Page 247 - Moving the Earth_ The Workbook of Excavation

DITCHING AND DEWATERING

DITCHING AND DEWATERING 5.49

TILE DRAINS

The simplest type of drainage by underground tiling is shown in Fig. 5.39 (A). A trench is exca-
vated, the bottom smoothed to the desired gradient; butt joint land tile may be laid with ends
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touching, or with spaces up to ⁄ 4 inch; and the trench is backfilled.
Water from the affected area drains into the tile through the joints and flows inside the tile to
the outlet. Under favorable conditions, such a drain may function for a very long time. However,
dirt falling in through the joint and entering with the water may fill it up, or plug low spots left by
subsidence of the ditch bottom.
In (B) the tile is laid on a bed of gravel. This provides a firmer foundation and a porous space
into which dirt can drop through joints from the pipe. This storage space for silt may fill so that
the pipe will ultimately fill also; but it may serve to trap all dirt brought in during a period of
adjustment, after which little or no dirt will move.
In (C) the pipe is surrounded by gravel, which preferably should be a mixture of pieces rang-
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ing from coarse sand to ⁄ 2 -inch crushed stone. This serves to filter dirt out of incoming water,
keeps loose dirt from reaching the pipe joints, and provides a good bedding.
Tar paper or hay can be used in connection with any of these techniques. It can be laid over
the pipe, where it prevents dirt from falling in, particularly when a large opening has been caused
by misalignment. The joints may be wrapped individually, or covered by a continuous strip.

FIGURE 5.39 Tile drains.