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3434. A covering from four to five inches thick, according to Fry, forms a bed or mass, which is proof against the severe crush of heavy wheels, while in the case of a very thin covering, the stones lying bare upon a hard road, and receiving in this unprotected state the stroke of every wheel that passes over them, like the thin covering on a millbed, they are quickly reduced to powder, and disappear. Stones in a thick bed are protected from the immediate destructive grind; while stones that are thinly laid on are instantly reduced to powder, either by pressure

or grinding.

3435. Telford, in filling broken stones, and also in scattering them on the road, makes use of a pronged shovel, fourteen inches square, which may be universally recommended for this purpose (fig. 438 d). His large hammer (a), small one (6), and gauge for the size of the broken stone (c), are in very general use, as well as the pronged shovel. Hammers may be made

of cast iron where the stones to be broke are about their own weight; the best shape is a narrow oval; the advantage of using cast iron is its cheapness. (Farm. Mag. xxii. 159.)

438

3436. Telford's level for adjusting the declivity of roads from the middle to the sides (fig. 439.), is also a very complete implement of the kind.

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3437. The mode of depositing materials by Paterson is as follows: metals should be broken on the road. When they are thus broken, they are, by the force of the hammer, firmly bedded into the bottom, and are so closely and compactly beaten together, that they become like pavement. In this state they are not only less liable to sink, but they form a much better bed for the top metals than when they are thrown loosely on. And besides this, when they are put on in a loose manner, as is frequently done, the mud more readily works up through the metals in time of rains, and makes a disagreeable road: the top metals also are easily beaten down by the horses' feet and the carriages, through the bottom stones, when loose and open; so that the small metals frequently get undermost, and the large ones make their appearance at the surface, very much to the injury of the road. Taking all these circumstances, therefore, into consideration, it is of the greatest importance that the bottom metals should not only be much larger in size, but that they also be broken on the road." This may be considered as at variance with several parts of Paterson's second publication. (Letters, &c.) The road being drained and prepared for the materials, he then directs (p. 80.) to put them on in the following manner:-" M'Adam's mode of putting them on in coats of three or four inches, though good in particular instances, will not do as an universal rule. If the bottom is wet, and the weather rainy, the earth will poach and work up through the materials, in spite of all the attention and care that can be bestowed. I would, therefore, recommend in such cases to put on the first course from five to six inches thick. But then to leave these materials to consolidate, or rather to move and shift about by the wheels; and then to be levelled by the rakes, alternately, according to M'Adam's plan, wears away the corners of the stones, by which means they do not unite together and make such a firm road. There were upwards of two miles of road made under my directions lately, on which I caused a course of about six inches to be put. But before opening it to the public, I got a heavy stone roller to ply upon it for four days. This beat and firmed the materials so much, that the wheels of the carriages made little impression upon it. Of course the materials retained their angular points more than in rolling and shifting by every carriage-wheel that passed; and there was less labor in raking and levelling the road. This plan, which carries reason in the face of it, I would strongly recommend. As to M'Adam's plan of putting on the materials in shovelsfull, it is certainly good. I used to prohibit putting them on with carts (as in that case you never have the small and the great properly mixed together), and generally put them on with wheel-barrows. But even this does not mix them quite

so well as to scatter them with the shovel; and as it is of considerable importance to have them well mixed, I would by all means recommend the mode best calculated for that purpose."

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3438. Rolling newly laid on metals is generally approved of. The roller used should not be less than of four or five feet in diameter, a smaller size, especially in the use of gravel, being apt to drag and force the loose materials before it. Some have attempted to keep roads in order by occasionally harrowing and then rolling them; but the best judges are of opinion with John Farey, (Evidence, &c. 1819) that a roller cannot be be neficially used upon a road at any other times but after new coating it with materials, or after a frost, or when the sticking of materials to the wheels may have loosened up the

stratum.

SECT. IV. Of paved Roads.

