OF THE ROADWAY.
In places of great thoroughfare, there arc usually foot paths : indeed, for the protection and comfort of foot pas sengers, who form the greatest proportion of mankind, footpaths ought to he made along every bridge, and also every road. Nothing can be more degrading and unfair, than that those very persons, by whose labours bridges and roads are obtained, should be mixed with, and ex posed to be trampled on, by horses, or crushed by wheel carriages.
When the spandrels have been covered by arches or flat stones, it is only inc cessary, for the footpaths, to build with rubble stone foundations for the outside curbing. This curbing should be of hard stone, (say from 12 to 15 inches in depth ; and from 6 to 9 inches in thickness on the upper edge. Their lengths should be as great as can be conveniently procured, and they should be set in lime mortar. Tire space between tire curbing and the parapets, should be paved with hard flag stones, 3 or 4 inches in thickness, well faced and jointed. They should be laid in lime mortar upon a bed of coarse sand, or clean gravrl. In large bridges, the whole of the foot paths is sometimes covered with granite. The breadth of foot-paths varies from three to more feet: three feet will admit of one person walking with safety, four feet six inches will admit of two, and six feet of three. The top of the footpath should be from 6 to 10 inches above the bottom of the side channel. Along the outside of the curb stones, the French place borne or Ender stones ; but passengers, horses, and carriages, may get entang led and injured by them; it is therefore preferable to have small paving stones set, forming an inclined plane between the outer edge of the curbing, and the bottom of the side channel : this will effectually prevent carria ges from coming upon the foot-path.
If the carriage way is to be paved, there should he laid upon the covering of the spandrels, and over the top of the arches, a bed of gravel mixed with loam, about from 12 to 18 inches in thickness, worked with water into the consistence of mortar. When this has become moderately dry and firm, squared whin paving stones, about four inches square, and six to eight inches in depth, are to be set and well beat, making a curve across the road of four inches in 24 in breadth ; and that. curve should be terminated by sinking four inches more in the distance of two feet from the inclined plane, which has been formed along the outer edge of the curbing stories.
If the roadway is to be made with gravel only, it is necessary to lay it 22 inches in depth in the middle, and 18 inches near the sides : It should contain a small mixture of loam, so that when worked with water, it shall consolidate and afterwards exclude water. There should still be about 18 inches in breadth, on each side next the before-mentioned inclined planes, paved with small squared whinstones ; because, by forming the roadway a little convex across, and with a declivity of 1 in 24 lengthwise, it is meant that the greatest pro portion of water which falls on the bridge shall run along each side.
In small bridges where there are no cavities in the spandrels, it is necessary to fill them up with coarse gravel with a mixture of loam, working it with water as put in ; and if this simple operation is carefully perform ed over the arches, the trouble and expence of coating with cement, and other substances, may safely be spared.
The water which falls upon the roadway of the bridge, must be conducted beyond the extremity of the wing walls, and be there introduced into covered drains, or open paved sewers, and be afterwards carried off in the most convenient direction.
In or adjacent to towns, walls or quays are usually carried from the abutments along the banks of the riv er ; and even in the country it is frequently found to be advisable for protecting the abutments ; but as the de scription of this sort of work falls more properly under that of wharfs, we shall refer the reader to the articles IlAnnoun and INLAND We have knolsn bridges, whose arches were of con siderable size, consti ucted with bricks. In this case, it is customary either to have the whole of the piers, or at least the upper points cased with stone ; but if the points are circular, and bricks made of a suitible shape, and outside bricks laid headers in British cement, the work will be sufficiently substantial. It is necessary that the bricks for the whole bridge be made of good clay, well prepared and tempered, he burnt hard, and laid with thin beds of mortar, but to be properly flushed as they are laid, and grouted afterwards. It is likewise neces sary, after the arches are closed, that the centres be suf fered to remain until the mortar has acquired a consi derable degree of consistence. It will greatly improve the work, if laths or loop iron are laid in as it advances.