44 BULLETIN Tli, U. S. DEPAETMENT OF AGRICULTURE. 



especially true of maciidam and, as a consequence, both V-clrain and 

 Telford foundations have been employed frequently in connection 

 "with the macadam surface. It is less true of Portland-cement con- 

 crete only because its power of distributing pressure increases very 

 rapidly with the depth and also ma}^ be greatly increased by prop- 

 erly arranged steel reinforcement which is usually cheaper to employ 

 than any form of foundation. 



Other types of road crust, such as blocks or setts, asphalt, and bitu- 

 minous concrete, are intended only as wearing surfaces and in gen- 

 eral must be supported on some form of artificial foundation. There 

 are, of course, exceptional subgrade conditions where this is not true, 

 as, for example, in the peninsular section of Florida, where the cli- 

 mate is mild and the soil consists essentially of sand which, when 

 properly confined, has a relatively high bearing power under all 

 weather conditions to which it is subjected. In this section brick 

 roads have been constructed directly upon the sand subgrade with 

 fairly satisfactory results. 



In this region ^vhere frost in the ground is unknown, it is neces^ 

 sary to provide only adequate bearing. The requirements of this 

 nature should, hoAvever, receive careful consideration and tj^pes 

 should be selected that can be repaired easily and successfully with- 

 out loss of good material, in case the assumed bearing value of the 

 soil is not developed in practice or decreases owing to deterioration 

 of curbs, drying out of sand, or other strictly local causes. 



Under the conditions usually prevailing neither the thickness of 

 the road crust nor the combined depth of surfacing and foundation 

 is adequate to prevent entirely the upheaval by frost, providing this 

 is sufficiently extreme. The question of combating frost action still 

 remains unsettled and exceedingly difficult of solution. The damage 

 caused by it is very great in some cases and the economic aspect of 

 the matter is involved. In general, it is not advisable to prepare 

 elaborate and costly foundations to save comparatively cheap roads 

 from slight damage; on the other hand, a considerable expense in 

 foundation construction would be' warranted if assurances existed 

 that the effect would be to save an expensive surface from all dam- 

 age. The entire question doubtless hangs on the reduction of soil 

 moisture in the premises and the removal of free water at all times. 

 To effect this the various methods of drainage discussed will serve 

 largely if judiciously applied. The use of shoulder drains and 

 ample provisions for relieving the subgrade and foundation near the 

 surface of melted snow and ice in periods of alternate thawing and 

 freezing will go a long way toward accomplishing the results de- 

 sired. Generally in the northern part of the United States, the gla- 

 ciated areas have well drained soils and frost action tends to be 



