34 



HIGHWAY CONSTRUCTION 



entering the drain. Perishable material should not be used for 

 jointing. When laid in the ditch they should be held in place by 

 small stones. Connections should be made by proper Y-branches. 

 The outlets may be formed by building a dwarf wall of brick or 

 stone, whichever is the cheapest or most convenient in the locality. 

 The outlet should be covered with an iron grating to prevent vermin 

 entering the drain pipes, building nests and thus choking up the 

 waterway. (See Fig. 12.) 



Fig. 12. Outlet. 



Silt-basins should be constructed at all junctions and wherever 

 else they may be considered necessary; they may be made from a 

 single 6-inch pipe (Fig. 11) or constructed of brick masonry. 



The trenches for the tile should be excavated at least 3 feet 

 wide on top and 12 inches on the bottom.. After the tiles are laid 

 the trenches must be filled to subgrade level with round field or 

 cobble stones; stones with angular edges are unsuitable for this 

 purpose. Fine gravel, sand, or soil should not be placed over the 

 drains. Bricks and flat stones may be substituted for the tiles, 

 and the trenches filled as above stated. 



As tile drains are more liable to injury from frost than those 

 of either brick or stone, their ends at the side ditches should not 

 in very cold climates be exposed directly to the weather, but may 

 terminate in blind drains, or a few lengths of vitrified clay pipe 

 reaching under the road a distance of about 3 to 4 feet from the 

 inner slope of the ditch. 



.Another method of draining the roadbed offering security from 

 frost is by one or more rows of longitudinal drains. These drains 

 are placed at equal distances from the side ditches and from each., 

 other, and discharge into cross drains placed from 250 to 300 feet 