3439. Causeways and pavements are chiefly made use of in towns, and may therefore be considered as belonging more to architecture than to agriculture. But as it is the opinion of some of the first engineers that pavements might be introduced with advantage on the public roads for some distance from the larger towns, we shall shortly consider this subject with reference to that object. Paving, as applied to roads, is therefore to be considered as a substitute for a part or the whole of the metalled part of the road, and not as occupying every part of its width or site, as in the case of streets.

3440. For roads near capital or great commercial towns, paving, according to Edgeworth, is the only certain method yet known that gives sufficient hardness, smoothness, and permanency to a road. B. and J. Farey are of the same opinion, and the latter considers it would be proper to pave the sides of all the principal entrances into London. Walker, who was the engineer of the Commercial road, ten feet of the centre of which is paved with granite, and has given great satisfaction for upwards of 16 years, is a great advocate for paving. The advantage, he says, of paving part of a road where the traffick is great, and the materials of making roads bad or expensive, is not confined to improving the conveyance for heavy goods and reducing the horses' labor; but as the paving is always preferred for heavy carriages, the sides of a road are left for light carriages, and are kept in much better repair than otherwise they could possibly be. It is not overstating the advantage of the paving, but rather otherwise, to say, that taking the year through, two horses will do more work, with the same labor to themselves, upon a paved road, than three upon a good gravelled road, if the traffick upon the gravel road is at all considerable, and if the effect of this, in point of expense, is brought into figures, the saving of the expense of carriage will be found to be very great when compared with the cost of the paving. If the annual tonnage upon the Commercial road is taken at 250,000 tons, and at the rate of only 3s. per ton from the docks, it could not upon a gravelled road be done under 4s. 6d., say however 4s., or 1s. per ton difference, making a saving of 12,500l., or nearly the whole expense of the paving in one year. The introduction of paving, therefore, would, in many cases, be productive of great advantage, by improving the gravel road, reducing the expense of repairs, and causing a saving of horses' labor much beyond what there is any idea of.

3441. Telford considers that it would be of advantage to pave a part of the centre of great public roads; and in conformity with this principle, when forming a gravel road, he lays eight or ten feet of it in the centre with stones.

3442. The part of the road most desirable to be paved, according to B. Farey, is the sides. "If the centre was paved," he says, "the light carriages would be much annoyed; when the gravel road was good on the sides, the heavy carriages would go there, and the light carriages would be driven on the stones from the sides again; if the centre was paved, the carters would be obliged to walk on that road to manage their horses, and would be considerably annoyed by carriages, horsemen, &c. passing: but if the sides of that road were paved, the carters would be enabled to walk on the foot-path, and to manage their horses without annoyance."

3443. Paving the sides is also preferred by J. Farey, "but not the middle, as has been done on the Commercial road, and Borough stones and road. My reasons for preferring the sides being paved are, that it is next to impossible to compel the carters to keep upon the pavement in the middle of the road, in too many instances; the fear of damage, from the swift going carriages, occasions them either to draw their carts close to the sides, and walk upon the footpaths, or, what is worse, to leave their horses in the middle, beyond a train of carriages. The sides being paved, would enable one of those trains of carriages to enter London on one side of the road, and go out of it on the other, without many occasions to turn out of their tracks, which circumstance of keeping nearly to the same tracks, upon a well-paved road, would not be prejudicial; but on a road formed of gravel is entirely ruinous."

3444. Walker also prefers paving the sides, though in the case of the Commercial road he paved the centre, as already described (3440.).

