CHAPTER XXI.

METHODS AND COST OF AQUEDUCT AND SEWER CONSTRUCTION. Aqueducts and sewers in concrete are of three kinds: (1) Continuous monolithic conduits, (2) conduits laid up with molded concrete blocks, and (3) conduits made up of sections of molded pipe. Block conduits and conduits of molded pipe are rare in America compared with monolithic construction; examples of each are, however, given in succeeding sections, where forms, methods of molding, etc., are described. The following discussion refers to monolithic construction alone. ~FORMS AND CENTERS.~--Forms and centers for conduit work have to meet several requirements. They have to be rigid enough not only to withstand the actual loads coming on them, but to keep from being warped by the alternate wetting and drying to which they are subjected. They have also to be constructed to give a smooth surface to the conduit. To be economical, they have to be capable of being taken down, moved ahead and re-erected quickly and easily. The carpenter costs run high in constructing conduit forms, so that each form has to be made the most of by repeated use. Three different constructions of traveling forms are described in the succeeding sections. For small work, such forms appear to offer certain advantages, but for conduits of considerable size their convenience and economy are uncertain. The experience with the large traveling form employed on the Salt River irrigation works in Arizona was, when all is said, rather discouraging. The authors believe that for work of any size where the concrete must be supported for 24 hours or more, forms of sectional construction will prove cheaper and more expeditious than any traveling form so far devised. No class of concrete work, perhaps, offer so good an opportunity for the use of metal forms as does conduit work. The smooth surface left by metal forms is particularly advantageous, and there is a material reduction in weight and a large increase in durability due, both to the lack of wear and to freedom from warping. Steel forms of the Blaw type shown by Fig. 247, have been used for conduits up to 25 ft. in diameter. The form illustrated, Fig. 247, was for a 12-ft. 3-in. sewer; in this case a roof form alone was used, but full circular and egg-shape forms are made. The Blaw collapsible Steel Centering Co., of Pittsburg, Pa., make and lease steel forms of this type. [Illustration: Fig. 247.--Blaw Collapsible Steel Centering for Conduit Construction.] Sectional wooden forms for conduits of large diameters are shown by the drawings in several of the succeeding sections. Figures 248 and 249 show such forms for small diameters. The form shown by Fig. 248 is novel in the respect that after being assembled a square timber was passed through it lengthwise, occupying the holes B and having its ends projecting and rounded to form gudgeons. The form was mounted with these gudgeons resting on horses, so that it could be rotated and thus wound with a narrow strip of thin steel plate. Thus sheathed, the form was lowered into the trench and the concrete was placed around it. When the arch had been turned, the wedges A were driven in until the ribs C dropped into the slots a and clear of the steel shell; the arch form was then pulled out and finally the invert form, leaving the steel shell in place to hold the concrete until hard. The strip of steel was then removed by pulling on one end until it unwound like cord from the inside of a ball of twine. Steel strips 6 ins. wide and 1/24 in. thick were used successfully in constructing a 5-ft. egg-shaped sewer in Washington, D. C. The forms were made in sections 16 ft. long, and were taken out as soon as the concrete had been placed. [Illustration: Fig. 248.--Sectional Steel Wrapped Wooden Form for Conduit Construction.] [Illustration: Fig. 249.--Invert Form for Conduit Construction.] The form shown by Fig. 249, is an invert form, used in constructing the sewer shown by Fig. 249, built at Medford, Mass., in 1902, by day labor. The concrete was 1-3-6 gravel. The forms for the invert were made collapsible and in 10-ft. lengths. The two halves were held together by iron clamps and hook rods. The morning following the placing of the concrete the hook rods were removed and turnbuckle hooks were put in their places, so that by tightening the turnbuckle the forms were carefully separated from the concrete. The concrete was then allowed to stand 24 hours, when the arch centers were set in place. These centers were made of 7/8×1½-in. lagging on 2-in. plank ribs 2 ft. apart, and stringers on each side. Wooden wedges on the forward end of each section supported the rear end of the adjoining section. The forward end of each section was supported by a screw jack placed under a rib 2 ft. from the front end. To remove the centers, the rear end of a small truck was pushed under the section about 18 ins.; an adjustable roller was fastened by a thumb screw to the forward rib of the center; the screw jack was lowered allowing the roller to drop on a run board on top of the truck; the truck was then pulled back by a tail rope until the adjustable roller ran off the end of the truck; whereupon the truck was pulled forward drawing the center off the supporting wedges of the rear