8 BULLETIN 220, U. S. DEPARTMENT OF AGRICULTURE. 



requires it. All hollows and depressions which develop during the 

 rolling should be filled with good material. If soft or spongy places 

 develop during the rolling, the soft or spongy material should be 

 taken out and replaced with good material and the subgrade again 

 rolled. This process of filling and rolling is repeated until no depres- 

 sions develop and the subgrade has been brought to its proper ele- 

 vation, which is as much below the established grade as the thickness 

 of the surfacing course to be used. The shoulders ought also to be 

 rolled in the same manner, but in places where the character of the 

 material makes the use of a heavy roller impracticable, a lighter 

 roller may be used. The shoulders are built at the same time as the 

 subgrade and with it form a trench to hold the surfacing material. 

 They may be built either by excavation or by piling up earth as the 

 work progresses. The shoulders also serve to widen the road for the 

 passing of vehicles. They are usually given a sharper slope than 

 the paved portion of the road. 



Plate V, figure 1, shows a model illustrating several methods of 

 road drainage. It will be noted that the roadbed is located partly in 

 a cut and partly on a sidehill. 



Section A shows a surface ditch (h) at the top of the slope, a side 

 drain (c) opening into a culvert (a) with a drop inlet (b), a telford 

 base, a section of guard rail (g), and a shoulder drain (d). 



The surface water falling on a large area sloping toward the road is 

 often kept from the road and out of the road gutters, where it usually 

 does considerable damage, by a surface ditch such as (h). The side 

 ditch (e) is used to gather the water originating on or along a roadway 

 and to carry it to points of outlet. As a general rule the bottom of 

 the ditch is lower than the low point on the subgrade of the road. 

 The size of the ditch varies with the amount of water it is necessary to 

 accommodate. The shape of the ditch varies with climatic, soil, and 

 topographic conditions. The side drain (c) is constructed to carry off 

 the ground water which is often found in hilly sections. In the model 

 the trench is represented to be 2 J feet deep, 12 inches wide at the 

 bottom, and 18 inches wide at the top. On the bottom of the trench 

 is placed tile pipe, usually 6 inches in diameter. The pipe is laid 

 without cement, and loose stone is carefully filled around the sides 

 and top of the pipe to the top of the trench. The side drain empties 

 in some suitable outlet. For example, the one in this model empties 

 in a drop inlet (b), which also serves as an outlet to the surface and 

 side ditches. The drop inlet empties into a culvert (a) , which carries 

 the water under the road. This type of inlet prevents the bank from 

 sliding and closing the culvert, which sometimes happens in hilly 

 sections. 



The purpose of the shoulder drain (d) is to permit water to escape 

 from the subgrade during or immediately after the construction of a 