3445. Paving the whole or any part of a road is entirely disapproved of by M'Adam. "The measure," he says, "of substituting pavements, for convenient and useful roads, is a kind of desperate remedy, to which ignorance has bad recourse." The badness, or scarcity of materials, cannot be considered a reasonable excuse; because the same quantity of stone required for paving, is fully sufficient to make any excellent road any where : and it must be evident, that road materials of the best quality may be procured at less cost than paving stone. The very bad quality of the gravel round London, combined with want of skill and exertion, either to obviate its defects, or to procure a better material, has induced several of the small trusts, leading from that city, to have recourse to the plan of paving their roads, as far as their means will admit. Instead of applying their ample funds to obtain good materials for the roads, they have imported stone from Scotland, and have paved their roads, at an expense ten times greater than that of the excellent roads lately made on some of the adjoining trusts. Very few of these pavements have been so laid as to keep in good order for any length of time; so that a very heavy expense has been incurred without any beneficial result, and it is to be lamented that this wasteful and ineffectual mode is upon the increase in the neighborhood of London.

3446. The practice of paving roads has also been adopted in places where the same motive cannot be adduced: in Lancashire, almost all the roads are paved at an enormous cost, and are, in consequence, proverbially bad. At Edinburgh, where they have the best and cheapest materials in the kingdom, the want of science to construct good roads, has led the trustees to adopt the expedient of paving to a considerable extent; and at an expense hardly credible, when compared with what would have been the cost of roads on the best principles.

3447. The advantages of good roads, when compared with pavements, are universally acknowledged; the extension of pavement is therefore to be deprecated as an actual evil, besides the greatness of the expense. Pavements are particularly inconvenient and dangerous on steep ascents, such as the ascent to bridges, &c. A very striking example of this may be observed on the London end of Blackfriars bridge, where heavy loads are drawn up with great difficulty, and where more horses fall and receive injury than in any other place in the kingdom. The pavement in such places should be lifted, and converted into a good road, which may be done with the same stone at an expense not exceeding 10d. per square yard. This road would be more lasting than the pavement, and, when out of order, may be repaired at less than one-tenth of the expense which relaying the pavement would require. This measure has been adopted with great success, and considerable saving of expense, in the suburbs of Bristol, where the pavements were taken up, and converted into good roads, about three years ago. The same thing has lately been successfully adopted on Westminster and Blackfriars bridges.

3448. In preparing for laying down pavements, the first thing, Edgeworth observes, to be attended to is the foundation. This must be made of strong and uniform materials, well rammed together, and accurately formed to correspond with the figure of the superincumbent pavement. This has no where been more effectually accomplished, than in some late pavement in Dublin. Major Taylor, who is at the head of the paving board, before he began to pave a street, first made it a good gravel-road, and left it to be beaten down by carriages for several months; it then became a fit foundation for a good pavement. The Romans, in preparing for pavement, laid a substratum of masonry in some cases two or more feet thick, and never less than a foot or eighteen inches. This mode is adopted in one or two cases near St. Petersburgh, and might be advantageously used in this country were not the expense an objection. Planking, broad stones, iron plates, slates, tiles, and brick work has also been proposed in this country; but a consolidated stratum of broken stone of ten inches in thickness is perhaps the simplest and best preparation, especially for the sides of roads. A substratum of sand is sure to be deranged after the first rains.

3449. The kinds of stone used in paving are chiefly granite, whinstone or trap, Guernsey or other pebbles, or water worn granitic or trapstones. Walker prefers the granite of Guernsey to that of Aberdeen.

3450. The size of the stones used in road pavements is commonly from five to seven inches long, from four to six inches broad, and from six to eight inches deep. Walker prefers stones nine inches deep; and Telford is of opinion that the general shape of the stones at present used for paving, and the modes of distributing them, are very imperfect, the lower part of the stones being of a triangular wedge-like shape, which, instead of enabling them to resist the weights which come upon them, easily penetrate into the substratum; the stones are also broken of an unequal size. The remedies for these defects are obvious; they should be as nearly as possible of a cubical form, the lower bed having an equal surface with the upper face; they should be selected as nearly as possible of an equal size, and they should never be of equal length on the face. In quarrying and preparing the stones there would certainly be an additional expense in the preparation, because there would be more work required in the dressing, and many stones must

be rejected which are now used; but the additional expense would be very well bestowed.