section. Each lineal foot of sewer required 1¼ cu. yds. of excavation which cost 74.2 cts. per foot, and 1 cu. ft. of brick arch which cost $12.07 per cu. yd., or 44.2 cts. per lineal foot of sewer. The invert required 4 cu. ft. of concrete per foot, which cost as follows: Item. Per cu. yd. Portland cement at $2.15 per bbl. $2.292 Labor mixing and placing 3.017 Cost of forms 0.187 Labor screening gravel 0.471 Carting 0.592 Miscellaneous 0.146 ------ Total $6.705 The cost of the invert was thus $1.002 per lin. ft. of sewer. Collapsible metal forms for manholes and catch basins are made by several firms which make block and pipe molds. A cylindrical wooden form construction is shown by Fig. 250. The outside form consists of three segments of a cylinder made of 2-in. lagging bolted to hoops. Bent lugs on the ends of the hoops, were provided with open top slots and were bolted together through 1×3/8-in. bars which extended the full length of the form between lugs. The assembled form was collapsed by pulling up on the bars, thus lifting the bolts out of the slots. The inner mold is also made in three sections with strap hinges at two of the joints and at the third joint a wedge-shaped stave. The other details are shown by the drawing. To mold the top of the basin two cone-shaped forms are used, an outer form made in one piece and an inner form made in sections. Some 26 catch basins were built in Keney Park, Hartford, Conn., by Mr. H. G. Clark, at a cost of $7 apiece for concrete in place, and there was closely 1 cu. yd. of concrete in each. [Illustration: Fig. 250.--Form for Circular Catch Basin or Manhole.] ~CONCRETING.~--Except for pipes of small diameter, the concreting is done in sections, each section being a day's work. Continuity of construction has not proved successful, except for pipes of moderate size, in the few cases where it has been tried. Examples of continuous construction methods are given in succeeding sections. Methods of molding and laying cast concrete pipe are also best shown by the specific examples given further on. In concreting large diameters, the work may be done by molding successive full barrel sections, or by molding first the invert and then the roof arch, each in sections. The engineer's specifications generally stipulate which plan is to be followed. Construction joints between sections are molded by bulkhead forms framed to produce the type of joint designed by the engineer; the most common type is the tongue and groove joint. [Illustration: Fig. 251.--Cross-Section of Pinto Creek Irrigation Conduit.] For small diameters built with traveling forms, a comparatively dry concrete is essential, but when the centers are left in place until the concrete has set, a wet mixture is preferable, as it is more easily placed and worked around the reinforcement in the thin shells. Mixers are commonly specified even for small work, because of their generally more uniform and homogeneous product. Portable mixers hauled along the bank and discharging into the forms through chutes, furnish a cheap and rapid arrangement where the section being built has a considerable yardage. The examples given in succeeding sections present various methods of mixing and placing concrete in conduit work. [Illustration: Fig. 252.--Traveling Form for Pinto Creek Conduit.] ~REINFORCED CONDUIT, SALT RIVER IRRIGATION WORKS, ARIZONA.~--The pipe had the cross-section shown by Fig. 251, and formed a syphon carrying water under the bed of a creek. The concrete was a 1-2½-4 fine gravel mixture, mixed by hand on boards 150 ft. apart along the line. The shell was reinforced as shown. The forms consisted of an outside form constructed as shown by Fig. 251, by inserting 2½-in.×5½ ft. lagging strips in the metal ribs. The inside form was designed to permit continuous work by moving the form ahead as the concreting progressed. It consisted as shown by Fig. 252, of an invert form on which an arch form was carried on rollers. The invert form was pulled along by cable from a horsepower whim set ahead, being steered, aligned and kept to grade by being slid on a light wooden track. It had the form of a long half cylinder, with its forward end beveled off to form a scoop-like snout. The arch center consisted of semi-circular rings 2 ft. long, set one at a time as the work required. Each ring, when set, was flange-bolted to the one behind, and each was hinged at three points on the circumference to make it collapsible. In operation, the invert form was intended to be pulled ahead and the arch rings to be placed one after another in practically a continuous process. So that the arch rings might continue supported after the invert form was drawn out from under them, invert plates similar to the arch plates were inserted one after another in place of the shell of the invert form. The plan provided very nicely for continuous work, but continuous work was found impracticable for all but about 2,500 ft. of the 6,000 ft. of conduit built. The reason for this seems to have been at least in a great measure, the slow setting cement made at the cement works established by the Government, at Roosevelt. In building the first 300 ft. of conduit, a commercial cement was used and a progress of 120 lin. ft. of pipe per 