METROPOLITAN STREET SURFACES.
1 Adam Street, Adelphi, 31st October 1853.
Sin—The transit between the City and the West-end of London has lately experienced such a succession of interruption that it would almost seem as though it were a purposed thing produced by forethought. Much of it, doubtless, is a result of a population grown too numerous for the thorough- fares; but much of it also is due to the imperfect mode of paving the sur- faces. The stoppage for paving has not been in the latter cases produced by the direct repairs of pipes or sewers, though indirectly it has been much ag- gravated. How to amend this evil is a question for consideration.
Under the carriage portion of the streets, at a given depth, lie the main sewers ; under the side-walks are the ranges of coal-vaults. Over the sewers, bedded in earth of greater or lesser density, lie the main water-pipes. Un- der the foot-ways and elsewhere lie the smaller water-pipes, house service- pipes, gas-pipes, and, latterly, electric telegraph pipes in some streets. The water-pipes leak occasionally, and the street is taken up to repair them. The gas-pipes leak incessantly, from faulty construction—the want of elastic joints; and, in addition to the waste of gas, a poisonous atmosphere is gene- rated. The electric telegraph must sometimes get out of order ; and in all eases the street has to be taken up% frequently one repair following another in. succession, instead of being simultaneous. And lastly, there is the re- pair of the street itself independently of the pipes and sewers.
Had the streets been rightly constructed, proper arrangements would have been provided to get access to the sewers for repairs without disturbing the surface. And vaulted passages would have been constructed beneath the sur- face in which to lay the pipes of every kind, and thus save breaking up the surface : but this appears too late to talk about in existing streets, and even in new streets it is not attended to.
After the street has been dug up for the repairs of pipes, the usual plan is to tumble back the earth into the trench, with varying solidity, or rather with no solidity atalL If by chance rain happens to fall, the permeation of water renders the mils more compact but still not solid. On this unfirm bedding the surface stones are placed dry side by side, and rammed by a one-man beetle, the weight and momentum of which bear about the same propor- tion to the weight, and momentum of a coal-waggon wheel that a French poodle bears to a, brewer's horse. This upper surface with a mock sub-sur- faceis then grouted with a liquid concrete, and it is considered a perfect specimen of modern art in paving.
But lime cement or mortar when hardened is a brittle substance ; and if the stones do not thoroughly adhere together, they settle down unequally, the cement is broken, and goes into powder or mud according as the season is dry or wet. The surface settles unevenly, and the mud rises up between the
ere.viceva,sa.r: is carried away by the scavengers; or the powder flies up and is carried awai by the wind, to the great annoyance of all passengers and shop- keepers, and a considerable loss by damaged goods.
But if the stones of the surface were considered as what they really are- a mere wearing material and not the road itself—there would be some chance of a sound principle of construction obtaining. The pavement is to the road what the tyre is to a wheel, or the sole to a shoe—a substance to be renewed when worn, if deemed desirable. It is true that the pavement serves to strengthen the road, as the tyre does the wheel ; but this is only incident- ally : an independent road is required, on which the pavement or surface may be laid, and renewed as often as worn out without disturbing the road itself.
The best kind of paving in present use as surface is composed of granite blocks, about twelve inches lon't, eight inches deep, and four inches wide. They are laid in parallel lines across the street, in an arching form, and with the joints intersected, similarly to bricks. They are, moreover, laid slightly out of the perpendicular, so that there is a vertical pressure of one in the other ; with the further advantage in one respect, that as one edge of the stone when worn to the horizontal level forms an obtuse angle and the opposite edge an acute angle' the latter is continually broken away, and forms a groove or hold for the horses' feet. But this advantage is purchased by a considerable disadvantage, inasmuch as these cross-grooves produce an incessant series of jolts to the carriage-wheels, engendering noise and de- struction, and absorbing some considerable portion of horse-power by in- creased tractive resistance.
It is obvious that the smoother and harder the surface the less will be the resistance, and that the present mode of paving is a compromise between resistance and foot-hold: and this opens up another inquiry. Are our draught-horses shod in a mode to produce the best results of traction in our streets ? The answer to this must be, that the shoeing itself is a compro- niise.
