44 



BULLETIN 463, U. S. DEPARTMENT OF AGRICULTURE. 



consists of clay which is not considered suitable for use in the sur- 

 face, it is well to spread the sand layer first and to make its depth 

 more than is sufficient for use in the surface. The surplus sand 

 which remains under the completed surface then will serve to improve 

 the drainage of the road. 



Plate IV, figures 1, 2, and 3, illustrates the several principal 

 features involved in the construction of a sand-clay road and supple- 

 ments the information given in the text. 



COST OF SAND-CLAY ROADS. 



From the foregoing discussion of construction methods, it is 

 apparent that the conditions under which sand-clay roads are con- 



^%0^ Cross section ready to receive the surfacing materia! 



^wwJXm 



\ r 8 to 10 inches 



Cross section of completed road 



TYPICAL CROSS SECTIONS SHOWING METHOD OF CONSTRUCTING 

 A SAND -CLAY ROAD, USING TOPSOIL OR OTHER NATURAL MIXTURE. 



"W' should be at least 10 feet for single track road and"S"generally notjess 

 thart 5 feet, for double track. "W" should be not less than 14 feet and "S"not 

 less than 3' feet 



"H" crown, vanes from % to the foot for level grade, to I " to the foot for 

 a grade of 5% 



Fig. 21. 



structed vary over a wide range, and that any general statements 

 regarding costs may be very misleading when applied to a particular 

 case. In general, for a cost estimate to be at all reliable it should 

 be arrived at by considering the following items: (1) grading and 

 preparing the subgrade, (2) excavating and loading surfacing ma- 

 terial, (3) hauling surfacing material, (4) mixing and shaping 

 surfacing material. 



Table 8 shows the cost of these items for several different sand- 

 clay roads which have been constructed under the supervision of 

 the Office of Public Roads and Rural Engineering and may be of 

 some assistance in preparing estimates of probable cost for similar 

 projects. As a matter of general information it may be stated that 

 in the Southern States the cost of constructing 16-foot sand-clay 



