IIKIHWAY CONSTRUCTION 



The drainage of these soils may be effected by transverse drains 

 and deep side ditches of ample widt.li. The transverse drains are 

 placed across the road, not at right angles but in the form of an 

 inverted V with the point directed up hill; the depth at the angle 

 point should not be less than IS inches below the subgrade surface, 

 and each branch should descend from the apex to the side ditches 

 with a tall of not less than 1 inch in 5 feet. The distance apart of 

 these drains will depend upon the wetness of the soil; in the case of 

 very wet soil they should be at intervals of 15 feet, which may be 

 increased to 25 feet as the ground becomes drier and firmer. 



The transverse drains are best formed of unglazed circular tile 

 of a diameter not less than 3 inches, jointed with loose collars. The 

 tiles are made from terra cotta or burnt clay, tire porous, and are 

 superior to all other kinds of drains. They carry off the water with 

 greater ease, rarely if ever get choked up, and only require a slight 

 inclination to kee^ * t '* g water moving through them. 



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Fig. 10. Tile Drain. 



Fig. 11. Siltliasiii. 



The tiles are made in a variety of forms, as horseshoe, sole, 

 double sole, and round, the name being derived from the shape of 

 the cross-sections. Round tile is superior to all other forms. The 

 inside diameter of these tiles varies from 1} to inches, but they are 

 manufactured as large as 24 inches. Pieces of the larger pipe serve 

 as collars for the smaller ones. They are made in lengths of 12, 

 14 and 24 inches, and in thickness of shell from } of an inch to 1 inch. 



The collar which encircles the joint of the small tile allows a 

 large opening, and at the same time prevents sand and silt from 