3451. In laying down the stones, each stone, according to Edgeworth, should bear broadly and firmly on its base; and the whole should be rammed repeatedly, to make the joints close; the upper and lower sides of the stones should be as near each other as possible, but they should not touch each other laterally, except near the top and bottom, leaving a hollow in the middle of their depth, to receive gravel, which will serve to hold them together. This method of paving may be easily executed by common workmen, who may throw in gravel between the stones as they are laid down. It may be easily conceived, that if a grain of gravel inserts into holes that are in stones opposite to each other, they will dowel them together. It will be useful to cover a newly-made pavement with gravel, which will preserve the fresh pavement for some time, from the irregular pressure of wheels, till the whole is consolidated. It should be observed, that the stones should be of equal hardness, or the soft ones will be worn down into hollows. In every species of paving no stones should be left higher or lower than the rest; for a wheel descending from a higher stone will, by repeated blows, sink or break the lower stone upon which it falls.

3452. The requisites for laying down the stones and forming a good pavement are, according to Walker, to have the stones properly squared and shaped, not as wedges, but merely as rectangular prisms; to sort them into classes according to their sizes, so as to prevent unequal sinking, which is always the effect of stones, or rows of stones, of unequal sizes being mixed together; to have a foundation properly consolidated before the road is begun to be paved; to have the stones laid with a close joint, the courses being kept at right angles from the direction of the sides, and in perfectly straight lines; the joints carefully broken, that is, so that the joint between two stones in any one course shall not be in a line with or opposite to a joint in any of the two courses adjoining. After the stones are laid they are to be well rammed, and such of the stones as appear to ram loose, should be taken out and replaced by others; after this the joints are to be filled with fine gravel, and if it can be done conveniently, the stability of the work will be increased by well watering at night the part that has been done during the day, and ramming it over again next morning. The surface of the pavement is then to be covered with an inch or so of fine gravel, that the joints may be always kept full, and that the wheels may not come in contact with the stones while they are at all loose in their places. Attention to these points will very much increase both the smoothness and the durability of the paving. He has found great advantage from filling up, or, as it is called, grouting the joints with lime-water, which finds its way into the gravel between and under the stones, and forms the whole into a solid concreted mass. The purpose served by the lime might also be effectually answered by mixing a little of the borings or chippings of iron or small scraps of iron hoop, with the gravel used in filling up the joints of the paving. The water would very soon create an oxide of iron, and form the gravel into a species of rock. He has seen a piece of rusty hoop taken from under water, to which the gravel had so connected itself, for four or five inches round the hoop, as not to be separated without a smart blow of a hammer; and the cast-iron pipes which are laid in moist gravel soon exhibit the same tendency.

3453. As substitutes for paving stones, plates of cast iron moulded into the form of the surface of a pavement of different sizes, (fig. 442 c, d, e), have been tried; but on the whole they are not considered as likely to succeed. They are very hot in summer and more slippery than stone in winter; but what is most against them is, that the water finds its way beneath them and softens the substratum. This, at any time of the year, tends directly to produce holes by the leverage of the wheels and feet of animals ($325.); but after a severe frost the effects are ruinous. At all events this description of pavement does not appear so well adapted for the sides or middle of public roads as that of granite stones prepared in Telford's manner (3450.).

440

3454. Various improvements in laying pavements have recently been devised, such as laying the stones dry on clay, using square stones, or stones equally wide at bottom as at top, using stones alternately wider at bottom and top, and joining them with cement (fig. 440.), paving on plates of iron, wood or stone, or on a mass of masonry, &c. pavements in towns did not require to be frequently lifted

If

on account of sewers, and water and gas pipes, paving indultad this manner on a solid foundation would certainly be the

best mode; but as things are, and even probably if pavements did not require to be frequently lifted, M'Adam's roads are found greatly preferable for all broad streets, and where attention is had to keep them clean and in complete repair. In Britain at least, they will probably soon supersede all common pavements, and all other description of common roads.

