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 qualit}^ 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 8094 
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 satisfactor} 7 . At the present time, however, such bases can 
rarely be constructed at less cost than the more durable concrete bases, 
and 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 
