Imágenes de páginas
PDF
EPUB

folk, by Mr. Charles Lawrence, the owner of the estate. The earliest of which we had experience were of large area and of weak form. Constant failures resulted from their use, and the cause was investigated ; many of the tiles were found to be choked up with clay, and many to be broken longitudinally througb the crown. For the first evil, two remedies were adopted; a sole of slate, of wood, or of its own material, was sometimes placed under the tile, but the more usual practice was to form them with club-feet. To meet the case of longitudinal fracture, the tiles were reduced in size, and very much thickened in proportion to their area. The first of these remedies was founded on an entirely mistaken, and the second on no conception at all of the cause of the evil to which they were respectively applied. The idea was, that this tile, standing on narrow feet, and pressed by the weight of the refilled soil, sank into the floor of the drain; whereas, in fact, the floor of the drain rose into the . tile. Any one at all conversant with collieries is aware that when a strait work (wbicb is a small subterranean tunnel six feet high and four feet wide or thereabouts) is driven in coal, the rising of the floor is a more usual and far more inconvenient occurrence than the falling of the roof: the weight of the two sides squeezes up the floor. We have seen it formed into a very decided arch without fracture. Exactly a similar operation takes place in the drain. No one had till recently dreamed of orming a tile drain, the bottom of which a man was not to approach personally within twenty inches or two feet. To no one had it then oc. curred that width at the bottom of the drain was a great evil. For the converience of the operator the drain was formed with nearly perpendicular sides, of a width in which he could stand and work conveniently, shovel the bottom level with his ordinary spade, and lay the tiles by his hand; the result was a drain with nearly perpendicular sides, and a wide bottom. No sort of clay, particularly when softened by water standing on it or running over it, could fail to rise under such circumstances; and tbe deeper the drain the greater the pressure and the more certain the rising. A horse-shoe tile, which may be a tolerably secure conduit in a drain of two feet, in one of four feet becomes an almost certain failure. As to the longitudinal fracture-not only is the tile subject to be broken by one of those slips which are so troublesome in deep draining, and to which the lightly-filled material, even when the drain is completed, offers an imperfect resistance, but the constant pressure together of the sides, even when it does not produce a fracture of the soil, catches hold of the feet of the tile, and breaks it through the crown. Consider the case of a drain formed in clay when dry, the conduit a horse-shoe tile. When the clay expands with moisture, it necessarily presses on the tile and breaks it through the crown, its weakest part.* When the Regent's

The tile has been said, by great authorities, to be broken by contraction, ander some idea that the clay envelops the tile and presses it when it contracts. That is nonsense. The contraction would liberate the tile. Drive a stake into wet clay; and when the clay is dry, observe whether it clasps the stake tighter of has released it, and you will no longer have any doubt whether expansion or cou traction breaks the tile. Shrink is a better word than contract

Park was first drained, large conduits were in fashion, and they were, made circular by placing one horse-shoe tile upon another. It would be difficult to invent a weaker conduit. On re-drainage, innumerable instances were found in which the upper tile was broken through the crown, and had dropped into the lower. Next came the form, tile and sole in one, and much reduced in size—a great advance; and when some skillful operator had laid this tile bottom upwards we were evidently on the eve of pipes. For the Atile a round pipe moulded with a flat-bottomed solid sole is now generally substituted, and is an improvement; but is not equal to pipes and collars, nor generally cheaper than they are.” .

One chief objection to the Sole-tiles is, that, in the drying which they undergo, preparatory to the burning, the

upper side is contracted, by the more rapid drying, and

they often require to be trimFig. 14.-SOLE TILE.

med off with a hatchet before they will form even tolerable joints; another is, that they cannot be laid with collars, which form a joint so perfect and so secure, that their use, in the smaller drains, should be considered indispensable.

The double-sole tiles, which can be laid either side up give a much better joint, but they are so heavy as to make the cost of transportation considerably croton Fig. 1.-DOUBLE-SOLE TILE. They are also open to the grave objection that they cannot be fitted with collars.

Experience, in both public and private works in this country, and the cumulative testimony of English and French engineers, have demonstrated that the only tile which it is economical to use, is the best that can be found, and that the best,-much the best—thus far invented, is the “pipe, or round tile, and collar,”—and these are unhesitatingly recommended for use in all cases. Round tiles of small sizes should not be laid without collars, as the hility to use these constitutes their chief advantage; uding them perfectly in place, preventing the rattling

and thus ger sizes is, that the joints. twice the 87

in of loose dirt in laying, and giving twice the space for the entrance of water at the joints. A chief advantage of the larger sizes is, that they may be laid on any side and thus made to fit closely. The usual sizes of these tiles are 1; inches, 24 inches, and 3 inches in interior diameter. Sections of the 24 inch make collars for the 13

Fig. 16.—ROUND TILE AND COLLAR, AND THE SAME AS LAID. inch, and sections of the 31 inch make collars for the 2 inch. The 3} inch size does not need collars, as it is easily secured in place, and is only used where the flow of water would be sufficient to wash out the slight quantity of foreign matters that might enter at the joints.

