BRICK ROADS. 



11 



fact that more brick pavements have failed on account of defective 

 foundations than from any other cause should never be lost sight of 

 by those planning and supervising this class of work. Plate I 

 shows typical illustrations of what is likely to occur whenever this 

 feature of the work is neglected. Both of the roads here illustrated 

 were comparatively new, but failed when subjected to heavy motor- 

 truck traffic. The one shown in Plate I, figure 1, had a rolled gravel 

 foundation constructed under inadequate specifications and poor in- 

 spection, while in the other case a 4-inch concrete foundation was 

 specified, but an inspection made after failure revealed that the con- 

 crete was of an inferior quality and that its thickness was generally 

 less than that required by the specifications. 



The proper type of foundation or base depends largely on the 

 material composing the subgrade and the character of traffic for 



Fig. 2. — Concrete curb and gutter combined. 



OPRRE 8994 



which the road is designed. Where the traffic is comparatively light 

 and the subgrade is composed of some firm material which does not 

 readily absorb water, a very satisfactory base may be constructed of 

 broken stone. Where the traffic is comparatively heavy or where the 

 material composing the subgrade is at all unstable, a monolithic con- 

 crete base should be used. Bases consisting of a course of brick laid 

 flat upon a previously compacted layer of gravel or broken stone have 

 sometimes been used, and pavements constructed upon bases of this 

 kind, ordinarily called " double-layer " pavements, have in general 

 proved satisfactory. At the present time, however, such bases can 

 rarely be constructed at less cost than the more durable concrete bases, 

 ancl they will therefore be given no further consideration here. 



Broken-stone bases should be from 6 to 8 inches thick after com- 

 pacting and should be constructed in two or more courses just as in 



