EARTH;, SAND-CLAY, AND GEAVEL ROADS. 



43 



content of the clay and the compactness of the roadbed. It should 

 be borne in mind that, in this case, it is better to have a surplus of 

 sand than a surplus of clay in the surface, because the former is more 

 easily corrected. 



Case 3. — Figure 21 illustrates the two principal steps involved -in 

 constructing a sand-clay surface with topsoil or other natural sand- 

 clay mixture. The roadbed should be graded in the usual way, ex- 

 cept that the portion to be surfaced should be trenched out with the 

 grading machine to receive the surfacing material. The surfacing 

 material should be spread to such a depth that it will be at least 8 



Flat or slightly crowned-} 



Cross section ready to receive the surfacing material 



Sec text for this depth 



4, r- see iexr toi in 



Cross section showing material spread on the road 

 ready for mixing 



I ,-8 to 10 inches 



'?,:■<>■/.;./■;■ ■- ■ - ~- ■-">'. "■■(:■ _^_ 



Cross section of completed road 



TYPICAL CROSS SECTIONS SHOWING METHOD OF CONSTRUCTING 

 SAND-CLAY ROAD BY MIXING SAND OR CLAY WITH THE ROAD BED MATERIAL. 



"W'should be at least 12 feet for single track road, and "S'generally not less than 

 5feet, for double track "W'should be not less than I4feet. and"S"not less than 3feet. 



"H?crown. varies from A" to the foot for level grade, to I" to the foot for a grade 

 of5%. 



Fig. 20. 



inches thick at the center when compacted. After this is done per- 

 mit traffic upon the road and keep the surface in shape with a road 

 drag while it is being compacted. Where surfacing material may be 

 obtained cheaply trenching is frequently omitted altogether, and the 

 artificial surface is extended out over the shoulders. 



Case 4- — Where it is. necessary to bring the sand and clay on the 

 road separately and mix them in place, the method employed should 

 be a combination of the methods already described. That is, a 

 trench should be formed with the grading machine to receive the 

 bottom layer of material, which may be either the sand or the clay, 

 and the top layer should then be spread and the mixing done as 

 described in Case 1 or Case 2. The depths of the respective layers 

 should be such as to secure a completed surface at least 8 inches 

 thick, and the proportions should be fixed in the manner already 

 described in discussing the other cases. Where the roadbed material 



