28 



BULLETIN 124, U. S. DEPAETMENT OF AGEICULTUEE. 



The cost of stone masonry for siicli striictnres varies from about 

 $6 to about $12 per cubic yard, according to the amount of difficulty 

 experienced in obtaining the stone. 



SUBDRAINAGE. 



In addition to the side ditches, gutters, etc., required for draining 

 storm water awav from the surface of a road, it frequently is neces- 



3'-4" 



'"i 



B-B 



^ 9" 



-I0"-*| 



CONCRETE T END WALL 



FOR PIPE CULVERTS 



Fig. 10a. 



PLAN 



sary to provide a system of subdrainagc to lower the siu-face of the 

 ground water under the road. The elevation of the ground-water sur- 

 face depends on the capillary power of the soil and the hydrostatic 

 pressure to which the ground water is subjected, and under some com- 

 ])inations of soil and topography this elevation may be such as to 

 destroy the stability of the roadbed unless subdrainage be provided. 

 The common methods of providing subdrainage are, first, by open 

 ditches; second, by ditches filled with broken stone or gravel; third. 