Horses used upon turf need no shoes, and a horse accustomed to be with- out shoes is as clumsy as "a cat in pattens " when they are first applied. They are applied to prevent the wear of the hoofs on rough stony roads ; and iron is used as the only durable material, upon the principle that in- duces ploughmen and others to use boots tipped and hob-nailed, while per- sons using smooth pavements are satisfied with leather. My attention was first called to this question of horses' foot-hold, by observing the effect on a favourite horse shod with iron for the first time, to cross the stony roads or rather tracks of the Andes. I judged his knees to be in peril after the first day's experience ; and the iron shoes were removed and replaced by shoes of strong raw hide, laced round the hoofs, and tightened by shrinking. It was a substance analogous to the hoof itself, and there was no more slipping. As those shoes cut on the stones, they were replaced without very much trouble, till alluvial soil was attained, when they were removed altogether. Now the best surface for traction—leaving metal out of the question— would be large slabs of granite, similar to those that cover the loot-pave- ments of London Bridge. With such a surface, less horse-power would be requisite ; and horses might be shod with leather or similar substances, and would not slip more than foot-passengers, supposing that the streets were kept constantly washed clean. At present, the slipperiness is caused by the dirt which oozes up between the joints of the stones, and the animal and vegetable matter that is triturated by the traffic. If the surface were of large slabs, there would be no dirt oozing up, and the animal and vegetable mat- ter only would require removing. And the noise of the wheels would be reduced to a mere hum, and the sound of the horses' feet nearly lost. Roads with a similar hard surface exist in Italy, and the wheel-ruts worn in them by time show clearly that foot-hold thereon for the draught cattle was no insuperable difficulty.
The wood pavement so largely used, and so unwillingly abandoned, and remembered with affection by residents in streets of traffic as a noiseless as- sistant in " letting their lodgings," failed for three reasons,—first, its too rapid abrasion by its softness ; secondly, its slipperiness by dirt and moisture ; and thirdly, by its sinkine.* unequally and forming holes.
In the stone surfaces the want of under surface is sought to be com- pensated for by interlocking the stones, and trying to make them into a solid arch, by the use of concrete, abutting against the kerb-stones on either side. But the vibrations destroy the arch, and it sinks in patches into the soft mass below. The bearing surface of each stone is about forty-eight square inches. If, therefore, the adhesion is broken between one stone and another, they can be separately driven down by the weight and concussion of the vehicles.
The plain remedy is, to make the surface in such masses that no rolling load can disturb the stones, and that no water can penetrate below, or mud ooze up between the joints. The simplest mode of accomplishing this would be, to make a level flooring of large flag-stones, on that to place a bed of concrete of hot lime, and on that to lay the stones of the wearing surface. This would be a mosaic pavement; more costly to make than the common kind, but of a durability, cleanliness, dryness, and freedom from dust and mud, that would soon repay the cost many times over ; a pavement that would not sink into holes, and which would not be subject to fracture of the concrete, and, moreover, might have its surface renewed in a much shorter space of time. But the access to the sewers and pipes has to be considered. The flagging would be an impediment to getting at them. As regards the sewers, exterior holes might easily be provided. As to the main water-pipes, they rarely require repair. The smaller water-pipes, the gas and other pipes, might be provided for by changing the structure of the side-paths. The ranges of coal-vaults beneath the side-paths are usually arched above. By the substitution of large flag-stones, or what are technically called land- ings, for these arches a depth of two feet might probably be gained below i
the exting level. 1.hese flags should be placed with a considerable hori- zontal slope towards the street, with provision for the surface-water to drain from them into the sewers. The walking surface should be frames of cast iron, lined with tile or cement for the feet, laid at a horizontal level, and perforated, so as to carry off water or mud or dust. These frames should be removeable ; and thus access would at all times be gained to the pipes in the recess below, for the purpose of repairs, and without involving any dust or trouble in replacing the pavement. In this mode, any leakage of gas would be instantly detected, and a surface free from mud or wet, and horizontally level, would afford a much better footing for the passenger.
The problem might thus be solved of getting rid of the frequent stoppages by incessant paving, and obtaining at the same time surfaces that might be washed clean as easily as slabs of slate, with an absolute riddance of mud and dust, and this without materially interfering with other existing arrange- ments. Whether a further experiment could be carried into execution, of arranging horses' feet to tread safely on smooth surfaces, is contingent on other circumstances.
The question has been thus far treated as to the possible improvement of the surface of the streets. The question of whether we have yet attained the most convenient and economical arrangements for Metropolitan transit needs a much wicks discussion. At a future time I will endeavour to indi- cate the direction which improvement should take.