2o6 



ENGINEERING ON THE FARM 



inches in depth. It should contain sufficient clay or bind- 

 ing material to cause it to pack and become hard. For 

 country roads the packing is usually done by the traffic. 

 More satisfactory results are obtained when the gravel 



*> 



14 



_^k ^ ^4 " s— G rave/ 



a-o 





y 



Fig. 181. Cross section of a gravel-clay road, built on very sandy soil. 



This road gave excellent satisfaction. 



is spread in several layers, sufficient intervals being 

 allowed between the placing of the layers to enable the 

 last one placed to become packed and solid before another 

 is put on. A first-class gravel road is made by a careful 

 selection of the materials, spreading in layers, sprinkling, 

 and rolling, the road being finished and ready for use in a 

 comparatively short time. Where the original roadbed is 

 composed of fine sand, a layer of clay should be spread over 

 the sand before the first coat of gravel is spread. 



Macadam. A macadam road (Fig. 182) is one in which 

 the covering is made of broken stone. Coarse large stones 



-/ "per fr Crown % "per ft. 



Fig. 182. Cross section of a macadam road 



are placed as a base and thoroughly rolled down. A layer 

 of small stone or good gravel is then placed on the base and 

 rolled. The depth of the covering and the size of the 

 materials used vary greatly according to the location and 

 traffic expected and the nature of the materials. 



Telford. A telford road (Fig. 183) is one made by the 

 method of laying a pavement of rough stone over a prepared 



