Road Making Systems

The following extraets from The Engineering and Building Rccord's prize essay on road making (y 8. C. Thompson. New York) contain many valuable f acts: Where curves are mjuired inake them as flut as possible, and on a ñrst class road, where long trucks or loadg ai'e liablu to come, only in extreme eastw should it exceed a curve of ftfty feet radius. Ou mountainous roads it sometimes becomes necessary to increase the curve to ix radius of twenty feet. A man can walk up a slope of 100 in 180, and a horse or mulé can ascend an incline of 100 in 175, and it ha3 been found by exeriment that a horse pulling his maximum load on a level can pull but four-fifths as mnch if the slope Is made 1 in 50, and this gradually lessena until with a slope óf 1 in 10 he can draw but one-fourth os much ás hls luvel load. The maximum grade established by the French Government Board of Engineers is 1 in 20. The Holyhead road in Wales uses 1 in 80 as a maximum, except in two cases. Tho road over the Simplón Pasa averages 1.22 on Italian side, and 1 to 17 on Swiss side, with one case of 1 to 13, and in thls state several turnpiko roads are limited by law 1 in 11. In laying out a road, with regard to grades, havo a continuóos inclinatíon in one direction, and do not allow any counter grades, for, in ascending, each foot descended on a counter grade ineans just so much more rise to be overeóme. Where a long inclino becomes necessary it will be found economical to mako tho first portion the steepest and decrease it as it ascends, and if the slopo can be varied by occasional level stretches tho efficiency of tho road will be greatly increaséd. The roadbed on steep slopes is subject to greater wear from the feet of horses in ascending, and is much more subject to serious erosión by heavy rains. Where the roadway is too wide it usually results in no part being kept in good repair, whilo if it was narrowed the whole oould be kept in flrat class condition at leas expense, and a well kept road oí even twenty feet width is far preferuble to a road but half inaintained of doublé the width. In laying out it may be advisabje to take a strip considerably wider than the intended roadbed, so as to provide for possible contingencies in the future when the land becomes more valuable. Lay out sufficiently wide, bat build only so much as eau be kept in thorough repair. The essential requirements of a good roadbed are that it shall be practically unyielding - smooth on the surface, and impervious to water, and without these requirements there can be but little durability. No matter what the material may be, a proper attention given to drainage will be found to be a good iuvestment, both as to first coat and future maintenance. In this climate the worst enemies to building or properly maintaining a roadbed are water and frost, and if the first is kept out the second will have little or no effect, as the surfaco will not ba affected, and heaving will be reduced to a minimum. Again, if a roadbed is thoroughly drained it dries much more promptly, and has less mud and less duat. For earth roads, as coiumonly built, there is but little to be said, and they should only be tolerated in a new country or where there is absolutely nothing but earth of which to maké a road. Yet with earth alone a very passable road can be made and inaintained, if sufiicient care is taken to havo it thoroughly drainêd and tho surface of proper shape. The persistent care with which some of the so called roal surveyors in tho country excávate the material which has washed into the gutters and replaco it upon tlie center of the road seenis to indícate a belief that the powers of man surpass and are superior to those of nature. For surface draming, ditches should be provided along each side of the road having sufiicient f all to promptly carry away any water that reachea them. Where it becomea necessary to carry the water across the roadway culverts should be provided. All draina should have a continuous fall throughout their entire length, and the sizo will depend upon the inclination and the amount of water they are expected to carry. In portions of the country where gravel is easily obtainable a very satisfactory road can be made by making the surface for a greater or less depth of gravel. Prepare the foundation so as to allow for prompt drainage, and shape as the flnished road is in tended to be; make the sides of the road planes, and not curves, and then roll thoroughly to get a solid foundation. Put on a layer of gravel from six inches to eight inches in thickness. sprinkle thoroughly and roll till very compact and firm. Next spread another layer from four to six inches of gravel, and sprinkle and roll till the desired hardnesü and smoothness are obtained. If the gravel has no binding material in it, a sufficient amount may bo ineorporated in the last layer to cause it to take a good bond. Where it is possible to get blue gravel or hard pan and clean bank gravel, the two can be so mixed as to give a surface almost like concrete in hardinesa. When the two are usod together a two horse grooved roller for the first layer will be found very effective, and the material should be quite wet while rolling. The surface can then be finished with a steam roller, or with a smooth roller sufflciently loaded to givo the requisite weight. In completing the surface of a gravel, or other road, where rolling is required, the weight of the roller should bo as much per inch as the weight per inch on the tire of the hoavieet vehicle likely to pass over it. For ordinary trafflc a very durable and económica! surface can be produced in this way.