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the edge to prevent its weight from increasing the
The manner of opening the ditches, which is described above, for the main A and its laterals, will apply to the drains of the - - whole field and to all Fig 27.-BRACING THE ". . SIDES IN SOFT LAND. similar work.
Grading the Bottoms. The next step in the work is to grade the bottoms of the ditches, so as to afford a bed for the tiles on the exact lines which are indicated by the figures marked on the different stakes.
The manner in which this is to be done may be illustrated by describing the work required for the line from C 10 to C 17, (Fig. 20) after it has been opened, as described above, to within 2 or 3 inches of the final depth.
A measuring rod, or square, such as is shown in Fig. 28,” is set at C 10, so that the lower side of its arm is at the mark 4.59 on the staff, (or at a little less than 4.6 if it is divided only into feet and tenths.) and is held upright in the ditch, with its arm directly over the grade stake. The
tendency; and the sides of the ditch may be supported by bits of board braced apart as is shown in Fig. 27.
earth below it is removed, little by little, until it will touch the top of the stake and the bottom of the ditch at the
* The foot of the measuring rod should be shod with iron to prevent
its being worn to less than the proper length.
same time. If the ground is soft, it should be cut out until a flat stone, a block of wood, or a piece of tile, or of brick, sunk in the bottom, will have its surface at the exact point of measurement. This point is the bottom of the ditch on which the collar of the tile is to lie at that stake. In the same manner the depth is fixed at C 11 (4.19, ) and C 12 (4.41) as the rate of fall changes at each CWof these points, and at C15 (3.89.) and C. 17 —l (4.17,) because (although the fall is uniform from C 12 to C17) the distance is too great for accurate sighting.
Having provided boming-rods, which are strips of board 7 feet long, having horizontal cross pieces at their upper ends, (see Fig. 29) set these perpendicularly on the spots which have been found by measurement to be at the correct depth opposite stakes 10, 11, 12, 15, and 17, and fasten each in its place by wedging it between two strips of board laid across the ditch, so as to clasp it, securing these in their places by laying stones or earth upon their ends.
As these boning-rods are all exactly 7 feet | long, of course, a line sighted across their tops will be exactly 7 feet higher, at all Fig. 29.-Bonpoints, than the required grade of the ditch iNg Rod. directly beneath it, and if a plumb rod, (similar to the boning-rod, but provided with a line and plummet.) be set perpendicularly on any point of the bottom of the drain, the relation of its cross piece to the line of sight across the tops of the boming-rods will show whether the bottom of the ditch at that point is too high, or too low, or just right. The manner of sighting over two boningrods and an intermediate plumb-rod, is shown in Fig. 31.
Three persons are required to finish the bottom of the
ditch; one to sight across the tops of the boning-rods, one to hold the plumb-rod at different points as the finishing progresses, and one in the ditch, (see Fig. 30,) provided with the finishing spade and scoop, -and, in hard ground, with a pick,--to cut down or fill up as the first man calls
be beaten sufficiently hard with the back of the scoop, but if several inches should be required, it should be well
rammed with the top of a pick, or other suitable instrument, as any subsequent settling would disarrange the fall. As the lateral drains are to be laid first, they should be the first graded, and as they are arranged to discharge into the tops of the mains, their water will still flow off, although the main ditches are not yet reduced to their final depth. After the laterals are laid and filled in, the main should be graded, commencing at the upper end; the tiles being laid and covered as fast as the bottom is made ready, so that it may not be disturbed by the water of which the main carries so much more than the laterals.
Tile-Laying.—Gisborne says: “It would be scarcely “more absurd to set a common blacksmith to eye needles “than to employ a common laborer to-lay pipes and col“lars.” The work comes under the head of skilled labor, and, while no very great exercise of judgment is required in its performance, the little that is required is imperatively necessary, and the details of the work should be deftly done. The whole previous outlay,+the survey and staking of the field, the purchase of the tiles, the digging and grading of the ditches—has been undertaken that we may make the conduit of earthenware pipes which is now to be laid, and the whole may be rendered useless by a want of care and completeness in the performance of this chief operation. This subject, (in connection with that of finishing the bottoms of the ditches,) is very clearly treated in Mr. Hoskyns' charming essay,” as follows:
“It was urged by Mr. Brunel, as a justification for more ‘attention and expense in the laying of the rails of the “Great Western, than had been ever thought of upon “previously constructed lines, that all the embankments “and cuttings, and earthworks and stations, and law and “ parliamentary expenses—in fact, the whole of the out“lay encountered in the formation of a railway, had for its “main and ultimate object a perfectly smooth and level “line of rail; that to turn stingy at this point, just when “you had arrived at the great ultimatum of the whole “proceedings, viz: the iron wheel-track, was a sort of “saving which evinced a want of true preception of the “great object of all the labor that had preceded it. It “may seem curious to our experiences, in these days, tlat “such a doctrine could ever have needed to be enforced “by argument; yet no one will deem it wonderful who “has personally witnessed the unaccountable and ever new “difficulty of getting proper attention paid to the leveling “of the bottom of a drain, and the laying of the tiles in “that continuous line, where one single depression or ir“regularity, by collecting the water at that spot, year “after year, tends toward the eventual stoppage of the “whole drain, through two distinct causes, the softening “of the foundation underneath the sole, or tile flange, and “the deposit of soil inside the tile from the water collected “at the spot, and standing there after the rest had run off. “Every depression, however slight, is constantly doing “this mischief in every drain where the fall is but trifling; “and if to the two consequences above mentioned, we “may add the decomposition of the tile itself by the “action of water long stagnant within it, we may deduce “that every tile-drain laid with these imperfections in “the finishing of the bottom, has a tendency toward “obliteration, out of all reasonable proportion with “that of a well-burnt tile laid on a perfectly even inclina“tion, which, humanly speaking, may be called a perma“nent thing. An open ditch cut by the most skillful “workman, in the summer, affords the best illustration of “this underground mischief. Nothing can look smoother “and more even than the bottom, until that uncompromis“ing test of accurate levels, the water, makes its appear“ance: all on a sudden the whole scene is changed, the “eye-accredited level vanishes as if some earthquake had “taken place: here, there is a gravelly scour, along which “the stream rushes in a thousand little angry-looking rip“ples; there, it hangs and looks as dull and heavy as if it “had given up running at all, as a useless waste of energy; “in another place, a few dead leaves or sticks, or a morsel “of soil broken from the side, dams back the water for a
* “Talpa, or the Chronicles of a Clay Farm.”