24 hours was easily made. This work was done in June. Later, but still in warm weather, using the Government cement and 70 ft. of arch plates, not more than 70 ft. of pipe could be completed in 24 hours; if the plates were taken down sooner, patches of concrete fell out or peeled off with them. As the weather grew colder, this difficulty increased, until finally, the idea of continuous work was abandoned and for some 3,500 ft. of conduit only one 8-hour shift per day was worked. In December and January the plates had to remain in place three days, so that the progress was only 24 ft. per day; in warm weather this rate was increased to 40 ft. per day. Costs were kept on two sections of one of the lines and the figures shown in the accompanying table were obtained. A gang consisted of a foreman at $175 per month, a sub-foreman at $3.50 per day, and the following laborers at $2.50 per day: one bending the reinforcement rings; two placing the reinforcement; four taking down, moving and erecting the stationary plates; four placing the concrete and outside lagging; two wheeling concrete; six mixing concrete; one wheeling sand and gravel; one watering the finished pipe; four laying track for the steering apparatus, moving the superstructure and hangers, mixing boards, runways, etc.; one pointing and finishing inside the pipe; and one on the whim and doing miscellaneous work. The labor was principally Mexican, and only fairly efficient. It is important to note that the costs given in the table are labor costs only of mixing and placing concrete and moving forms; they do not include engineering, first cost of forms, concrete materials, reinforcement or grading. May, '06. July, '06. Wages 714 1,009 Cost Per Per Lin. Ft. Lin. Ft. Per Cu. Day. Cost. Cost. Lin. Ft. Yd. { Laying track for { steering alligator $ 5.00 $ 71.48 $ 43.98 $0.0670 $0.16 4 men { Moving and erecting { superstructure 5.00 299.94 358.44 0.3821 0.93 4 men Moving plates 10.00 202.50 253.44 0.2646 0.65 Repairs to alligator 58.50 2.50 0.0354 0.08 1 man Bending rings 2.50 32.87 59.87 0.0538 0.13 2 men Placing reinforcement 5.00 126.94 138.13 0.1538 0.38 12 men Mixing and placing concrete 30.00 709.68 949.74 0.9631 2.34 1 man Watering finished pipe. 2.50 45.00 78.27 0.0716 0.17 1 man Painting and brush-coating inside 2.50 96.50 117.37 0.1241 0.31 Blacksmith's work 30.00 25.00 0.0319 0.08 1 man Whim 2.50 23.87 28.75 0.0306 0.07 1 man Screening and hauling sand and gravel 2.50 183.13 300.00 0.2804 0.68 --------- --------- ------- ----- Total $1,880.41 $2,335.49 $2.4584 $5.98 ~CONDUITS, TORRESDALE FILTERS, PHILADELPHIA, PA.~--At the Torresdale plant of Philadelphia filtration system the clear water conduits are reinforced concrete. The following description is composed from information furnished the authors in 1904 by the Bureau of Filtration, Mr. John W. Hill, then chief engineer. The lengths of the several conduits are as follows: 576 ft. of 7½-ft., 782 ft. of 8-ft., 1,050 ft. of 9-ft., and 1,430 ft. of 10-ft. horseshoe conduit. All sizes of conduit have the same cross-sectional form--the cross-section of the 9-ft. conduit is shown by Fig. 253, and all are reinforced by expanded metal arranged as indicated. The concrete is a 1-3-5, ¾-in. stone mixture. The conduits were first designed with circular sections, but before construction had been begun on these plans, experience had been obtained in building a circular sewer that made a change to the horseshoe section appear desirable. In the circular sewer work, great difficulty had been found in properly placing and ramming the concrete in the lower quarters of the circular section. [Illustration: Fig. 253.--Section of 9-ft. Conduit, Philadelphia Filter Plant.] _Forms._--The forms used for the several sizes of conduit were all of the same general type, but improvements in detail were made as successive sizes were built. The last form to be designed was that for the 9-ft. section and this was the best one; it is shown by Fig. 254. The forms were built in sections from 12 ft. to 13½ ft. long. They were covered with No. 27 galvanized sheet iron, and this covering was found of advantage both in giving a smooth finish and in prolonging the life of the centers. The important feature is the construction in sections which could be set up and broken down by simply inserting and removing the connecting bolts. Three sets of forms were made for each size of conduit. [Illustration: Fig. 254.--Form for 9-ft. Conduit Philadelphia Filter Plant.] _Procedure of Work._--The first operation in building a section of conduit was to set to exact line and grade and the length of the form in advance of the finished work the bulkhead shown by Fig. 255. In this space the invert concrete was deposited and formed to a plane 1 in. below the finished invert bottom. The two bottom sections of the form were then assembled and located by bolting one end to the last preceding form and inserting the other end into the bulkhead. About two tons of pig iron were then placed on the invert form to keep it from floating while the liquid granolithic mixture was being poured into the 1-in. space between the form and the invert concrete. In building up the sides a facing form was used for placing the granolithic finish. This