82 BULLETIN 724, U. S. DEPARTMENT OE AGRICULTURE. 
Where curves occur in the alignment the tile shall be laid accurately to the 
arc of the curve, and if straight sections are used the joints shall be covered 
with broken tile or cement mortar. 
As soon as the tile is laid as above provided and approved by the engineer, 
it shall be covered to a depth of about 6 inches with earth which contains no 
stones larger than 1 inch in diameter and which shall be thoroughly tamped as 
it is placed. The earth used for this purpose shall be moist when it is .placed 
over the tile and shall be of such quality that it will not run into the tile 
through the joints. The covering shall be very carefully done so as not to dis- 
turb the tile in any way. 
After the tile has been carefully covered as above provided, the entire trench 
shall be back filled. The material used for back filling shall be thoroughly 
tamped as it is deposited in the trench, and if the engineer so requires, the 
material of the back fill shall be heaped above the proposed surface over 
the trench so as to allow for subsequent settlement. 
OUTLET. 
Tile drain outlets shall be protected with head walls as shown on the plans, 
and shall be covered with suitable gratings of iron or steel. The upstream end 
of the drain shall be filled with stone, concrete, or some other durable material 
which will prevent earth from entering the drain at this point. 
ALTERNATE SPECIFICATION FOR BACK FILLING THE TRENCH AROUND AND OVER A 
DRAIN THROUGH STIFF CLAY. 
Before the tile is laid the bottom of the trench shall be covered with a 2-inch 
layer of gravel or crushed stone of such size that all would pass through a 
li-inch- mesh screen and be retained on a one-half inch mesh -screen. 
(Insert specification for laying tile.) 
After the tile is laid as above specified it shall be covered to a depth of 1 
foot with gravel or crushed stone of the kind specified for the bottom layer. 
This covering shall be thoroughly tamped over and around the tile, but in 
such a manner as not to disturb the tile in any way. The trench shall then be 
filled to the required depth with gravel or crushed stone of the size elsewhere 
defined in these specifications for " No. 1 stone," and the entire back fill shall be 
thoroughly tamped as it is deposited in the trench. The work of making the 
back fill shall be so carried on as to prevent sand, silt, earth, or other foreign 
material from getting into either the drain or -the interstices of the back fill, 
and in case this requirement is not observed the contractor may be required 
to rebuild the drain entirely at his own expense. 
GRADING. 
Grading shall include the moving of all earth, stone, and any other material 
that may be encountered, all filling, borrowing, trimming, picking down, 
shaping, sloping, and* all other work that may be necessary to bring the road 
and subgrade to the required grade, alignment, and, cross section, the clearing 
out of waterways and old culverts, the excavation of all necessary drainage 
and outlet ditches, the grading of a proper connection with all intersecting 
highways, the grubbing up and clearing away of all trees, stumps, and bowlders 
within the lines of the improvement, and the removal of any muck, soft clay, 
or spongy material which will not compact under the roller, so as to make a 
firm, unyielding subgrade. 
