« AnteriorContinuar »
road should be constantly kept open, and free from weeds.
Those parish roads which are very narrow, and whose surface is below the level of the adjoining fields, and on which streams of water are constantly running, should be new made, by raising them with earth, and forming a roadway of good materials on the embankment.
The business of repairing a road should always be managed on a regular and fixed plan.
The following matters require particular attention : —
1st. The quality of materials.
2d. The quantity to be put on per mile per annum.
3d. The preparation of the materials.
4th. The method of putting them on the road.
5th. The number of labourers to be employed.
1st. With respect to the quality of the materials to be used: the hardest should always be preferred; for it should ever be borne in mind that hard stones brought from a distance are found by experience to be cheaper in the end than those of a softer kind which may be got near the road at a much lower price.
Another reason for making use of the hardest materials that can be procured is the greatly increased labour of horses, which is occasioned by working into a smooth surface often renewed coatings of weak materials. With respect to the subject generally of road materials, it may be observed, that the best descriptions consist of basalt, granite, quartz, syenite, and porphyry rocks.* The whinstones found in different parts of the United Kingdom, Guernsey granite, Mountsorrel, and Hartshill stone of Leicestershire, and the pebbles of Shropshire, Staffordshire, and Warwickshire, are among the best of the stones now commonly in use. The schistus stones will make smooth roads, being of a slaty and argillaceous structure, but are rapidly destroyed when wet, by the pressure of wheels, and occasion great expense in scraping, and constantly laying on new coatings. Limestone is defective in the same respect. It wears rapidly away when wet, and therefore, when the traffic is very great, it is an expensive material. Sandstone is much too weak for the surface of a road; it will never make a hard one, but it is very well adapted to the purpose of a foundation pavement. Flints vary very much in quality as a road material. The hardest of them are nearly as good as the best limestone, but the softer kinds are quickly crushed by the wheels of carriages, and make heavy and dirty roads. Gravel, when it consists of pebbles of the hard sorts of stones, is a good material, particularly when the pebbles are so large as to admit of their being broken; but when it consists of limestone, sandstone, or flint, it is a very bad one; for it wears so rapidly that the crust of a road made with it always consists of a large portion of the earthy matter to which it is reduced. This
prevents the gravel from becoming consolidated, and renders a road made with it extremely defective with respect to that perfect hardness which it ought to have.*
* The following is a description of an experiment that has been made of the use of iron materials, in the shape of small cubes, mixed with broken stones: —
Road made partly with broken stone and partly with pieces of cast metal, laid on over a sub-pavement of rubble stone.
This plan has been lately tried on a part of the Holyhead Road between London and Birmingham, and appears to possess some important advantages, which, however, can only be ascertained with certainty by a trial on a more extended scale, and in a situation where there is a much greater thoroughfare of horses and carriages.
The plan simply consists in laying on pieces of cast metal on the surface of a road, previously well constructed in the manner recommended by Mr. Telford, and adopted in all the new works on the Holyhead Road; that is, with a rubble pavement of large stones, covered with six inches of good hard broken stone. This layer of stone should be laid on in two successive operations; the first coat should not be more than three inches thick, and which should be kept constantly raked until it became nearly consolidated; the second coat should then be applied, and raked in very carefully the moment a carriage track appeared in it. When this coating becomes consolidated, so that a carriage could pass over it without leaving a rut, the iron may be applied. This may be done by a labourer. He should be provided with an iron instrument similar to a marline-spike, and about twelve inches long; the upper six inches should be round, and the lower six should be tapered down to a square point. With this tool and a mallet a hole should be made in the road large enough to receive the cube of metal, which should be stuck firmly down, until the upper surface of the iron is on a level with the surface of the road. The stone chip caused by making the hole should then be packed round the iron, and
2dly. With respect to the quantity of materials to be put on a road in the course of a year: this should be regulated by the traffic and the durability of the materials. The object to be secured is, to give the road a degree of strength sufficient to make it smooth and hard, not only in ordinary wea
beat down by the mallet. One of these iron cubes should be placed in the manner above described in every four square inches of surface, and the road, if the work be done in summer, should be frequently and copiously watered, until the iron cubes become perfectly fixed and firm in their places, which will be the case in three or four days, even with a limited traffic over the road.
It was in this way that the experiment was made on the Holyhead Road; the cubes of iron were put in in the month of March 1835, and became consolidated in about three days: very few were thrown out of their places by the horses' feet or the wheels of carriages during that period; and after they became consolidated there was not one observed to move. They have been now on the road two years, and they appear to have suffered scarcely any wear. The road has remained in a very perfect state up to the present time; and during the whole of the last winter, which was singularly unfavourable for roads, it has required scarcely any scraping, and no repairs whatever from the first time it was laid down. There is nothing in the appearance of the road to indicate that it is at all different from common stone roads, and it requires a close examination to detect the iron. The horses do not slip in the least, and the wheels of carriages pass over it apparently with great ease of draught.
In streets iron may prove of great advantage, as it will certainly diminish to a great extent the nuisance of constantly picking up the surface and laying on new materials. The iron of which the cubes are cast may be of the very worst and cheapest description, and will probably not cost the third part of common castings.—J. Macneill.