EARTHWORK 



193 



in a fill is 1^ horizontal to 1 vertical. When a fill is made of 

 the material from a rock cut, it is possible to make a stable 

 embankment with a slope ratio of 1:1. On side-hill work, 

 where a slope ratio of 1$:1 or even 1:1 might require a very 



FIG. 2 



long slope, it is often advisable to make a rough dry wall of 

 the stones from a rock cut that will have a slope ratio of 

 3:1, or it may even be steeper. 



Width of Excavations and Embankments. The width 

 required for a standard-gauge single-track roadbed may be 

 estimated as follows (see Figs. 1 and 2): The tie will be 

 between 8 and 9 ft. long, usually 8 ft. 6 in. At the ends of 

 the ties, the ballast will slope down to subgrade. The extra 

 width required for this will be about 1 or 2 ft. at each end 

 of the tie. Usually, the embankment is widened for about 

 2 ft. beyond the ballast on each side. The absolute minimum 

 for the width of subgrade for a fill is, therefore, 8$ ft.+2X 

 (1+2) ft., or about 14 i ft. This width would be used only for 

 light-traffic, cheaply constructed roads; 16 to 18 ft. is far more 

 common, while 20 ft. and even more is frequently used, as 

 the danger of accident due to a washing out of the embank- 

 ment is materially reduced by widening the roadbed. 



In cuts, the proper width for two ditches should be added. 

 Unless the soil is especially firm, the ditches should have a 

 side slope of 1.5:1. If the ditch is 12 in. wide at the base and 

 12 in. deep, with side slopes of 1.5:1, each ditch will require a 

 total width of 4 ft. This will add 8 ft. to the width of the 

 cut at the elevation of subgrade. The usual distance between 

 track centers for double track is 13 ft. Therefore, whatever 



