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- 
r 
^%00® Cross section ready to receive the surfacing material 
\ r B to 1 inches 
.6 to 8 inchles 
WmihMMMMk^fMM^Mk^S B 
T 
Cross section of completed road 
TYPICAL CROSS SECTIONS SHOWING METHOD OF CONSTRUCTING 
A SAND -CLAY ROAD, USING T0PSOIL OR OTHER NATURAL MIXTURE. 
W' should be at least 10 feet for single track road and "S" generally notjess 
than 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 lG-foot sand-clay 
