EAKTH, SAND-CLAY, AND GBAVEL EOADS. 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 1\ 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 \\ 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 

 be 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 



