Page:The Building News and Engineering Journal, Volume 22, 1872.djvu/528

 506 THE BUILDING NEWS. June 21, 1873. eee sewers have been laid in headings systemati- cally in the not too much frequented thorough- fares of a town at a depth of no more than 10ft. or 15ft. ‘The consequences have shown themselves in such accidents as we have men- tioned, within a few years of the sewers having been laid. In connecting the house-drains with the public sewers, where the drains must pass under the footways, even in towns of com- paratively small traflic, it may be well to drive short headings under them, as well as to drive short headings for the main sewers underthe crossings of public streets. A few of these we can mention. In the case of a sewer 2ft. Gin. wide, and 3ft. 9in. high in the clear, the brickwork being Qin. thick, short headings of 12ft., and of 15ft., were driven in sandy gravel at a cost of 2s. Gd. per lineal yard. The depths at the various places were from 10ft. to 16ft. from the surface to the invert. There was no water. The headings for sewers ft. wide, and 3ft. high in the clear, the thickness of brickwork being also Qin., cost 2s. 1d. per lineal yard. In connecting the house drainage with these sewers by means of 6in. pipes, the hole was 3ft. x 2ft., and the cost was 1s. 6d. per lineal yard for such short lengths as were driven from the sewers to the cellars of the houses, which did not, in general, exceed 8 yards. This cost was that of excavating, laying the pipes with clay joints, and filling in again; ‘“ laying” includ- ing the labour of lowering and carrying the pipes. ‘The trench of the sewer first-named —yviz., that which was of the internal dimen- sions of 3ft. Yin. by 2ft. 6in., was 4ft. wide, and varied from 10ft. to 16ft. in depth in the town. ‘The ground is sand and sandy gravel. In the meadows, towards the outfall, the ground is clay. It is not easy to estimate with accuracy the value of sewer excavations ; so many contin- gencies are often met with. There may be water where none could haye been expected, or a very large quantity where only a mode- rate quantity could be anticipated; veins of running sand; beds of rock in ground that might be supposed to be all clay, &c. By practice—and plenty of it—one may know certain facts which may afford a tolerably sure basis upon which to form an opinion, but the only thing which can be stated in general terms is the actual value of a simple ease as a standard, or minimum, and to add to it whatever the requirements of any particular case seem to demand. Basing this minimum on experience, the following results are arrived at for sewer and pipe trenches in open cutting in good ground—the best. In ground that requires no getting—if any one should be inclined to say that all ground must be got before it can be removed, it may be well to remind him that in earth- work the term geiting is restricted to the use of the pick. Earth that is removed without the use of the pick is dug, and rock that is too hard to be got with the pick or with hammers and wedges is blasted. Earth that requires no getting is worth 34d. per cubic yard to cast on to stages the extreme height of which is not more than 6ft. (speaking of sewer trenches, the progress of the excavation of which is vertically downwards, the mean lift of each stage being, therefore, 3ft.) The top soil is worth 4d. per cubic yard to dig, fill into barrows, and wheel to a distance not exceeding 20 yards. It is worth rather more in trench work than in stripping a broad area, on account of the barrow roads having to be more often shifted for the same quantity of soil removed. ‘The second foot in depth is worth 4d. per cubic yard to dig and cast to a horizontal distance of 12ft. The next foot in depth, which makes the third from the top, is worth the same price to dig and cast to a horizontal distance of 9ft. The fourth foot, 4d., to dig and cast to a horizontal distance of 6ft. The fifth foot is worth 4d. to dig and cast on top, and 2d. to cast it again into heap, which makes the fifth foot worth 6d. percubie yard. The sixth foot is worth 5d. to cast up on top, and 24d. to cast into heap, making 74d. And now stages are put in, for it is too high to cast up the earth from a further depth. During the time the depth has been progressing to 6ft., one set of timbering will have been put in at about 2ft. below the top. On the struts of this set of timbering stages of short planks are to be made. The timbering of trenches consists in shor- ing up the ground from side to side by fixing up, horizontally, deals or planks, Sin. thick, opposite each other, and driving in between them struts cut at a length a little longer than the width measured between the two planks. This width is best measured with two sticks or square rods of wood, each of them about 6in. longer than half the width between the planks. These, being placed side by side, are slid out- wards until the end of each touches its plank, and, being gripped firmly by one of the timbermen, is carried to a strut andthe length marked off upon it, about an inch longer than the measured width, to allow for driving. The strut then being placed aslant between the planks is driven until it stands square across the trench, by which means the planks are tightened against the sides, and the struts will carry a considerable weight by their friction against the planks. ‘The most convenient length of plank is 14ft. A strut being then driven at 1ft. from each end, and another in the middle, they stand 6ft. apart. The stage- planks being then cut 6ft. long, or a little longer, they lie upon the struts. The struts are sometimes cut 4in. square, but are often of round sticks of fir 5in. to Gin. diameter. The top stage being on the first set of timber- ing will be about 2ft. below the surface