Page:Popular Science Monthly Volume 51.djvu/87

Rh policy of the commission to reduce all grades to a maximum of five feet in one hundred—called a five-per-cent grade. After courses and distances are plotted, and the necessary data obtained for determining the quantity of the various materials used in the construction of a road, a conference is held between the petitioners and the State commissioners, in order to ascertain if a contract for the construction of the road is to be made by the municipality, and, if so, at what price it is to be done. In case the city or town authorities are unwilling to contract for the work upon the prices agreed, the commission advertises the same, and it is let to the lowest responsible bidder, subject to the approval of the Governor and Council. It is the custom in awarding competitive contracts to require the contractor to furnish bonds: one insuring a faithful completion of the work; the other to safeguard the interests of the town or city in case damage results from accidents during the building of the way. Upon the contract being made and a notification being received that the municipality or contractor is ready to proceed with the work, the commission appoints a resident engineer, who has personal charge of the work of construction, subject only to the supervision of the chief engineer.

Now comes the period of actual construction, and the first step in advance is the excavation and filling the road to the required subgrade. In general the subgrade is about nine inches below the finished grade; but the extent of excavation differs widely in actual practice, owing to the different treatment necessary as determined by the varying character of the ground. The subgrade established and rolled, broken stone is then added to a depth of six inches, the fragments varying in size from one and a quarter to two and a quarter inches in their longest dimension. This is then rolled with a steam roller until thoroughly compacted (Plate I). A second layer of broken stone, three inches thick, is next spread upon the road, the pieces ranging in size from one half to one and a quarter inch. This is then rolled as before, and a finishing coating of screenings, put through a half-inch mesh, is then added to a depth of half an inch. Water is now turned on until the broken stone is well wet down, when the final rolling is done, and the surface becomes firmly and smoothly knit together (Plate II). In the foreground of this picture the second layer of broken stone is seen. The main part of the road is in its completed state, having just been compacted with the steam roller. Some modifications are made in these steps of the process, depending upon the quality of the stone used and the amount and kind of travel to which the road is to be subjected. As pointed out by Macadam, it is not wise to place a layer of broken stone directly upon a subgrade of granite