66 HIGHWAY CONSTRUCTION 



The pebbles in a gravel road are simply imbedded in a paste 

 and can be easily displaced. It is for this reason, among others, 

 that such roads are subject to internal destruction. 



The binding power of clay depends in a large measure upon 

 the state of the weather. During rainy periods a gravel road be- 

 comes soft and muddy, while in very dry weather the clay will con- 

 tract and crack, thus releasing the pebbles, and giving a loose 

 surface. The most favorable conditions are obtained in moderately 

 damp or dry weather, during which a gravel road offers several 

 advantages for light traffic, the character of the drainage, etc., 

 largely determining durability, cost, maintenance, etc. 



Repair. Gravel roads constructed as above described will 

 need but little repairs for some years, but daily attention is required 

 to make these. A garden rake should be kept at hand to draw 

 any loose gravel into the wheel tracks, and for filling any depres- 

 sions that may occur. 



In making repairs, it is best to apply a small quantity of gravel 

 at a time, unless it is a spot which has actually cut through. Two 

 inches of gravel at once is more profitable than a larger amount. 

 Where a thick coating is applied at once it does not all pack, and if, 

 after the surface is solid, a cut be made, loose gravel will be found; 

 this holds water and makes the road heave and become spouty 

 under the action of frost. It will cost no more to apply six inches 

 of gravel at three different times than to do it at once. 



At every one-eighth of a mile a few cubic yards of gravel 

 should be stored to be used in filling depressions and ruts as fast as 

 they appear, and there should be at least one laborer to every five 

 miles of road. 



Broken Stone Roads. Broken stone roads are formed by pla- 

 cing small angular fragments of stone on the surface of the earth 

 roadbed and compacting into a solid mass by rolling. This class 

 of road covering is generally called a Macadam or Telford road 

 from the name of the two men who first introduced this type into 

 England. 



The name of Telford is associated with a rough stone founda- 

 tion, which he did not always use, but which closely resembled that 

 which had been previously used in France. Macadam disregarded 