of the ground. On to this stage the earth is to be cast from the depth last mentioned—yviz., 6ft., down to a depth of 6ft. again below the stage, which will be down to a depth of Sft. from the surface. At this depth it will generally be necessary for safety to put in another set of timbers—that is to say, at 7ft. below the sur- face, if the trench is to be continued much further down. The top stage being now out of reach a second stage is put in, not directly under the upper one, but upon the alternate pair of struts. Upon this second stage the earth is cast from the eighth foot doyn to the fourteenth. Toresume the prices from the sixth foot, the seventh foot isworth 3d. to dig and cast itupon the top stage, 24d. to cast it on top, and 24d. to cast it into heap, making 8d. The eighth foot is worth 3$d., 24d., and 24d., making 8}d. The ninth foot is cast upon the second stage, costing 3d. per cubic yard, casting it up from the second to the top stage 3d., from the top stage to the side of the trench 23d., and into heap 24d., making 11d. The tenth foot, 3d. on to the lower stage, 3d. from the lower to the upper stage, 24d. and 24d. as before, making 11d. The eleventh foot, 54d. on to the lower stage, 3d., 24d. and 24d. as before, making 114d. The twelfth foot, 4d. on to the lower stage, 3d., 24d., and 24d. as before, making 12d. per cubic yard. The thirteenth foot, 124d., and the fourteenth, 13d. The stuff that has been thrown out is to be filled in again, and must be well rammed—or punned, as itis often called, being probably a corrupted form of the word pounded—to put it back again into the same space from which it came. One man can fill in as much as another can wellram. If the earth has stood alongside the trench in the heap into which it had been thrown it will occupy a considerable width of ground. Its nearest edge to the trench should not be nearer than 2ft., in order to leave a passage for the work- men and materials. If the width of the trench be 3ft. and the depth 10ft. the width which the heap will occupy will probably be 9ft. or LOft. ‘This makes its mean distance from the edge of the trench 7ft. It must be shifted twice ; once to the filler and once by him. A man will fill in 20 cubic yards a day. Thus, two men filling and one punning make three men to 20 yards. If the wages be 2s. 10d. a day the cost will be 5d. per cubic yard. Filling in and punning is often put down in estimates at 4d. per cubic yard, but at that price the punning must be imperfect. If the ground be sand it must be consolidated by watering instead of punning, but in most cases it will cost as much to water it as to punit. Ramming dry sand or clean gravel is useless labour. ; In pipe trenches, whether of earthenware for sewers or iron for water or gas pipes, it is important to ram the earth well down at the sides of the pipes, for which purpose small stuff is to be used. If hollows are left at the bottom there will be a continual sinking. The filling is to be done carefully in layers. When the trench has been filled with earth, the road-bed, if any—which must have been pre- viously removed separately and reserved out- side the work—is to be brought back and replaced, upon which the road metal, or paying, as the case may be—having also been carefully removed and stowed away outside the work—is to be reinstated. Sixpence per square yard wlll generally cover the cost of this. In‘like manner in fields the top soil is to be brought back, but it may be included in the estimate with the remainder of the filling in. There are other expenses, of course, be- sides these, even in the best ground. The waste, wear, and tear, and labour of timbering may be set down at 14d. per cubic yard, and. superintendence at jd. The quantity of earth displaced by the sewer will, in most cases, have to be removed; generally it is carted away to some distance, say a mile, in which case it will cost 1s. per cubic yard to fill and cart away. To take an example of the cost of open cutting a trench in good ground: take the moderate dimensions of 3ft. wide and 10ft. deep. Allowing 1ft. for the depth of the road metalling or paving, and taking that separately, as we have mentioned, there remain 9ft. depth of excavation; there would consequently be three cubic yards in a yard forward. It is to be observed that, unless the ex- cavated material be clean sand or other saleable material, the trench work costs more per cubic yard for large than for small sewers, for the stuff can be refilled into the trench at a cost of 5d. per cubic yard, but to cart it away could seldom, if ever, be done for that. Therefore, the more surplus earth to be removed, so much more must be the cost of the trench. It is not an unusual thing for the removal of surplus earth to cost 2s. or 3s. per cubic yard. To take an extreme case, it is understood that the cost of removal of the earth from the foundations of the New Law Courts in London has been 5s. per cubic yard ; but this may be a price agreed upon which shall cover risks of finding tipping places for it, in the nature of a large contract, whereas in the figures above given as the cost of work they represent the bare cost in wages, horse- hire, &e. The road metalling or paving, and the road bed, are each to be removed separately and reserved for re-use. They may be taken to be on an average afoot in depth, and to cost, for removal and replacing, 1s. per square yard. Beginning with the second foot, the cost of the excavation for any depth may be found by taking a mean of the several prices aboye given, thus, for 10ft. deep, the Per cubic yard. D. 2nd foot in depth is to be taken at the rate of.... . 8rd ” 4th 0 4 5th A & 6th ” 7s 7th “ 8 8th _ 8h 9th “ 11 10th a IL 64 Mean. .o0renceeee Come ecmesien, 7 To which add for timbering and superintendence... 2 9