EARTH, SAND-CLAY, AND GRAVEL ROADS. 67 
gravel is spread and shall be filled with No. 1 gravel to within 2 inches of the 
finished surface of the shoulder. 
The contract price for shoulder drains shall be compensation in full for 
constructing them as above specified, except that the No. 1 gravel used shall 
be paid for by the ton at the price bid for No. 1 gravel in place in the first 
course. 
Gravel surface. — On the subgrade, prepared as herein specified, shall be con- 
structed a gravel surface of the cross section and number of courses shown on 
the plans, and each course when compacted shall have the thickness indicated 
on the plans. 
Gravel. — The gravel used in this work shall consist of hard durable particles 
of stone mixed with sand and clay or other bonding material. Not less than 
55 per cent nor more than 75 per cent, by weight, of the gravel shall consist of 
stone particles sufficiently large to be retained on a one-fourth inch mesh screen. 
The material passing a one-fourth inch mesh screen shall consist of sand and 
clay or other bonding material which, when tested in the manner described 
in Department Bulletin No. 347, " Methods for the Determination of the 
Physical Properties of Road-building Rock" (p. 15), shall have a cementing 
value of not less than 50. This material shall not contain more than 33 per 
cent, by weight, of clay. The material retained on a one-fourth inch mesh 
screen shall be graded from fine to coarse so that not more than 75 per cent and 
not less than 25 per cent will pass a three-fourths inch mesh screen. 
The gravel for the first course, hereafter designated as " No. 1 gravel," shall 
not contain any particles which would be, retained on a screen having circular 
openings 2| inches in diameter. The gravel for the wearing course, hereafter 
designated as " No. 2 gravel," shall not contain any particles which would be 
retained on a screen having circular openings If inches in diameter. 
Gravel obtained from the pits located at [insert location descriptions of ap- 
proved gravel pits] will be acceptable under this specification, provided that, if 
necessary, the gravel shall be screened to remove any excess of either fine or 
coarse material which it may contain above the limits specified. 
First course. — The first course shall consist of a single layer of No. 1 gravel, 
spread uniformly to such a depth that when compacted it will have the thick- 
ness shown on the cross-section drawings. The gravel shall be spread by hand 
from dumping boards or by dump wagons of a type that will distribute the 
gravel evenly over that part of the subgrade to be covered by the load or by 
wagons that will distribute it uniformly over the subgrade in rows containing 
not more than 1,000 pounds of gravel in a length of 10 feet. In order to secure 
the required thickness for the course, the contractor shall, if required by the 
engineer, set wooden guide blocks upon the subgrade at frequent intervals. 
These blocks shall be about 6 inches square and of a height equal to the re- 
quired depth of the loose layer, and the gravel shall be spread flush with the 
tops of the blocks. After the gravel has been spread, as above specified, it 
shall be harrowed with a tooth harrow until the different-sized particles and 
the cementing material are evenly distributed through the mass. It shall then 
he rolled until it is thoroughly compacted and firm. The rolling shall begin at 
one edge of the course, one rear roller wheel overlapping the shoulder from 2 
to 6 inches, and shall progress gradually to the center of the road in such a 
manner as to insure the uniform compacting of the gravel. The rolling shall 
then begin at the opposite edge and proceed as above. All irregularities and 
depressions that may develop shall be corrected immediately by reharrowing 
and adding No. 1 gravel, and the rolling shall be repeated, so that when the 
course is completed it shall be well compacted and firm and shall conform to 
