38 BULLETIN iMj U. 6. DEPARTMENT OF AGRICULTURE. 
As shown in the cross-section drawing, figure 13. the V-drain is 
formed by excavating the subgrade 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 inchel in diameter down 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 may be compacted to form a 
firm, unyielding foundation for the road surface. The compacting 
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 the 
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. 
TThen 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 water 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 S inches is 
better. 
Outlets for conducting water away from the V-drain 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 a- 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 -table, whether or not outlets are provided. 
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 roadbed at these points becomes excessively soft, and both road- 
bed and surface soon are badly out of shape. 
