38 BULLETIN 724:, U. S. DEPAETMENT OF AGRICULTURE. 



As shown in the cross-section drawing', figure 13, the V-drain is 

 formed by excavating the subgracle of the road so that its cross sec- 

 tion will have the shape of a flat V. This V-shaped trench is filled 

 with field stone of all sizes from 6 to 8 inches in diameter clown to 

 pebbles only about 1 inch in diameter. The larger stones are placed 

 in the center and lower part of the trench, while the smaller are 

 placed on top and near the edges. It usually is necessary to spread the 

 stone in two or more courses, so that it niaj be compacted to form a 

 firm, imyielding foundation for the road surface. The conipacring 

 should be done with a power roller weighing about 10 tons, but should 

 not be carried to such an extent as to fill the interstices between the 

 stone in the lower part of the drain and thus prevent water from 

 finding its way along the trench. 



Some designs for V-drain, in order to save stone, require that tlie 

 drain be carried out practically to depth at the extreme edges, so 

 that the stone or other road metal is practically without drainage at 

 those points. 



When V-drains of this design have been used in northern localities 

 difficulty has been experienced with the edges of the road crust heav- 

 ing in the spring. Probably this is due to the freezing of accumu- 

 lated water near the edges of the drain. Such water will accumulate 

 in the interstices as a result of shallow thaws that do not free the 

 deeper areas of frost. The melted snow can not run off and fills 

 the upper layers of the V-drain, especially near the edges, until the 

 voids are too full to allow expansion on freezing. The result is that 

 during succeeding freezes the edges of such drains will heave. The 

 remedy is to increase the depth of V-drain at the edge and to provide 

 drainage close to the surface through the shoulder so that such drains 

 certainly will clear with the shallow thaws and permit Avater to flow 

 freely from the V-drain. Experience indicates that the depth of 

 V-drain, in addition to the surfacing material, should not be less 

 than 4 inches at the edges, and that a depth of 6 or 8 inches is 

 better. 



Outlets for conducting water away from the V-clrain should be 

 provided at all low points in the grade. These outlets may consist 

 of tile running from the lowest point of the V to a culvert or cross 

 drain, or of ditches filled with the same kind of material as that 

 composing the V-drain and running from the lowest point in the V 

 to any lower point outside of the road where they may empty. In 

 low flat sections, it frequently is difficult to provide suitable outlets 

 for drains of any kind, and because V-drain foundations give the 

 appearance of being very stable, whether or not outlets are pro Abided, 

 this feature sometimes is neglected in their construction. The result 

 of such neglect is that water collects at low points in the grade and 

 the rdadbed at these points becomes excessively soft, and both road- 

 bed and surface soon are badly out of shape. 



