46 
BULLETIN" 124:, IT. S. DEPARTMENT OF AGRICULTURE. 
good quality of stone is available. Such foundations usually are 
well adapted for road crusts of gravel, macadam, bituminous con- 
crete, and, where the traffic is only moderate, for brick. (Fig. 15.) 
The V-drain foundation is adapted to locations where field stones 
are readily available and where drainage of the subgrade is an essen- 
tial function of the foundation. 
Stone base is a modification of Telford where quarry spalls and 
broken stone are used, as in V-drains, but where the subgrade is 
shaped as for Telford. Such stone should be laid on the subgrade so 
as to bear firmly and not rock, but need not be broken, coursed, and 
wedged so carefully as Telford. It is finished with fine material, 
CRUSHED STONE FOUNDATION 
Fig. 15. 
like gravel, small stone, or sand, and rolled. Its use is similar to that 
of Telford. 
Telford foundations have been used seldom except with macadam 
or gravel crusts. The reason for this is that the surface of a Telford 
foundation is irregular and such materials as gravel or crushed 
stone are well adapted to correcting the' irregularities. Such advan- 
tage as Telford has over crushed stone foundations lies in the fact 
that since the individual stones are placed by hand larger stones are 
used that have greater bearing areas and give better distribution of 
pressure on the subgrade. This is an important consideration where 
TELFORD FOUNDATION 
Fig. 16. 
the subgrade is not very stable and the necessary rolling of a crushed 
stone foundation might produce a wavy surface. (Fig. 16.) 
Concrete foundations are well adapted for use where the road crust 
consists of brick, asphalt, bituminous concrete, or any other material 
whose integrity and stability can be maintained only when extreme 
rigidit}^ is supplied by the foundation. In addition to their rigidity, 
concrete foundations, when properly constructed, present fewer un- 
certainties due to lack of uniformity in materials and workmanship 
than any other type, and on that account are greatly to be preferred 
where the road crust is of an expensive type. Insurance against fail- 
ure due to lack of uniformity in the subgrade can also, perhaps, best 
