create eddies that will erode material below the
joint, with possible undermining of the tile. This may result in stoppage, in blowing out to the surface,
or in washing out of sections of line.
When steeper overall slopes are required by the topography, tiling may be done in a series of
benches or levels, connected by inclines of sewer tile with cemented joints.

FIGURE 5.42 Tile slope chart.