consisted of "boards" of sheet steel ribbed transversely on one side with ¾-in. pipe and on the other side with 1½-in. pipe. Two boards were used on each haunch, slightly lapping in the center, as follows: The board was placed with the small ribs against the form and the larger ribs kept the expanded metal just 3 ins. from the face of the form. A 6-in. depth of concrete was placed between the metal board and the outside form or planks, then 6 ins. of granolithic was poured into the 1-in. space between the center and the board and finally the board was raised 6 ins. and the concrete and granolithic mixture tamped together. With the board in its new position, another layer of concrete and granolithic was placed. Toward the crown the granolithic mixture was made stiff and simply plastered onto the mold. The expanded metal was cut into sheets corresponding to the length of the sides of the form and lapped 6 ins. in all directions; the bulkhead having a slot as shown to permit the metal to project 6 ins. from the face of the concrete in order to tie two sections together and also having a rib which formed a mortise in the face of the shell of concrete to key it to the succeeding section. [Illustration: Fig. 255.--Bulkhead Form for Conduits, Philadelphia Filter Plant.] All the conduits were built in sections from 12 ft. to 13½ ft. long, and there was very little, if any, difference in the labor required to build a section, in from eight to ten hours, of any of the three sizes. One foreman and 18 men on the top of the trench mixed and handled the concrete and granolithic mortar while one foreman, one carpenter and seven men in the trench set the forms and placed and rammed the concrete for one section in generally eight hours. About one-third of the concrete for the whole work was mixed in a portable cubical mixer of ½ cu. yd. capacity, and the remainder was mixed by hand. Owing to the relatively small amount of concrete used per day, about 20 cu. yds., it was found that there was practically no difference in the cost of machine mixing and of hand mixing. The 9-ft. conduit as an average of the three sizes, contained 20 cu. yds. of concrete, 1,200 sq. ft. of expanded and required 125 bags of cement for a section 13½ ft. long. The cost of the work excluding excavation and profit, but including forms, metal, concrete materials and labor, was about $10.50 per cu. yd. ~CONDUIT, JERSEY CITY WATER SUPPLY.~--In constructing the 8½-ft. reinforced concrete conduit for the Jersey City water supply, use was made of forms without bottoms. Each form was made of segmental sections 12½ ft. long of wood covered with sheet steel. They were set end to end in the trench, resting on 6-in. concrete cubes which were finally permanently embedded in the invert concrete. In each form there was a scuttle about 2 ft. square at the crown, and the bottom was open between the curves of the invert haunches. The form being set and greased and the reinforcement placed, the concrete was deposited on the outside and forced by means of tamping bars down the curve of the invert haunches until it filled the whole space between the form and the earth and appeared at the edges of the bottom opening in the form. Concrete was then thrown through the scuttle and the invert screeded into shape. The concreting of the sides and crown of the arch was then completed, using outside forms except for about 5 ft. of the crown, the scuttle, of course, being closed by a fitted cover. The centers were left in place about 48 hours. The concrete was a 1 cement 7 sand and run of the crusher 2-in. broken stone mixture, and was made so wet that it would flow down an incline of 1 on 8. The mixing was done in portable Ransome mixers, set on the trench bank alongside the work and discharging by chute into dished shoveling boxes provided with legs to set on the erected forms. Coal scoops were used in shoveling from the box into the forms and were found superior to shovels in keeping the relative proportions of water and solids constant. ~TWIN TUBE WATER CONDUIT AT NEWARK, N. J.~--In constructing the Cedar Grove Reservoir, at Newark, N. J., two conduits side by side were built across the bottom from gate house to tunnel outlet. A section of one of the conduits showing the form construction and the arrangement of the reinforcement is given by Fig. 256. The concrete was a 1-2-5 1½-in. stone mixture and the reinforcement was No. 10 3-in. mesh expanded metal. The method and cost of construction are given as follows, by Mr. G. C. Woollard, the engineer for the contractors. [Illustration: Fig. 256.