162 



AGRICULTURAL ENGINEERING 



The Construction of Stone Roads. As usually con- 

 structed, the stone surfacing in a country road is made from 

 12 to 15 feet wide. The stone proper is usually applied in 

 two layers, on top of which a third layer of stone dust or 

 other binding material is used. The lower course is usually 

 made from 2}4 to 4 inches thick, and the upper courses 

 from 13/2 to 2 inches thick. Thus the total thickness of the 

 stone varies from 4 inches to 6 inches at the center of the 



road, and from 2}^ inches 

 to 4 inches at the outer 

 edge. It is customary 

 to apply more material 

 in the center of the road, 

 where the wear from 

 traffic is the greatest, 

 than at the outside. 



If automatic dump 

 wagons are not used to 

 spread the stone, it is 

 generally recommended 

 that it be applied with 



Fig. 85. Model of a water-bound macad- shovels. When Stone is 



am road. A represents the prepared sub- -, -t • i +V>^ 



grade. B represents the first course of QUmpeCl in UeapS, tne 



coarse stone. C represents the second i o ^^ j tv-vI! +r\ 



course of stone, and D the finishing layer larger iragmeniS TOll lO 



of stone, chips or dust. (Bui. 36, Office of + i nil+c; irlp of thp nilp 



Public Roads, U. S. Dept. of Agr.) ^ ne OUlblUe OI iue pile 



and the finer portion is 

 left in the center. The stone should be applied in layers of 

 uniform thickness, making proper allowance for the shrink- 

 age due to rolling. The packing is done with a steam roller. 

 Horse rollers are not made heavy enough for this purpose; 

 the ten-ton traction roller is the size in general use. It is 

 customary to begin the rolling at the outside and work 

 toward the center. After the lower course is thoroughly 



