528 



A TALK ON ROAD MAKING. 



road-bed iS inches thick. Its construction consists in 

 first laying a foundation of any rough rubble-stones of 

 convenient size for handling, and placing them carefully 

 by hand in parallel courses across the road-bed as for a 

 rough street pavement. The nearer such stones can be 

 brought to the general form of paving-stone by judicious 



under the horses' feet. The heavier the draft the greater 

 the disturbance will be. Another defect is the frequent 

 turning necessary, and the impossibility of packing firmly 

 the parts of the road where the horses turn. For ordi- 

 nary cemetery use a steam-roller of from 5 to lo tons will 

 suffice. In compacting the surface coat, frequent sprink- 

 ng is also necessary. Both sprinkling and 

 rolling should be continued together or alter- 

 nately until the surface becomes perfectly solid. 

 If, finally, the water from the sprinkler be all 

 shed into the gutter by a water-tight surface, 

 so much the better. 



Fig. I.— Construction of GurrhR, Cop:ng and Pavement. 



breaking, the better the work. Blocks averaging 6 inches 

 in thickness by 12 inches in depth will make strong work, 

 however rough their general shape. They should be 

 placed on edge, with the largest edges down, and be set 

 as closely and firmly together as their rough shape will 

 permit. Where the jagged upper edges project too high 

 for the established thickness of the layer, they should 

 be broken off, and all low places should be filled with 

 suitable chips well packed into place. The whole course 

 should be gone over, and all open spaces be filled by 

 ramming stones of suitable sizes into all interstices with 

 pounders or heavy hammers. When the surface is level 

 enough for rolling, the heaviest roller obtainable should 

 be used, and the rolling be continued until the whole 

 foundation course is perfectly solid and of the right shape 

 and height to receive the Macadam course ; that is, the 

 course of small stone. 



The depth of this course of small stone will vary with 

 the same circumstances which determine the whole depth 

 of the pavement. Usually it is about one-third of the 

 whole. Thus it will be 4 ir.ches thick if the Telford 

 course be 8 inches, and 6 inches if the foundation be 12 

 inches deep. The stones may be laid in two courses if 

 the depth be 6 inches, and each course be rolled separ- 

 ately. For the lower course the stones should all be 

 small enough to pass through a 3-inch ring, and through 

 a I'/^-inch ring for the upper coat. To make at once a 

 smooth and firm surface it should be dressed with an inch 

 of fine stone screenings or selected gravel of similar qual- 

 ity. This should contain some fine sand or earth loam, 

 just sufficient to sift into the finer chinks and to bind the 

 Macadam stones into one firm crust when well watered 

 and rolled. 



For the best work a steam-roller is necessary at every 

 stage, and each course should be rolled until no further 

 impression can be made, or, in other words, until the 

 roller leaves no track behind it. Horse-rollers, however 

 heavy, are very inferior, because the stones shift so easily 



A common error in road-making is to have 

 the pavement too shallow. It must be strong 

 enough to withstand the heaviest traffic to 

 which it may be subject, without yielding when 

 the frost thaws out in the spring. Where the 

 subsoil is exceptionally sandy or gravelly a 

 depth of from 6 to 9 inches might answer fair- 

 ly well, but under ordinary conditions a 12 to 

 18-inch depth is necessary for a cemetery roafj 

 subject to much travel, while public highways should 

 ordinarily be still thicker. Few are aware of the great 

 difference in power to support a load between a firm 

 layer 6 inches in depth and a compact mass 18 inches 

 deep. The surface pressure of the passing vehicle will 

 spread through either layer, as shown in fig. 2, in the 

 form of a cone with its apex at the wheel and its base on 

 the road-bed. The area of this base will increase (to 

 use an engineering term) " as the square of the depth." 

 Thus, if the depth of the stone be 6 inches, the weight of 

 the road-bed under the stone will be over 36 inches. If 

 the depth be 12 inches the base will measure 144 inches ; 

 if 18 inches deep the weight will spread over an area of 

 324 square inches. Thus a pavement of 18 inches is 

 nearly ten times as strong as one of 6 inches, instead of 

 being only three times 

 as strong, as most peo- 

 ple would naturally sup- 

 pose. In a like ratio is 

 the power to resist the 



I 



/' ! 6 INCH BE P upheaving of frosts, es- 



I \ pecially if road and 



; '\ r o a d - b e d be w e 1 1 



'\ IS INCH BE D drained. 



I \ The question of depth 



/ I '\ being decided for any 



/ i 18 INCH BED . ,, 



' ~~" given case, the excava- 



H1G.2.— Showing HOW THE strength |.;qjj jjjg sub -grade 

 OF A ROAD IS proportional ,^ cox^ioxm as 



to its thickness. 



nearly as possible to the 

 established grade of the finished road, both in profile and 

 in cross-section, as shown by fig. 3, on the next page. 



The proper form of the finished surface will vary con- 

 siderably as the grade varies. On a nearly level grade 

 the height of the center above the edges of the gutter 

 should be in the ratio of i to 25. This will give a crown 

 of 6 inches for a 25-foot road, or 12 inches if the width 

 be 50 feet. If the grade be steep, the crown should be 



