DRAINAGE METHODS FOR COUNTY ROADS. 47 
be provided by means of a concrete foundation, and under extreme 
conditions of this sort concrete is practically the only satisfactory 
foundation material. (Fig. 17.) 
DESIGN AND CONSTRUCTION. 
No matter what tj'pe of foundation may be selected for a particular 
road or section of road it should, of course, be designed and con- 
structed with a view to meeting adequately the conditions involved. 
Since these conditions vary greath T , sometimes even on the same proj- 
ect, it is manifestly impracticable to standardize either the design or 
construction of foundations except to a very limited extent. In the 
following discussion, therefore, no attempt will be made to do more 
than point out the limits of good design for each type of foundation 
and to describe, in a general way, what are believed to be the best 
methods of construction. Thus, unavoidably, much must be left to 
the judgment of those who design and superintend such work. 
Practical experience and observation disclose that the best roads 
usually have a great variety of foundations. These may have been 
1 6 'h t r'h 
5" to 8" 
CONCRETE FOUNDATION 
Fig. 17. 
laid at the time of original construction, or added to meet conditions 
that arise from season to season. For long distances the changes 
often occur as frequently as every few hundred feet. Rarely are con- 
structed foundations now laid mile after mile, as was done formerly 
on the pikes of central Kentucky and elsewhere. The cost of such 
work is so great that the individual and local treatment has more 
generally been adopted b}" highway engineers. 
GRADING AND PREPARING THE SUBGRADE. 
The discussion on bearing power of different soils should be con- 
sidered in connection with what is said here regarding the proper 
method of grading a road and preparing the subgrade. The table of 
bearing powers given on page 41 is based on the assumption that the 
roadbed and subgrade will be prepared in accordance with some such 
methods as those described below. 
The shape of the subgrade varies somewhat with different types 
of foundations or road crusts, but this feature does not need to be 
especially considered here, because the recommended shape for the 
subgrade is shown for each type of foundation discussed. Where 