--Conduit for Cedar Grove Reservoir, Newark. N. J.] "The particular thing that was insisted upon by both Mr. M. R. Sherrerd, the chief engineer of the Newark Water Department and Mr. Carlton E. Davis, the resident engineer at Cedar Grove Reservoir, in connection with these conduits, was that they be built without sections in their circumference, that the whole of the circumference of any one section of the length should be constructed at one time. They were perfectly willing to allow us to build the conduit in any length section we desired, so long as we left an expansion joint occasionally which did not leak. "The good construction of these conduits was demonstrated later, when the section stood 40 lbs. pressure to the square inch, and, in addition, I may say that these conduits have not leaked at all since their construction. This shows the wisdom of building the conduit all round in one piece, that is, in placing the concrete over the centers all at one time, instead of building a portion of it, and then completing that portion later, after the lower portion had had an opportunity to set. "The centers which I designed on this work were very simple and inexpensive, as will be gathered from the cost of the work, when I state that this conduit, which measured only 0.8 cu. yd. of concrete to the lineal foot of single conduit, cost only $6.14 per cu. yd., built with Atlas cement, including all labor and forms and material, and expanded metal. The forms were built in 16 ft. lengths, each 16 ft. length having five of the segmental ribbed centers such as are shown in Fig. 256, viz., one center at each end and three intermediate centers in the length of 16 ft. These segments were made by a mill in Newark and cost 90 cts. apiece, not including the bolts. We placed the lagging on these forms at the reservoir, and it was made of ordinary 2×4 material, surfaced on both sides, with the edges beveled to the radius of the circle. These pieces of 2×4 were nailed with two 10d. nails to each segment. The segments were held together by four ½-in. bolts, which passed through the center, and 1½-in. wooden tie block. There was no bottom segment to the circle. This was left open, and the whole form held apart by a piece, B, of 3×2 spruce, with a bolt at each end bolted to the lower segment on each side. "The outside forms consisted of four steel angles to each 16 ft. of the conduit, one on each end, and two, back to back, in the middle of each 16 ft. length. These angles were 2×3, with the 2-in. side on the conduit, and the 3-in. side of the angle had small lugs bolted on it at intervals, to receive the 2×12 plank, which was slipped down on the outside of the conduit, as it was raised in height. The angles were held from kicking out at the bottom by stakes driven into the ground, and held together at the top by a 2½-in. tie-rod. "The conduit was 8 ins. thick, save at the bottom, where it was 12 ins. The reason for the 12 ins. at the bottom was that the forms had to have a firm foundation to rest on, in order to put all the weight required by the conduit on them in one day or at one time, without settling. We therefore excavated the conduit to grade the entire length, and deposited a 4-in. layer of concrete to level and grade over the entire length of the conduit line. This gave us a good, firm foundation, true and accurate to work from, and this is the secret of the good work which was done on these conduits. If you examine them, you will say that they are one of the neatest jobs of concrete in this line that has been built, especially with regard to the inside, which is true, level and absolutely smooth. [The authors can confirm this statement.] When the conduit is filled with water, it falls off with absolutely no point where water stands in the conduit, owing to its being out or the proper amount of concrete not being deposited. "The centers were placed in their entirety on a new length of conduit to be built, resting upon four piles of brick, two at each end as shown. The first concrete was placed in the forms at the point marked X and the next concrete was dropped in through a trap door cut in the roof of the conduit form at the point marked Y. This material was dropped in to form the invert, and this portion was shaped by hand with trowels and screeded to the exact radius of the conduit. The concrete was then placed continuously up the sides, and boards were dropped in the angles which I have mentioned, and which served as outside form holders till the limit was reached at the top, where it was impossible to get the concrete in under the planking and thoroughly tamped. At this point the top was formed by hand and with screeds. "Each 16-ft. length of this conduit was made with opposite ends male and female respectively, that is, we had a small form which allowed the concrete to step down at one end to 3 ins. in thickness for 8 ins. back from the end of the section, and on the other end of the section it allowed it to step down to 3 ins. in thickness in exactly the opposite way, making a scarf joint. This was not done at every 16 ft. length, unless only 16 ft. were placed in one day. We usually placed 48 ft. a day at one end of the conduit with one gang of men. This was allowed to set 24 hours, and, whatever length of conduit was undertaken in a day, was absolutely completed, rain or shine, and the gang next day resumed operations at the other end of the conduit on another 48 ft. length. This was completed, no matter what the weather conditions were, and, towards the close of this day the forms placed on the preceding day were being drawn and moved ahead. "The method used in moving these forms ahead for another day's work is probably one of the secrets of the low cost of this work, and it is one which we have never seen employed before. The bolt at A, Fig. 256, was taken out, and the tie brace B thrown up. We had hooks at the points C. A