ROADS AND PAVEMENTS 397 



is not available, the clay may be improved by burning it, 

 and then spreading and rolling it well. Trees and vegetation 

 should not be permitted along the sides of a clay road as they 

 exclude the sun and keep the road damp and muddy. 



Gravel Roads. Natural roads may be improved by using 

 a surface of gravel. The gravel should be of hard material 

 capable of resisting abrasion, and in order that it may bind 

 well together, it should consist ot pebbles of various sizes 

 from 2 in. down to the size of a pea. The binding is effected by 

 fine dust which fills the voids that cannot be filled by the small 

 pebbles. The fine material may consist of sand, clay, or loam 

 to the amount of one-eighth to one-fourth of the bulk. 



The thickness of the gravel covering will depend on the 

 extent and weight of traffic. It ranges from 4 in. for very 

 light traffic to 12 in. for the heaviest traffic. The gravel is 

 spread on the prepared roadbed in layers 4 in. thick, and each 

 layer is compacted by a roller of suitable weight, a heavy roller 

 being used for small and a light roller for coarse or large gravel. 

 A small quantity of water should be sprinkled over the gravel 

 in advance of the rolling; and, when all the layers are com- 

 pacted, a small quantity of clay or loam may be spread over 

 the surface and rolled without water, after which the roadway 

 may be opened to the traffic. 



Oiled Roads. Sand, clay, and gravel roads may be much 

 improved by the appl cation of crude petroleum oil; that hav- 

 ing an asphaltic base is the best. The oiling lays the dust 

 and, to a certain extent, serves as a binding material, forming 

 a crust that wears well under traffic. The oil is applied by 

 sprinkling while the road is dry, being mixed with the earth 

 or gravel by harrowing and then compacted by rolling. Two 

 applications are made. For the first one from about i to 

 1J gal. per sq. yd. is required. The second application of 

 about | gal. per sq. yd. is made a few months after the first one. 



Broken-Stone Roads. A broken-stone road consists of a layer 

 of broken rock spread on the previously prepared natural soil, 

 and consolidated to a firm uniform surface by rolling with steam 

 rollers. To secure satisfactory results, certain essential points 

 must be observed. The stone must be of suitable quality, 

 and must be placed on a suitable roadbed. The bed must be 



