The above figure represents the horse-shoe tiles and soles properly placed.
As this form of tile has been generally used by the most successful drainers in New York, it may be well to cite the high authority of Mr. Gisborne for the objections which have been suggested. It should be recollected in this connection, that the drainage in this country has been what in England would be called shallow, and that it is too recent to have borne the test of time.
Mr. Gisborne says:
"We shall shock and surprise many of our readers, when we state confidently that, in average soils, and still more in those which are inclined to be tender, horse-shoe tiles form the weakest and most failing conduit which has ever been used for a deep drain. It is so, however; and a little thought, even if we had no experience, will tell us that it must be so.
"A horse-shoe tile, which may be a tolerably secure conduit in a drain of 2 feet, in one of 4 feet becomes an almost certain failure. As to the longitudinal fracture, not only is the tile subject to be broken by one of those slips which are so troublesome in deep draining, and to which the lightly-filled material, even when the drain is completed, offers an imperfect resistance, but the constant pressure together of the sides, even when it does not produce a fracture of the soil, catches hold of the feet of the tile, and breaks it through the crown. When the Regent's Park was first drained, large conduits were in fashion, and they were made circular by placing one horse-shoe tile upon another. It would be difficult to invent a weaker conduit. On re-drainage, innumerable instances were found in which the upper tile was broken through the crown and had dropped into the lower."
Another form of tiles, called sole-tiles, or sole-pipes, is much used in America, more indeed than any other, except perhaps the horse-shoe tile; probably, because the first manufacturers fancied them the best, and offered no others in the market.
In this form, the sole is solid with the tile. The bottom is flat, but the bore is round, or oval, or egg-shaped, with the small end of the orifice downward.
Fig. 31—Sole-Tile.