In many cases where roads are to be constructed along steep slopes, it is found cheaper to use retaining walls to sustain the road upon the lower side and the earth cutting on the upper side than to cut long slopes or form high embankments.
Catch-water drains are necessary on the natural sur face above the top of all high slopes in cuttings to prevent the surface water from washing down and destroying the face of the slope.
Where springs are tapped by a cutting, drains must be provided to remove the water without injury to the slope; and where the subsoil may become wet in rainy weather, it may be necessary to provide sub surface drains along the slope to prevent the earth becoming saturated and sliding down into the roadway.
Slopes, both of excavation and embankment, are greatly improved by being sodded or sown with grass.
This aids in the maintenance of the slopes, by render ing them more capable of resisting the abrading action of such water as falls upon them. It also greatly improves their appearance.
The most important principle involved in the forma tion of a road-bed, which should be always in mind, is that earth, in order either to sustain a load or to main tain a slope, must be kept dry, or at least prevented from becoming saturated with water, as both the cohesive and frictional resistances of earth are dimin ished or destroyed when it becomes wet, and it is also then liable to the disturbing action of frost.
Methods of Handling Earth. In the grading of roads or streets, the earth is commonly moved by scrapers, or wagons, after being loosened by plowing. For ordinary work the common railroad plow is used, drawn by two, or in hard material four, horses. In breaking up very hard material, like an old gravel surface, a rooter plow may be needed with four or six horses. Economical handling of the material requires that it be well loosened and the plowing is usually but a small part of the cost.
For moving the loosened earth, drag scrapers may be used for short ' hauls; they are economical for distances up to about no feet. . For distances greater than about 8o to No feet wheel scrapers will be more economical; for the shorter hauls, the small (number t) scraper, with a single team to handle each scraper; for longer hauls, above 200 to 300 feet, the larger (number 3) scrapers, with snatch teams to load them.
For hauls greater than about 50o to 60o feet, wagons, loaded by men with shovels, will usually be cheaper than scraper work.
In flat country where the grades conform closely to the natural surface, and the road-bed is formed with earth taken from the side ditches, the use of the eleva ting grader is usually economical and frequently makes possible the construction of the road at very low cost. This consists of a frame resting upon four wheels, from which is suspended a plow and a wide traveling belt. The plow loosens the earth and throws it upon the inclined belt, which carries it to one side and de posits it near the middle of the road. The ordinary machines are built to deliver the material at about 14 and 17 feet horizontally from the point at which it is excavated. They are usually operated with eight horses.
The ordinary road machine, or scraping grader, is also a convenient tool for this kind of work, and when the amount of material to be moved is small, and the work consists in cutting shallow side ditches and form ing a road surface with material taken from them, is usually the most economical tool to employ.
Work done by scrapers will usually be left in rough and lumpy condition. For smoothing the surface, after the earthwork is roughly completed, the scraping grader or some form of road leveler may be used. For this purpose the blade is set so as to cut off the tops of the ridges and lumps, and fill up the hollows, with out carrying along any earth.
Work Required in Moving Earth. The work required for moving earth under approximately the same conditions differs widely in practice. It depends upon the character of the material, the methods adopted for the work, the kind of labor available, and, most important of all, the skill with which it is managed.
Loosening. In .ordinary compact soil a plow and team with driver and plow holder will loosen 30 to 40 cubic yards per hour. If the material be very hard, an extra team and man will be required for about the same, or a little less, amount of earth; while in hard buckshot, or in breaking up an old road surface, not more than one-half the amount may be loosened.