DRAINAGE METHODS FOR COUNTY ROADS. 45 
local. Such sections as develop difficulties of this sort should be 
treated individually in order to get the best generally good results at 
lowest cost. 
FOUNDATION TYPES. 
The types of foundations in common use for country roads are 
(1) gravel, (2) crushed stone, (3) V-drains, constructed of field 
stones, (4) stone base, (5) Telford, and (6) Portland-cement con- 
crete. Selected earth, sand, and cinders also have been used fre- 
quently to improve the supporting power of subgrades, but since the 
addition of such materials makes no essential difference in the gen- 
eral method of preparing the subgracle. they will not be considered 
as foundation materials. Eoad foundations have been constructed 
of brick, boards, corduroy, and many other special materials, 
and such construction is no doubt sometimes justified, although it is 
usually of a makeshift nature. In these cases the problem generally 
is concerned with employing local materials which may be secured 
at small cost and is one to be solved on the ground or after all the 
affecting conditions have been considered. 
GRAVEL FOUNDATION 
Fig. 14. 
From what has been said it is evident that no very exact rules can 
be stated for determining what, if any, type of foundation should be 
selected as best for a general case. Foundation troubles are com- 
monly local and peculiar and yield most readily to special treatment. 
The considerations that should influence the judgment in making a 
selection for a particular case are efficiency, and availability of mate- 
rials, and cost of construction. It is possible to design foundations 
of any type mentioned above which would be efficient for any given 
condition of subgrade and type of road crust, but considerations of 
economy usually will serve to reduce the number of practicable types, 
for any particular case, to not more than two or three at most. 
In general, gravel foundations are adapted to cases where the road 
crust also is to be of gravel or some other simple type, or where only 
slight additional stability is required for the subgrade to support 
concentrated loads on the road surface without being deformed. 
But, if the gravel possesses high cementing value, it may be used 
satisfactorily for foundations where crushed stone or concrete other- 
wise would be required. (Fig. 14.) 
Crushed-stone foundations have been used for practically all types 
of road crusts where the subgrade conditions are favorable and a 
