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 vrhen 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 H 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 1^ 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 



