« AnteriorContinuar »
too commonly recommended that porous substances be placed above the tile. If, as is universally conceded, the water rises into the tile from below, this is unnecessary. The practice of covering the joints, and even covering the whole tile, (often to the depth of a foot,) with tan-bark, turf, coarse gravel, etc., is in no wise to be commended; and, while the objections to it are not necessarily very grave in all cases, it always introduces an element of insecurity, and it is a waste of money, if nothing worse.
The tile layer need not concern himself with the question of affording entrance room for the water. Let him, so far as the rude materials at hand will allow, make the joints perfectly tight, and when the water comes, it will find ample flaws in his work, and he will have been a good workman if it do not find room to flow in a current, carrying particles of dirt with it, unless muslin is used.
In ditches in which water is running at the time of laying the tiles, the process should follow closely after the grading, and the stream may even be dammed back, section after section, (a plugged tile being placed under the dam, to be afterwards replaced by a free one,) and graded, laid and covered before the water breaks in. There is one satisfaction in this kind of work,—that, while it is difficult to lay the drain so thoroughly well as in a dry ditch, the amount of water is sufficient to overcome any slight ten dency to obstruction.
Connections.—As has been before stated, lateral drains should always enter at the top of the main. Even in the mobt shallow work, the slightly decreased depth of the lateral, which this arrangement requires, is well compen sated for by the free outlet which it secures. (See Chap. 12.)
After the tile of the main, which is to receive a side drain, has been fitted to its place, and the point of junction marked, it should be taken up and perforated; then the end of the tile of the lateral should be so trimmed as to fit the hole as accurately as may be, the large tile re> pla e l i i its position, and the small one laid on it,— reaching over to the floor of the lateral ditch. Then connect it wiih the lateral as previously laid, fill up solidly (he space under the tile which reaches over to the top uf the main, (so that it cannot become disturbed in filling,) and lay bits of tile, or other suitable covering, around the connecting joint.*
When the main drain is laid with collars, it should be so arranged that, by substituting a full tile in the place of the collar, — leaving, within it, a space between the smaller pipes, — a connection can be made with this larger tile, as is represented in Figures 33 and 34.
Silt Basins.}—should be used at all points where a drain, after running for any considerable distance at a certain rate of fall, changes to a less rapid fall,—unless, indeed,
the diminished fall be still sufficiently great for the removal of silty matters, (say two feet or more in a hundred). They may be made in any manner which will secure a stoppage of the direct current, and afford room below the floor of the tile for the deposit of the silt which the water has carried in suspension; and they may be of any suitable material; —even a sound flour barrel will serve a pretty good
♦When such covering ia used, it is well to cover them with a mortar of wet Clay, to kei-p them in place until the ditches are tilled. tSee a note on Silt-basins at the end of this chapter.
purpose for many years. The most complete form of basin is that represented in Figure 24.
When the object is only to afford room for the collection of the silt of a considerable length of drain, and it is not thought worth while to keep open a communication with the surface, for purposes of inspection, a square box of brick work, (Fig. 35,) having a depth of one and a half or two feet below the floor of the drain,— tiles for the drains being built in the walls, and the top covered with a broad stone, — will answer very well.
A good sort of basin, to reach to the surface of the ground, may be made of large, vitrified drain pipes,—such as are used for town sewerage,—having a diameter of from six to twelve inches, according to the requirements of the work. This basin is shown in Figure 36.
Figure 37 represents a basin made of a 6-inch tile, — similar to that described on page 130, for turning a short corner. A larger basin of the same size, cheaper than if built
of brick, may be made by using a large vitrified drain pipe in the place of the one shown in the cut. These vitrified pipes may be perforated in the maimer described for the common tile.
In laying the main line (7, (Fig. 21,) an underground basin of brick work, (Fig. 35,) or its equivalent, should be placed at stake 7, because at that point the water, which has been flowing on an inclination of 1.09, 2.00 and 2.83 per 100, Fig. 37.—Tile Silt- continues its course over the much less Basin. fan of only 0.56 per 100.
If, among the tiles which have passed the inspection, there are some which, from over burning, are smaller than the average, they should be laid at the upper ends of the laterals. The cardinal rule of the tile layer should be never to have a single tile in the finished drain of smaller size, of more irregular shape, or less perfectly laid, than any tile above it. If there is to be any difference in the quality of the drain, at different points, let it grow better as it approaches the outlet and has a greater length above depending upon its action.
Covering the Tiles, and Filling-in the Ditches.—The
best material for covering the tiles is that which will the most completely surround them, so as to hold them in their places; will be the least likely to have passages for the flow of streams of water into the joints, and will afford the least silt to obstruct the drain. Clay is the best of all available materials, because it is of the most uniform character throughout its mass, and may be most perfectly compacted around the tiles. As has been before stated, all matters which are subject to decay are objectionable, because they will furnish fine matters to enter the joints, and by their decrease of bulk, may leave openings in the earth through which streams of muddy water may find their way into the tiles. Gravel is bad, and will remain bad until its spaces are filled with fine dirt deposited by water, which, leaving only a part of its impurities here, carries the rest into the drain. A gravelly loam, free from roots or other organic matter, if it is strong enough to be worked into a ball when wet, will answer a very good purpose. Fine sand is also good.
Ordinarily, the earth which was thrown out from the bottom of the ditch, and which now lies at' the top of the dirt heap, is the best to be returned about the tiles, being first freed from any stones it may contain which are large enough to break or disturb the tiles in falling on to them.
If the bottom of the ditch consists of quicksand or other silty matters, clay or some other suitable earth should be sought in that which was excavated from a less depth, or should be brought from another place. A thin layer of this having been placed in the bottom of the ditch when grading, a slight covering of the same about the tiles will so encase them as to prevent the entrance of the more "slippy" soil.
The first covering of fine earth, free from stones and clods, should be sprinkled gently over the tiles, no full shovelfuls being thrown on to them until they are covered at least six inches deep. When the filling has reached a hight of from fifteen to twenty inches, the men may get into the ditch and tramp it down evenly and regularly, not treading too hard in any one place at first. When thus lightly compacted about the tile, so that any further pressure cannot displace them, the filling should be repeatedly rammed, (the more the better,) by two men standing astride the ditch, facing each other, and working a maul, such as is shown in Figure 38, and which may weigh from 80 to 100 pounds.
Those to whom this recommendation is new, will, doubtless, think it unwise. The only reply to their objection must be that others who shared their opinion, have, bj