Draining for Profit, and Draining for Health Part 5

_Horse-shoe tiles_, Fig. 13, are condemned by all modern engineers. Mr.

Gisborne disposes of them by an argument of some length, the quotation of which in these pages is probably advisable, because they form so much better conduits than stones, and to that extent have been so successfully employed, that they are still largely used in this country by "amateurs."

"We shall shock some and surprise many of our readers, when we state confidently that, in average soils, and, still more, in those which are inclined to be tender, horse shoe tiles form the weakest and most failing conduit which has ever been used for a deep drain. It is so, however; and a little thought, even if we had no experience, will tell us that it must be so. A doggrel song, quite dest.i.tute of humor, informs us that tiles of this sort were used in 1760 at Grandesburg Hall, in Suffolk, 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 through 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 (which 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 forming 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 occurred that width at the bottom of the drain was a great evil. For the convenience 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 circ.u.mstances; and the deeper the drain the greater the pressure and the more certain the rising. A horse-shoe tile, which may be a tolerable 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.(9) When the Regent's Park was first drained, large conduits were in fas.h.i.+on, 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 D 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 D tile a round pipe moulded with a flat-bottomed solid sole is now generally subst.i.tuted, and is an improvement; but is not equal to pipes and collars, nor generally cheaper than they are."

[Ill.u.s.tration: Fig. 14 - SOLE TILE.]

Fig. 14 - SOLE TILE.

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 trimmed 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.

[Ill.u.s.tration: Fig. 15 - DOUBLE-SOLE TILE.]

Fig. 15 - DOUBLE-SOLE TILE.

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 transporation considerably greater. 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 c.u.mulative 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 ability to use these const.i.tutes their chief advantage; holding them perfectly in place, preventing the rattling in of loose dirt in laying, and giving twice the s.p.a.ce 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 1-1/4 inches, 2-1/4 inches, and 3-1/2 inches in interior diameter. Sections of the 2-1/4 inch make collars for the 1-1/4 inch, and sections of the 3-1/2 inch make collars for the 2-1/4 inch. The 3-1/2 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 quant.i.ty of foreign matters that might enter at the joints.

[Ill.u.s.tration: Fig. 16 - ROUND TILE AND COLLAR, AND THE SAME AS LAID.]

Fig. 16 - ROUND TILE AND COLLAR, AND THE SAME AS LAID.

*The size of tile* to be used is a question of consequence. In England, 1-inch pipes are frequently used, but 1-1/4 inch(10) 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 flus.h.i.+ng 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 1-1/4-inch tile may be gained from observing its _wetting_ capacity, by connecting a pipe of this size with a sufficient body of water, at its surface, and discharging, over a level dry field, all the water which it will carry. A 1-1/4-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, 2-1/2-inch tile will suffice for eight, and 3-1/2-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 quant.i.ty 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 2-1/4-inch tile, which will take the water from 7,000 feet; and for the outlet of from 7,000 to 20,000 feet 3-1/2-inch tile may be used. Collars, being more subject to breakage, should be ordered in somewhat larger quant.i.ties.

Of course, such guessing at what is required, which is especially uncertain if the surface of the ground is so 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 pa.s.s around those stones which are too large to remove. In very stony ground, the length of lines is often materially increased, but in such ground, there is usually rock enough or such acc.u.mulations of boulders in some parts, to reduce 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 advertis.e.m.e.nts of the makers, are those at which a single thousand,-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 sc.r.a.ping 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.

The collars should be examined with equal care. Concerning the use of these, Gisborne says:

"To one advantage which is derived from the use of collars we have not yet adverted-the increased facility with which free water existing in the soil can find entrance into the conduit. The collar for a 1-1/2-inch pipe has a circ.u.mference of three inches. The whole s.p.a.ce between the collar and the pipe on each side of the collar is open, and affords no resistance to the entrance of water; while at the same time the superinc.u.mbent arch of the collar protects the junction of two pipes from the intrusion of particles of soil. We confess to some original misgivings that a pipe resting only on an inch at each end, and lying hollow, might prove weak and liable to fracture by weight pressing on it from above; but the fear was illusory.

Small particles of soil trickle down the sides of every drain, and the first flow of water will deposit them in the vacant s.p.a.ce between the two collars. The bottom, if at all soft, will also swell up into any vacancy.

Practically, if you reopen a drain well laid with pipes and collars, you will find them reposing in a beautiful nidus, which, when they are carefully removed, looks exactly as if it had been moulded for them."

The cost of collars should not be considered an objection to their use; because, without collars it would not be safe, (as it is difficult to make the orifices of two pieces come exactly opposite to each other,) to use less than 2-inch tiles, while, with collars, 1-1/4-inch are sufficient for the same use, and, including the cost of collars, are hardly more expensive.

