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 
Cross section ready to receive the surfacing material. 
4 to 7 inches 
Cross section showing the first course of gravel spread and rolled 
Broken line shows the finished road section. 
TYPICAL CROSS SECTIONS SHOWING METHOD OF CONSTRUCTING A GRAVEL ROAD 
"W" should be at least 10 feet for single track roadway and "S"generaJly 
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, 
be 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 
