36 
BULLETIN 724, TJ. S. DEPARTMENT OF AGRICULTURE. 
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 
r\2h 
Concrete, 1:2:4 mixture 
c 
3 rods = Galvanized 
h about 12", corresponding'1" 5-0' 
Fig. 12. 
TILE-DRAIN OUTLETS. 
Figure 12 shows 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 way 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. 