441

3455. Large blocks of granite (fig. 441.) have been substituted for common-sized paving stones; each block is two or more feet square, nine inches deep, and channelled on the surface in imitation of common-sized paving stones. These are found to answer much better than the cast iron plates; but they are liable to the same objection as to leverage; are difficult to replace properly; and as the raised pannels between the grooves will in time wear down to the level of the grooves, they cannot be considered so durable as common square stones; which after all appear the best for general purposes, and at all events for paving the middle or sides of highways. 3456. The defects of common pavement and the theory of its wear, are thus given by Edgeworth. "Stones, in a common pavement, are usually somewhat oval, from five to seven inches long, and from four to six inches broad. They are laid in parallel rows on the road (fig. 442 c, d), or alternately (a, b), as bricks are laid in a wall. On the first sort of pavement wheels slip from the round tops of the stones into the joints between, and soon wear away the edges of the stones, and their own iron tire. By degrees, channels are thus formed between some of the stones, and in time the pavement is ruined.

442

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3457. On the second sort of pavement (a, b), where the stones are placed alternately, to prevent the injury to which the former method is liable, the wheel (f) sliding sideways, makes a channel between two stones, and is then obliged to mount from the groove which it has made, to the top of the stone opposite to it; when it has attained this situation, the wheel may slide sideways, or may go forward over the top of the stone, till it drops into the interstice between the two next stones. By continual wearing, these ruts become so wide and deep, that the wheel does not touch the stones on either side, nor does it reach the ground between them, but it bounds from one stone to the other, thus jolting the carriage in every direction. This method is not at present in use.

3458. In the pavements hitherto described, the stones are but of a small size; but if flat stones of twelve or fourteen inches long (e) are well laid, wheels are not liable to slide into the joints; and if such stones are laid with their longest sides crossing the road they are less liable to injury; but still narrow wheels sometimes fall into the joints between the largest stones, and having in time worn away their own edges, and those of the stones, they will act like wedges, and will displace the stones. No pavement, of the best stone that could be procured, can long resist this action of a narrow wheel. the only effectual means of preserving pavement is, to increase the breadth of all wheels to at least three inches. Were no wheels narrower, a cheap and durable pavement might be made of flat stones, not more than three inches square, provided they were eight or nine inches deep, to give them reciprocally lateral support; for the tire of such broad wheels could never sink between the joints of the stones. (Edgeworth.)

SECT. V. Of Railroads.

And

3459. Railways or tramroads are not intended to be considered here as connected with mines, canals, or other works which come directly under the province of the higher branches of engineering; but merely as substitutes for the whole or a part of the metalled surface of common roads. The necessity of an expeditious and cheap mode of conveying coals from the pits to the ships, had, as early as the year 1680, introduced the use of wooden railways, for the waggons to move upon, between the Tyne river and some of the principal pits, and these by degrees became extended to a great number of other coal-works. They were first solely employed for transporting coals to a moderate distance from the pits, to the places where they could be shipped, being universally made of wood. By degrees they were, however, carried to a farther extent; the scarcity of wood, and the expense of their repairs, suggested the idea of employing iron for the purposes of improving these roads. At the first, flat roads of bar-iron were nailed upon the original wooden rails, or as they were technically called, sleepers; and this, though an expensive process, was found to be a great improvement. But the wood on which these rested being liable to rot and give way, some imperfect attempts were made to make them of cast iron, but these were found to be liable to many objections, until the business was taken in hand by Outram, an engineer at Butterly Hall, Derbyshire, who contrived at the same time, so far to diminish the expense, and improve the strength of the road, as to bring them to a degree of perfection, that no one who has not seen them can easily conceive could have been done. This having been carried into execution in a few cases, and found to answer, has been improved upon and simplified by practice, till it is now brought to such a state of perfection as to have

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