. Bulletin of the Department of Agriculture. Agriculture; Agriculture. DRAINAGE METHODS FOR COUNTY ROADS. 47 be provided by means of a concrete foundation, and under extreme conditions of this sort concrete is practically the only satisfactory foundation material. (Fig. IT.) DESIGN AND CONSTRUCTION. No matter what type of foundation may be selected for a particular road or section of road it should, of course, be designed and con- structed with a view to meeting adequately the conditions involved. Since these conditions vary greatly, sometimes even on the same proj- . ect, it is manifestl
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. DRAINAGE METHODS FOR COUNTY ROADS. 47 be provided by means of a concrete foundation, and under extreme conditions of this sort concrete is practically the only satisfactory foundation material. (Fig. IT.) DESIGN AND CONSTRUCTION. No matter what type of foundation may be selected for a particular road or section of road it should, of course, be designed and con- structed with a view to meeting adequately the conditions involved. Since these conditions vary greatly, sometimes even on the same proj- . ect, it is manifestly impracticable to standardize either the design or construction of foundations except to a very limited extent. In the following discussion, therefore, no attempt will be made to do riiore than point out the limits of good design for each type of foundation and to describe, in a general way, what are believed to be the best methods of construction. Thus, unavoidably, much must be left to the judgment of those who design and superintend such work. Practical experience and observation disclose that the best roads usually have a great variety of foundations. These may have been. CONCRETE FOUNDATION Fig. 17. laid at the time of original construction, or added to meet conditions that arise from season to season. For long distances the changes often occur as frequently as every few hundred feet. Rarely are con- structed foundations now laid mile after mile, as was done formerly on the pikes of central Kentucky and elsewhere. The cost of such work is so great that the individual and local treatment has more generally been adopted by highway engineers. GRADING AND PREPARING THE SUBGRADE. The discussion on bearing power of different soils should be con- sidered in connection with what is said here regarding the proper method of grading a road and preparing the subgrade. The table of bearing powers given on page 41 is based on the assumption that the roadbed and subgrade will be prepare
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