EARTH, SAND-CLAY, AND GRAVEL ROADS. 



15 



approximately smooth slope, as is done in earth cuts. In excavating 

 solid rock only such material is moved as is actually necessary to 

 obtain the desired width at the bottom of the cut or as has been 

 loosened in blasting. The faces should, of course, be cleared of all 

 material which is loose, or which might be loosened subsequently by 

 frost and slide down upon the road. Stone embankments will stand 

 on a slope of about 1 to 1. 



In order to prevent damage by washing all earth slopes in either 

 excavation or embankment should be protected by a growth of grass 

 as soon as practicable after they are formed. 



In many localities where the soil is fertile and a good quality of 

 grass is native no seeding of the slopes is necessary. In other cases 

 the soil may not possess sufficient fertility to grow grass, even when 

 the slopes are seeded, and in which event it may be very desirable to 

 cover the slopes with cut sod. This latter process usually is very 

 expensive, and should be employed only where it is known that 

 thorough seeding and fertilizing would fail to secure a covering 

 of sod. 



Another precaution frequently necessary in order to prevent the 

 washing away of excavation slopes is to intercept water from the 



CROSS SECTION SHOWING BERM DITCH BUILT ABOVE SLOPE 



^Dimensions of the ditch are determined by the amount of water to be carried 

 C is generally 18 to 24" and "G" a bout 12". 



Fig. 10. 



natural ground surface which otherwise would flow down over the 

 excavation slope. This is done by means of a " berm " ditch con- 

 structed well back from the top of the slope. Figure 10 illustrates 

 a condition which makes a " berm " ditch desirable and also shows 

 how such a ditch is constructed. 



EARTH ROADS. 1 



Roads constructed by grading the natural soil to the required 

 shape, grade, and alignment, without special surfacing of any kind, 

 are designated as earth, or dirt, roads. The efficiency of such roads 



1 This section has been read and revised by P. St. J. Wilson, chief engineer, and T. War- 

 ren Allen, general inspector, TJ. S. Office of Public Roads and Rural Engineering. 



