Work of Maintenance Broken-Stone Road

WORK OF MAINTENANCE BROKEN-STONE ROAD. Under this head will be dis cussed the several kinds of work involved in taking care of a crushed stone road and in making repairs.

Raveling.

One of the chief evils to be contended with in the maintenance of a crushed-stone road is the tendency to ravel, i. e., for one stone after another to work loose on the surface. This occurs only after a long dry spell or in a road originally defi cient in binding power, and is more likely to occur on lightly traveled roads than on those having heavy traffic. Raveling may take place where the wind sweeps away the binding material from the surface, or on a steep grade where the water has washed the fine material away from between the fragments; and is chiefly due to the picking of the horses' shoes, and is in a measure coun teracted by the rolling action of the wheels.

At least three expedients are employed to prevent raveling. 1. Sprinkling the road with water effectually stops raveling, and causes the surface to solidify again. This is the most common remedy on city streets and suburban roads—where water is usu ally convenient and plentiful. For a further discussion of Sprink ling, see § 380. 2. A thin coating of coarse sand is very effective in preventing raveling. Ordinarily on country roads a layer half an inch thick over the middle 8 feet of the trackway is sufficient. Unless the season is very dry or the road is unusually exposed to the wind, a single application will be enough for one season; but in extreme cases two or even three applications may be necessary. It is important that the sand be reasonably clean and coarse, as otherwise it will be blown off by the wind or be washed away by occasional showers. If the sand is accompanied by iron oxide, all the better, as it adds to the cementing power and aids in pre serving an impervious covering, which tends to prevent evapora tion of the moisture below the surface. The coating should be very thick, or it will yield under the wheel and interfere with travel, besides being unsightly. The usual tendency is to add much sand, or to substitute loam or clay for part or all of the sand.

Clean coarse sand gives the best results. 3. The third method of preventing raveling consists in incorporating blue gravel or a small amount of hard pan or clay with the stone screenings used for surfacing the road during construction. The blue gravel and clay are high in cementing power, and when mixed with screenings make a hard and elastic surface which stands both wet and dry weather reasonably well, and does not allow the surface to ravel.

Ruts.

Next after raveling, the tendency to form ruts is the most serious evil to be contended against in the maintenance of crushed-stone roads. Ruts are due either (1) to a greater wheel load than the road is capable of standing, or (2) to the use of an inferior binding material, as loam, or (3) to tracking (§ 367). Ruts are most likely to occur in the spring or during a wet time, when the road-bed is soft, and are more common on country roads than on city streets, since in the latter the frequent changes in direction to avoid other vehicles produce a more uniform wear over the whole surface of the road. A street-car track in a broken-stone road prevents the distribution of traffic uniformly over the entire surface, and greatly increases the tendency to form ruts.

After ruts appear the only remedy is to fill them either with new material or by picking down the sides of the ruts and raking: the loosened material into the depression. Usually the latter course is the wiser, particularly on a new road. Frequently the tendency to form a rut may be effectually arrested by sweeping into it the loose detritus from the adjacent parts of the road. If the road surface is compact and hard, it may be necessary to loosen the bottom and sides of the rut before adding new material, so that the new will thoroughly unite with the old. The new material should be of the same character as the old, as otherwise the surface will wear unequally and become rough. For additional suggestions applying to this subject, see § 385.