turnbuckle was thrown in, catching these hooks, and given several sharp turns, causing the entire form to spring downward and inwards, which gave it just enough clearance to be carried forward, without doing any more striking of forms than pulling the bolt at A. This method of pulling the forms worked absolutely satisfactorily, and never gave any trouble, and we were able to move the forms very late in the day and get them all set for next day's work, giving all the concrete practically 24 hours' set, as we always started concreting in the morning at the furthest end of the form set up and at the greatest distance from the old concrete possible in the 48 ft. length, as the furthest form had, of course, to be moved first, it being impossible to pass one form through the other. "Six 16-ft. sections of these forms were built, and three were used each day on each end, as shown by the diagram MN, Fig. 256, which gives the day for the month for the completion of each of seven 48-ft. sections. "A gang of men simply shifted on alternate days from end to end of the conduit, although several sections were in progress at one time; and of course, finally, when a junction was made between any division, say of 1,000 ft. to another 1,000 ft., one small form was left in at this junction inside of the conduit, and had to be taken down and taken out the entire length of the conduit. "The centers for a 16-ft. length of this conduit cost complete for labor and material, $18.30, but they were used over and over again; and, after this conduit was completed, they were taken away for use at other points, so that the cost is hardly appreciable, and the only charge to centers that we made after the first cost of building the centers, was on account of moving them daily. Part of this conduit was built double (two 6-ft. conduits) and part single, the only difference being that, where the double conduit was built, two forms were placed side by side, and not so much was undertaken in one day. "These conduits, when completed and dried out, rung exactly like a 60-in. cast-iron pipe, when any one walked through them or stamped on the bottom." Mr. Woollard gives the following analysis of the cost per cubic yard of the concrete-steel conduit above described: Per cu. yd. 1.3 bbl. cement $1.43 10 cu. ft. sand 0.35 25 cu. ft. stone 1.10 26 sq. ft. expanded metal, at 3 cts. 0.78 Loading and hauling materials 2,000 ft. to the mixing board (team at $4.50) 0.50 Labor mixing, placing, and ramming 1.38 Labor moving forms 0.60 ----- Total $6.14 Wages were 17½ cts. per hr. for laborers and 50 cts. per hr. for foremen. The concrete was 1-2-5, a barrel being assumed to be 3.8 cu. ft. The concrete was mixed by hand on platforms alongside the conduit. The cost of placing and ramming was high, on account of the expanded metal, the small space in which to tamp, and to the screeding cost. When forms were moved they were scraped and brushed with soft soap before being used again. From Mr. Morris R. Sherrerd, Engineer and Superintendent, Department of Water, Newark, N. J., we have received the following data which differ slightly from those given by Mr. Woollard. The differences may be explained by the fact that the cost records were made at different times. Mr. Sherrerd states (Sept. 26, 1904,) that each batch contains 4 cu. ft. of cement, 8 cu. ft. of sand, and 20 cu. ft. of stone, making 22 cu. ft. of concrete in place. One bag of cement is assumed to hold 1 cu. ft. He adds that a 10-hour day's work for a gang is 63 lin. ft. of single 6-ft. conduit containing 47.4 cu. yds. of concrete and 1,260 sq. ft. of expanded metal. This is equivalent to ¾ cu. yd. of concrete per lin. ft. The total cost of material for one complete set of forms 64 ft. long was $160; and there were 7 of these sets required to keep two gangs of men busy, each gang building 63 lin. ft. of conduit a day. Since the total length of the conduit was 3,850 ft., the first cost of the material in the forms was 18 cts. per lin. ft. Cost of Labor on 6-ft. Conduit: Per day. Per cu. yd. 1 foreman on concrete $ 3.35 $0.07 1 water boy 0.75 0.01 11 men mixing at $1.75 19.25 0.39 5 men mixing at $1.50 7.50 0.16 4 men loading stone at $1.40 5.60 0.12 4 men wheeling stone at $1.40 5.60 0.12 2 men loading sand at $1.40 2.80 0.06 2 men wheeling sand at $1.40 2.80 0.06 1 man placing concrete at $1.75 1.75 0.04 6 men placing concrete at $1.50 9.00 0.19 2 men supplying water at $1.50 3.00 0.06 1 man placing expanded metal at $2. 2.00 0.04 1 man placing expanded metal at $1.50 1.50 0.03 ------ ----- Total labor on concrete $64.90 $1.35 Cost of Labor Moving Forms: Per day. Per cu. yd. 4 carpenters placing forms $13.00 $0.27 2 helpers placing forms 4.00 0.08 1 carpenter putting up boards for outside forms 2.75 0.06 1 helper putting up boards for outside forms 2.25 0.05 2 helpers putting up boards for outside forms 3.50 0.07 1 team hauling timber 4.50 0.09 1 helper hauling lumber 1.75 0.04 ------ ----- Total labor moving $31.75 $0.66 It will be noted that it required two men to bend and place the 700 lbs., or 1,260 sq. ft., of expanded metal required for 63 lin. ft. of conduit per day, which is equivalent to ½c per lb., or 3 cts. per sq. ft., for the labor of shaping, placing and fastening the metal. ~CIRCULAR SEWER, SOUTH BEND, INDIANA.