ROADS 



157 



as surface construction. In this method the gravel is hauled 

 and dumped on the prepared road bed, which usually is an 

 earth road, and the packing is left to the traffic. Sometimes 

 little attention is given to the matter of smoothing and 

 spreading the gravel. 



The thickness of surface gravel applied in this manner 

 varies from 3 to 6 inches at the center, usually tapering down 

 to a less thickness at the sides. It is considered the best 

 practice to apply the gravel in two layers; thus if the total 

 thickness of six inches of gravel is to be applied, it will be 

 spread in two layers 



three inches each. After 

 the first has been spread, 

 sufficient time should be 

 allowed for the traffic 

 to pack it quite thor- 

 oughly before the second 

 layer is spread. 



Trench Method. In 

 the trench method the 

 road surface is carefully 

 graded and rolled to re- 

 ceive the gravel. Usually 

 banks are provided at 

 the side which will hold 

 the gravel on the road 



Fig. 



83. Model of a gravel road illus- 

 trating the trench method of construction. 

 A shows prepared sub-grade; B, first course 

 of gravel; C, upper course of gravel. (Bui. 

 36, Office of Public Roads, U. S. Dept. of 



proper. In trench con- Asr) 

 struction the gravel is usually placed in two or more layers, 

 the first being composed of coarse pebbles, and is thor- 

 oughly rolled with a heavy roller before the other courses 

 are applied. This form of construction gives a finished 

 road at once, and for this reason is more desirable than the 

 surface method. This is much more expensive, however. 