It is usual, in all works on agricultural drainage, to insert tables and formulae for the guidance of those who are to determine the size of tile required to discharge the water of a certain area. The practice is not adopted here, for the reason that all such tables are without practical value. The smoothness and uniformity of the bore; the rate of fall; the depth of the drain, and consequent "head," or pressure, of the water; the different effects of different soils in r.e.t.a.r.ding the flow of the water to the drain; the different degrees to which angles in the line of tile affect the flow; the degree of acceleration of the flow which is caused by greater or less additions to the stream at the junction of branch drains; and other considerations, arising at every step of the calculation, render it impossible to apply delicate mathematical rules to work which is, at best, rude and unmathematical in the extreme. In sewerage, and the water supply of towns, such tables are useful,-though, even in the most perfect of these operations, engineers always make large allowances for circ.u.mstances whose influence cannot be exactly measured,-but in land drainage, the ordinary rules of hydraulics have to be considered in so many different bearings, that the computations of the books are not at all reliable. For instance, Messrs. Shedd & Edson, of Boston, have prepared a series of tables, based on Smeaton's experiments, for the different sizes of tile, laid at different inclinations, in which they state that 1-1/2-inch tile, laid with a fall of one foot in a length of one hundred feet, will discharge 12,054.81 gallons of water in 24 hours. This is equal to a rain-fall of over 350 inches per year on an acre of land. As the average annual rain-fall in the United States is about 40 inches, at least one-half of which is removed by evaporation, it would follow, from this table, that a 1-1/2-inch pipe, with the above named fall, would serve for the drainage of about 17 acres. But the calculation is again disturbed by the fact that the rain-fall is not evenly distributed over all the days of the year,-as much as six inches having been known to fall in a single 24 hours, (amounting to about 150,000 gallons per acre,) and the removal of this water in a single day would require a tile nearly five inches in diameter, laid at the given fall, or a 3-inch tile laid at a fall of more than 7-1/2 feet in 100 feet. But, again, so much water could not reach a drain four feet from the surface, in so short a time, and the time required would depend very much on the character of the soil. Obviously, then, these tables are worthless for our purpose. Experience has fully shown that the sizes which are recommended below are ample for practical purposes, and probably the areas to be drained by the given sizes might be greatly increased, especially with reference to such soils as do not allow water to percolate very freely through them.

In connection with this subject, attention is called to the following extract from the Author's Report on the Drainage, which accompanies the "Third Annual Report of the Board of Commissioners of the Central Park:"

"In order to test the efficiency of the system of drainage employed on the Park, I have caused daily observations to be taken of the amount of water discharged from the princ.i.p.al drain of 'the Green,' and have compared it with the amount of rain-fall. A portion of the record of those observations is herewith presented.

"In the column headed 'Rain-Fall,' the amount of water falling on one acre during the entire storm, is given in gallons. This is computed from the record of a rain-gauge kept on the Park.

"Under the head of 'Discharge,' the number of gallons of water drained from one acre during 24 hours is given. This is computed from observations taken, once a day or oftener, and supposes the discharge during the entire day to be the same as at the time of taking the observations. It is, consequently, but approximately correct:

Date. Hour. Rain-fall. Discharge. Remarks.

July 13. 10 a.m. 49,916 184 galls. Ground dry.

galls. No rain since 3d inst.; 2 inches rain fell between 5.15 and 5.45 p.m.

and 1-5th of an inch between 5.45 and 7.15.

July 14. 6-1/2 " 4,968 "

July 15. 6-1/2 " 1,325 "

July 16. 8 " 1,104 "

July 16. 6 p.m. 33,398 " 7,764 " Ground saturated at a depth of 2 feet when this rain commenced.

July 17. 4,319 "

July 18. 9 a.m. 2,208 "

July 19. 7 " 1,325 "

July 20. 6-1/2 " 993 "

July 21. 11 " 662 "

July 22. 6-1/2 " 560 "

July 23. 10 " 1,698 " 515 " This slight rain only affected the ratio of decrease.

July 24. 7 " 442 "

Nothing worthy of note until Aug. 3.

Aug. 3. 6-1/2 " 8,490 " 191 " Rain from 3 p.m. to 3.30 p.m.

Aug. 4. 6-1/2 " 13,018 " 184 " " 4.45 p.m. to 12 m.n.

Aug. 5. 6-1/2 " 45,288 " 368 " " 12 m.

to 6 p.m.

Aug. 5. 6 p.m. 8,280 "

Aug. 6. 9 a.m. 3,954 "

Aug. 7. 9 " 2,208 "

Aug. 8. 6-1/2 " 828 "

Aug. 9. 6-1/2 " 662 "

Aug. 12. 6-1/2 " 368 " Rain 12 m.

Aug. 12 to 7 a.m. Aug.

13.

Aug. 13. 7 " 19,244 " 1,104 "

Aug. 14. 9 " 736 "

Aug. 24. 9 " 1,132 " 191 " " 3 a.m.

to 4.15 a.m.

Aug. 25. 9 " 5,547 " 9,936 " " 3.30 p.m. 24th, to 7 a.m.

25th.

Aug. 25. 7 p.m. 566 " 7,740 " " 7 a.m.

to 12 m.

Aug. 26. 6-1/2 a.m. 3,974 "

Aug. 26. 6 p.m. 2,208 "

Aug. 27. 6-1/2 a.m. 566 " 1,529 " " 4 p.m.