~--In building 2,464 ft. of 66-in. circular reinforced concrete sewer at South Bend, Ind., in 1906, the method of construction illustrated in Figs. 257, 258 and 259 was employed. The sewer has a 9-in. shell buttressed on the sides and is reinforced every 12 ins. by a 3/16×1-in. peripheral bar in the sides and roof and 3 ins. in from the soffit. Each bar is composed of three pieces, two side pieces from 15 ins. below to 6 ins. above springing lines and a connecting roof bar attached to the side bars by cotter pins. Two grades of concrete were used, a 1-3-6 bank gravel concrete for the invert and a 1-2-4 bank gravel concrete for the arch. The invert was given a ½-in. plaster coat of 1-1 mortar as high as the springing lines. [Illustration: Fig. 257.--Form for South Bend Sewer (First Stage).] [Illustration: Fig. 258.--Form for South Bend Sewer (Second Stage).] [Illustration: Fig. 259.--Form for South Bend Sewer (Third Stage).] Forms and Concreting.--In constructing the sewer the trench was excavated so as to give a clearance of 1 ft. on each side and was sheeted as shown by Fig. 257. The sewer was built in 12 ft. sections as follows: The bottom of the trench was shaped as nearly as possible to the grade and shape of the base of the sewer. Four braces to each 12 ft. section were then nailed across the trench between the lowest rangers on the trench sheeting. A partial form consisting of a vertical row of lagging was set on each of the outside lines of the sewer barrel as shown by Fig. 257. Each section of this lagging was held by stakes driven into the trench bottom and nailed at their tops to the cross braces as shown by Fig. 258. A template for the invert was then suspended from the cross braces by pieces nailed to the four ribs of the template and to the cross braces as shown by Fig. 257. The concrete was now placed and carried to the top of the template, which was then removed. The side pieces of the reinforcing bars were then set and fastened as shown by Fig. 258. The side forms extending up to the springing lines were then placed. They were held in position by braces nailed to their ribs at the tops and by other braces fitting into notches in the ends of their ribs at the bottom. The concrete was then carried up to the springing lines, the arch centers in two pieces were placed; the arch bar of the reinforcement was placed and the extrados forms erected up to the 45° lines, all as shown by Fig. 259. The placing of the arch concrete completed the sewer barrel. The outside forms and bracing were removed about 24 hours after the completion of the arch and back filling the trench was begun immediately, but the inside forms were left in place for two weeks; they were then removed by the simple process of knocking out the notched braces. By building several lengths of invert first and following in succession by the side wall construction and then by the arch construction, the form erection and the concreting proceeded without interruption by each other. It was also found that, by making bends in the form of polygons with 10 ft. sides instead of in the form of curves, there was a material saving in expensive form work. To overcome the friction of the angles in such bends an additional fall was provided at these places. All concrete was made in a Smith mixer mounted on trucks so that it could be moved along the bank of the trench and discharging into a trough leading to the work. _Labor Force and Cost._--With a gang of 12 men from 24 to 36 ft. of sewer was built per 10-hour day, working only part of the time on actual concreting. The disposition of the force mixing and laying concrete and the wages were as follows: Item. Per day. Six wheelers, at 18.5 cts. per hour $11.10 One mixer, at 22.5 cts. per hour 2.25 One dumper, at 18.5 cts. per hour 1.85 Four placers, at 22.5 cts. per hour 9.00 ------ Total $24.20 There were 0.594 cu. yd. of concrete per lineal foot of sewer and its cost is given as follows: Item. Per cu. yd. Cost of gravel $0.774 Cost of sand 0.36 Cost of cement 1.50 Cost of steel reinforcement 0.84 Cost of labor, mixing and placing concrete 1.094 Cost of moving forms, templates, etc. 0.757 Cost of forms, templates, etc. 0.589 Cost of finishing, plastering, etc. 0.639 Cost of tools and general expenses 0.841 ------ Total $7.394 ~SEWER INVERT, HAVERHILL, MASS.~--In constructing sewers with concrete inverts at Haverhill, Mass., in 1905, use was made of the traveling form or mold shown by Fig. 260. The form consists of an inner and an outer shell, the annular space between which forms the mold; in operation the annular space is filled with concrete, then the outer shell is pulled ahead from underneath, leaving the inner shell in place. A second inner shell is then adjusted to the outer shell in its new position, the annular mold is concreted and the outer shell again pulled ahead. Continued repetition of the operations described completes the invert. The merit of the device lies in the fact that the inner shell is not moved until the concrete has attained some degree of rigidity; when, in such devices, the inner mold is slid ahead on the green concrete it is likely so to "drag" forward the material that a rough and pitted