14 BULLETIN 463, U. S. DEPARTMENT OF AGRICULTURE. 
The question of minimum grade is of importance only as regards 
the side ditches. These should have adequate fall to empty the water 
that collects in them at a sufficiently rapid rate to prevent damage 
to the road. Ordinarily it is desirable to give the side ditches a fall 
of about 1 foot per 100 feet of length, though a somewhat less fall 
has proved satisfactory sometimes. 
Wherever changes in grade occur the change should be made by 
means of a vertical curve, and not by an abrupt angle. 
SLOPES. 
The slope at which earth will stand when faced up in a cut or 
placed in an embankment depends (1) on the character of the earth 
and (2) on the climate. In cuts, a good quality of nonslaking clay 
often will stand on a slope of about 45 degrees, or, as slope is 
expressed usually, 1 horizontal to 1 vertical, even where fairly deep 
freezing occurs, and in some of the Southern States such material 
has been known to stand for many years on a slope of less than one- 
half to 1. On the other hand, clay that slakes very easily may 
require a slope of 3 to 1. or even 4 to 1, under the most favorable 
condition of climate, but this latter extreme is very unusual. The 
usual slope for clay in cuts is 1 to 1 in warm climates and 1J to 1 
in cold climates. 
While in the case of embankments clay usually can be deposited 
on an initial slope of about 1 to 1, this steep slope seldom can be 
maintained unless the material is of an exceptional quality and the 
climate very favorable. Ordinarily clay embankments should have 
a slope of about 2 to 1 in cold climates and at least 1J to 1 in warm 
climates; and if the clay be of questionable quality these values should 
be increased. Embankment slopes require more care in construction 
than excavation slopes, because any flattening of an embankment 
slope by the action of weather after the road is completed is very 
likely to damage the road surface, while the sliding in of excavation 
slopes does no further damage than to obstruct the side ditches, 
which can be reopened readily. 
Sand of average quality generally requires a slope of about 2 to 1 
in cuts and 3 to 1 in embankments, regardless of climate. Moderately 
coarse sand mixed with gravel will stand on a steeper slope than 
fine sand, because the former is not moved so readily by the action 
of storm water. 
Solid rock excavation usually can be done on an average slope 
of about one- fourth to 1, except where the rock occurs in sloping 
strata separated by slippery clay seams. In the latter case the aver- 
age slope may be as much as one-half to 1 or three-fourths to 1. 
The faces of rock cuts, as a rule, are not dressed down to even an 