The size of tile to be used is a question of consequence. In England, 1-inch pipes are frequently used, but 1; inch* are recommended for the smallest drains. Beyond this limit, the proper size to select is, the smallest that can convey the water which will ordinarily reach it after a heavy rain. The smaller the pipe, the more concentrated the flow, and, consequently, the more thoroughly obstructions will be removed, and the occasional flushing of the pipe, when it is taxed, for a few hours, to its utmost capacity, will insure a thorough cleansing. No inconvenience can result from the fact that, on rare occasions, the drain is unable, for a short time, to discharge all the water that reaches it, and if collars are used, or if the clay be well packed about the pipes, there need be no fear of the tile being displaced by the pressure. An idea of the drying capacity of a 17-inch tile may be gained from observing its wetting capacity, by connecting a pipe of this size with

* Taking the difference of friction into consideration, 14 inch piper have fully twice the discharging capacity of 1-inch pipes.

a sufficielten dry field move all theavy rain, it in getting of

a sufficient body of water, at its surface, and discharging, over a level dry field, all the water which it will carry. A 18-inch pipe will remove all the water which would fall on an acre of land in a very heavy rain, in 24 hours,-much less time than the water would occupy in getting to the tile, in any soil which required draining; and tiles of this size are ample for the draining of two acres. In like manner, 2j-inch tile will suffice for eight, and 34-inch tile for twenty acres. The foregoing estimates are, of course, made on the supposition that only the water which falls on the land, (storm water,) is to be removed. For main drains, when greater capacity is required, two tiles may be laid, (side by side,) or in such cases the larger sizes of sole tiles may be used, being somewhat cheaper. Where the drains are laid 40 feet apart, about 1,000 tiles per acre will be required, and, in estimating the quantity of tiles of the different sizes to be purchased, reference should be had to the following figures; the first 2,000 feet of drains require a collecting drain of 2;-inch tile, which will take the water from 7,000 feet; and for the outlet of from 7,000 to 20,000 feet 3;-inch tile may be used. Collars, being more subject to breakage, should be ordered in some what larger quantities.

Of course, such guessing at what is required, which is especially uncertain if the surface of the ground is 80 irregular as to require much deviation from regular parallel lines, is obviated by the careful preparation of a plan of the work, which enables us to measure, beforehand, the length of drain requiring the different sizes of conduit and, as tiles are usually made one or two inches more than a foot long, a thousand of them will lay a thousand feet,leaving a sufficient allowance for breakage, and for such slight deviations of the lines as may be necessary to pass around those stones which are too large to remove. In very stony ground, the length of lines is often materially in creased, but in such ground, there is usually rock enough

or such accumulations of boulders in some parts, to ro duce the length of drain which it is possible to lay, at least as much as the deviations will increase it.

It is always best to make a contract for tile considerably in advance. The prices which are given in the advertisements of the makers, are those at which a single thon sand,-or even a few hundred,-can be purchased, and very considerable reductions of price may be secured on large orders. Especially is this the case if the land is so situated that the tile may be purchased at either one of two tile works,—for the prices of all are extravagantly high, and manufacturers will submit to large discounts rather than lose an important order.

It is especially recommended, in making the contract, to stipulate that every tile shall be hard-burned, and that those which will not give a clear ring when struck with a metallic instrument, shall be rejected, and the cost of their transportation borne by the maker. The tiles used in the Central Park drainage were all tested with the aid of a bit of steel which had, at one end, a cutting edge. With this instrument each tile was “sounded,” and its hardness was tested by scraping the square edge of the bore. If it did not “ring ” when struck, or if the edge was easily cut, it was rejected. From the first cargo there were many thrown out, but as soon as the maker saw that they were really inspected, he sent tile of good quality only. Care should also be taken that no over-burned tile,-such as have been melted and warped, or very much contracted in size by too great heat,-be smuggled into the count.

A little practice will enable an ordinary workman to throw out those which are imperfect, and, as a single tile which is so underdone that it will not last, or which, from over-burning, has too small an orifice, may destroy a long drain, or a whole system of drains, the inspection should be thorough.

« AnteriorContinuar »