148 



AGRICULTURAL ENGINEERING 



if there is water beneath it the water will come up by capil- 

 lary action and soften the road until its supporting power is 

 lost. Again, the action of frost is greater when the road sur- 

 face is full of water. Freezing causes the roadbed to expand 

 and heave, tending to soften it. Thus it is highly important 

 that soil in which the ground water stands within 3 or 4 feet 

 of the surface be drained with a tile drain. This is generally 

 accomplished by placing a line of tile at one side of the road, 

 under the side ditch, although sometimes it is placed beneath 

 the middle of the road. The former location is preferable 

 for several reasons. First, the ditch does not need to be as 

 deep. Second, in case of repairs the tile is easier to get at 

 than it would be if it were located underneath the middle of 

 the road; and, if it is found necessary to take it up, traffic will 

 not be interfered with. Third, in a properly constructed 

 earth road the water which flows on the surface is conveyed 

 rapidly to one side by the slope or crown of the road. 



FIOST CLASS 

 Section m Cut 



Crown-!' per root 



Fig. 



CLASS 



Section in Fill 



79. Cross sections of earth roads, as recommended by the Iowa 

 Highway Commission. 



Where thorough drainage is needed, it may bfe advisable 

 to place a tile line at each side of the road, but under ordi- 

 nary circumstances one line of tile ought to be sufficient. In 

 providing tile drainage, care should be taken to see that the 

 tile is of ample size to meet the requirements of the area to be 



