GENERAL DRAINAGE INFORMATION 71 



the country. They are sometimes used in conjunction 

 with tile drains, in heavy soils, and especially where the 

 topography is such as to bring the surface drainage into 

 depressions over or adjacent to main tile drains. 



103. Tile drainage. On most upland soils, except 

 in extended flat areas and in occasional cases of impervious 

 soils, tile drainage may be employed and is to be much 

 preferred. 



TILE 



104. Kinds of tile. Two general kinds of tile are 

 found on the market : (1) The common porous clay tile 

 and (2) vitrified tile. Vitrified tile, when glazed, as it 

 is sometimes, is often designated as a third kind. Drain 

 tiles are made in lengths of 12 inches and in diameters 

 ranging from 2 inches to 15 inches or more. Tiles less 

 than 3 inches in diameter are seldom used in modern 

 drainage practice. Any saving in cost that may come 

 from using 2-inch tile is more than counterbalanced by its 

 lack in efficiency as compared with 3-inch tile. 



105. Common clay tile. The ordinary clay tile is 

 made of the same material and in much the same way 

 that clay brick are made, and, after burning, possesses 

 much the same texture as the brick made of the same clay. 

 When made of good quality of clay and properly burned, 

 the tile is very durable, and after sixty to seventy years 

 in the soil, if it has been placed below the frost line, shows 

 no evidences of deterioration. If, however, the tile is 

 placed above the frost line, the walls are likely to shale, 

 and in a very short time to collapse. 



106. Vitrified tile. Vitrified tile differs from common 

 tile in two respects: (1) The kind and quality of the 

 material and (2) the degree of heat to which it is sub- 



