EARTH, SAND-CLAY, AND GRAVEL ROADS. 



53 



is 8 inches at the center and 6 inches at the edges. The difference in 

 thickness between the edges and the center is effected by making the 

 crown of the subgrade flatter than that of the surface. 



The construction of a gravel road usually is divided into two 

 entirely distinct classes of work. The work of grading and prepar- 

 ing the subgrade falls into one class, and that of hauling, spreading, 

 and compacting the gravel into the other. The first class of work 

 has been discussed at considerable length in connection with earth 

 and sand-clay roads, but since it is desired to emphasize certain 

 features of subgrade preparation that are of increased importance 



6 to 10 inches 

 Cross section ready to receive the surfacing material. 



TYPICAL CROSS SECTIONS SHOWING METHOD OF CONSTRUCTING A GRAVEL ROAD 



"W'should be at least 10 feet for single track roadway and "S" generally 

 not less than 5 feet-, for double track, "W'should be not less "than 14 feet 

 and"S"not less than 3 feet 



"H" crown, varies from £ inch per foot for level grade, to' I inch per 

 foot for a grade of 5% . 



Fig. 22. 



in connection with gravel road construction, both classes of work will 

 be considered in the following discussion. 



PREPARATION OF THE SUBGRADE. 



In grading the roadbed and preparing the subgrade for a gravel 

 surface, all of the precautions previously noted as applying to similar 

 features of earth and sand-clay road construction should, of course, 

 he observed. It should be borne in mind also that the more expensive 

 a road surface, the greater should be the care exercised to prevent 

 it from being damaged through settlement or upheaval of the sub- 

 grade, and the greater should be the accuracy with which the sub- 

 grade is constructed, so that no unnecessary surfacing material may 

 be required to correct irregularities in grade and cross section. No 

 matter what the soil conditions may be, the subgrade for a gravel 

 road surface, when completed, should conform closely in grade and 

 cross section to the requirements of the plans and should present 



