36 



BULLETIN 724, U. S. DEPARTMENT OF AGEICULTUEE. 



proper position and* to prevent displacement of the pieces of tile 

 used for covering the joints. The back filling then may be com- 

 pleted, when convenient, with plows and drag scrapers, and after 

 the surface over the drain has finished settling, it may be smoothed 

 to the required shape with a road grader or- a split-log drag. 



If the drains are laid in the center of the road the back fill should 

 be rammed carefully and firmly just as soon as enough has been 

 placed to protect the pipe from displacement and damage. The back 

 filling then should continue in layers, each one being rammed to pro- 

 vide so far as possible against settlement. 



Where tile drains are constructed through unusually retentive soil 

 and it is desired to secure the maximum efficiency from them, the 

 trench should be back filled with crushed stone or gravel for 6 or 8 

 inches around and above the pipe. The proper method of making a 

 back fill of this kind is indicated in the typical specification on 

 page 81. 



HEAD WALL FOR DRAIN TILE 



Concrete, 1:2:4 mixture 





1 



SI 







4 



L 



— > 



-i 



c 



^" rods = Galvanized 



h about 12" corresponding'L" 5-0' 



Fig. 12. 



TILE-DRAIN OUTLETS. 



Figure 12 show^s an outlet for a tile drain protected by means of a 

 head wall. The head wall prevents the end of the drain from being 

 undermined and- destroyed and also holds the earth in place at that 

 point. The swinging screen over the end of the tile, which is shown 

 in the figure, is intended to prevent rodents and other small animals 

 from obstructing the tile with nests during dry seasons. In the past, 

 outlets have not always been protected in this Avay and as a result 

 trouble has been experienced frequently. 



Satisfactory head walls may be constructed of stone, brick, or 

 concrete. Wooden boards also have been used for this purpose, but 

 are subject to the disadvantage that they must be replaced- every few 

 years, while the other materials are practically permanent. The 

 screen over the end of the tile may be made of steel rods sharpened 

 at their lower ends, and is suspended from the head wall by means 

 of staples and links. 



