194 



EARTHWORK 



rate -of side slopes and width of ditches is required for single- 

 track work, the width for double-track work must be 13 ft. 

 greater. When excavation is made through rock, the side 

 slopes of the ditches may properly be made much steeper; 

 the danger of scouring during heavy rain storms being elimi- 

 nated, the total required width may be very materially reduced 

 from the figures just given. The heavy expense of excavating 

 through solid rock requires that such economy shall be used 

 if possible. 



Grade Profile. For the purpose of constructing a road as 

 well as for calculating the earthwork, a grade profile is pre- 

 pared by setting stakes on the center line at every full station 

 and also at all intermediate points at which the inclination 

 of the natural surface of the ground changes abruptly; then, 

 by leveling, the elevation of the natural surface at each stake 

 is determined and plotted, as explained under Leveling. The 

 established grade is then drawn in. It consists of a series 

 of straight lines, the elevations of the ends of which are clearly 

 indicated. These elevations are those of the subgrade ac, 

 Figs. 1 and 2. 



A short portion of a profile is shown in Fig. 3. The horizontal 

 line XX' represents a reference plane, and the broken line 



AGH shows the position of the established grade. The sta- 

 tion numbers are written along the line XX', and the eleva- 

 tions of the corresponding points of the established grade are 

 written along the grade line. Thus, in Fig. 3, the elevation 

 of subgrade at Sta. 90, or A , is 100 ft. ; at Sta. 93, or G, it is 

 102.28 ft.; and at Sta. 94, or H, it is 101.78 ft. 



The gradient of the established grade is the per cent, of rise or 

 fall of grade; that is, the number of feet by which the elevation 



