FORMS OF CONSTRUCTION. There are two forms of con struction of country gravel roads, which differ as to the manner of preparing the subgrade to receive the gravel. In one form the gravel is simply deposited on the surface in a strip along the middle of the former earth road; and in the other a trench is excavated in which the gravel is placed. For convenience of reference the former will be called Surface Construction, and the latter Trench Construction.
SurfaceConstruction. The crudest form of this method of construction consists in dumping gravel, as it comes from the bank, in piles in line on an earth road. The quantity of gravel is gaged by dumping a load in one, or two, or three lengths of the wagon. Little or no attention is given to leveling off the top of the piles, and it is not rolled except as traffic is forced upon the ridge when the earth upon the sides gets muddy. For the first year or two after construction, such a gravel road is little if any better than an earth one. The surface is full of cradle holes and is easily cut into ruts; and the loose material absorbs the rain, and be comes mixed with the soil below. If the gravel is good, the road becomes fairly good after the gravel has been packed by travel and after the holes have been filled up by the addition of new material. This form of construction is common where gravel is plentiful, the work usually being done by labor road-tax.
Another form of surface construction consists in setting up two lines of plank on edge and filling the space between them with gravel. The gage planks are set on edge, 8, 10, or 12 feet apart according to the importance of the road, and the gravel is filled in between the planks, 8 or 10 inches deep at the sides and 12 or 15 at the center. Of course, when the boards are moved forward to be used again, the edge of the gravel spreads out and takes the natural slope, and under traffic it spreads out still further. Ordinarily in this form of construction the gravel is not rolled, and there is little or no driving over it by teams engaged in the construction. The only advantage of this method over the pre ceding one is that it affords a means of gaging the depth of gravel and of determining the quantity used; and the chief objection to it is that when gravel is put on in a thick layer, the lower part is not consolidated well, at least not for a considerable time, and therefore the surface is liable to break up. This form of construc
tion is very common.
In the best form of surface construction, the former earth road is first smoothed up with the scraping grader,—if necessary, reducing the crown. If after smoothing the surface with the grader, the foundation is not already firm and solid, it should be rolled. Next a layer of gravel 4, or at most 6, inches deep is spread upon the prepared subgrade, and leveled—either by hand with a shovel and rake, or with a harrow or scraping grader. In dump ing from a wagon or cart, the larger stones will roll to the outer edge of the heap, and in leveling the gravel, care should be taken that these are scattered and covered deeply with fine material, for otherwise the road will not have an uniform texture and will wear unevenly, and the large stones are liable to work to the .top.
If thy teams hauling the gravel are required to drive over that already placed, the road will be consolidated much sooner; but as the tractive resistance on loose gravel is very great, there is some disadvantage in this requirement. If it is to be insisted upon, the construction of the road should begin at the end nearest the gravel. The gravel can be consolidated with a roller, but not as effectively as by traffic, since no roller gives so great a pressure as the wheels of loaded wagons.* Heavy loads should not be permitted to go over the road while the surface is soft, for fear tin wheels will cut through and mix the earth and the gravel. While the gravel is being consolidated by the passage of the teams em ployed in the construction or by ordinary traffic, all ruts should be filled as soon as formed, by the use of a garden rake, and all holes should be filled by shoveling in fresh gravel. The cost of filling depressions and ruts will be more than saved in future repairs, while a much better road will be the result.