surface results. _Mold Construction._--Referring to the drawings of Fig. 260, A is the outer mold of sheet steel bent to the required shape of the outer surface of the conduit to be constructed. A rib, or angle, B, is riveted to the inside of the mold at its front end and a diaphragm C of plank is securely fastened to the rear side of the rib. The opposite or rear end of the mold is open. Angles D forming tracks are riveted inside the mold a short distance below the edges and reaching their full length. The inner mold comprises a steel shell E curved to the form of the inside of the conduit; inside this steel shell is a reinforcing lagging, and at each end there is a wooden diaphragm F. Passing through both end diaphragms and having its ends flush with the end planes of the mold is a timber G. Rearward projecting lips e are secured to the lagging at the rear end of the mold and on each side of the timber G. The diaphragms F have each two arms f which project horizontally beyond the surface of the inner mold and engage the tracks D; locking dogs H are pivoted to the arms f so as to hook under the track angles D and hold the inner form from rising. Setting on the inner mold is an inverted V-shaped deflector I; its edges are flush with the sides of the mold and its purpose is to facilitate the placing of the concrete. There is also a movable diaphragm K, fitting loosely inside the outer mold A and bearing against the end of the inner mold E. The length of the inner mold E is about one-half that of the outer mold A; as a rule several inner molds are provided with one outer mold. [Illustration: Fig. 260.--Traveling Invert Form for Sewer Construction.] _Mode of Operation._--In using the device described the outer mold A is first placed in the trench with its rear end at the end of the trench. An inner mold E is then suspended on the tracks of the outer mold and locked therein by the dogs H, with its rear end flush with the rear end of the outer mold. The partition K is then placed in position against the forward end of the inner mold and a jack J of any suitable form is interposed between diaphragms K and C, the jack being extended sufficiently to press diaphragm K firmly against the front end of the inner mold. The deflector I is next placed in position on the inner mold and the concrete is forced down with an iron rammer between the two molds, so as to fill completely the annular space. The deflector aids in directing the concrete into this space, as will be obvious. After the mold has been filled and the concrete compacted as much as possible, the jack is operated to separate the diaphragms K and C, and as the partition K is pressed against one end of the mass of concrete which has been laid, the opposite end of which abuts against the end of the trench, it follows that any backward movement of the diaphragm K will compress the concrete. This movement will be practically inappreciable in distance, but enough to compact thoroughly the concrete and fill any voids. The action of the jack will also push forward the diaphragm C and the outer mold A, the latter being withdrawn from beneath the inner mold and the newly laid concrete, the tracks D of the outer mold being drawn from beneath the arms f of the inner mold, leaving the latter behind resting on the freshly laid concrete. Further compression of the concrete after it has been left by the outer mold will fill the spaces between the inner mold and the surface of the trench. The outer mold is moved forward in this manner a distance equal to the length of the inner mold, and then the diaphragm K is drawn forward and another inner mold is lowered into the outer mold exactly as was the first one. The jack is then placed, the concrete deposited and the outer mold again advanced exactly as before. As the outer mold advances, the inner molds become disengaged one after another and are set ahead; in practice, enough inner molds are provided to enable the concrete to harden sufficiently to keep its position when it becomes necessary to take up successively the rearmost molds and place them ahead. _Haverhill Sewer Work._--The work at Haverhill, Mass., previously mentioned in which the form just described was used, was a 24-in. circular sewer with 6-in. walls. The outer form was 36 ins. in diameter and 6 ft. 2 ins. long; the inner form was 24 ins. in diameter and 3 ft. long. Angle B was 3 ins. and the track angles D were 1½ ins.; diaphragm K was made of two thicknesses of 3-in. plank and diaphragm C of one thickness of 3-in. plank, the other diaphragms were of 2-in. plank. The shells of the molds were of ¼-in. steel plate; the jack was an ordinary screw jack. Eight inner molds were used. The form used at Haverhill was built by the city carpenter, the metal portions being made in a boiler shop. Its cost was not ascertained, but was, it is thought, about $75. The concrete used was a 1-3-5 stone mixture, with cement costing $2 per barrel, sand $1.50 per load of 36 cu. ft., and stone $2.50 per load of 36 cu. ft. The men were paid 25 cts. per hour. Records kept on 265 ft. of invert, or, theoretically, 19.3 cu. yds. of concrete, gave the following figures: Per Per lin. ft. cu. yd. Labor, setting and moving forms, 42 hours, at 25 cts. $0.05 $0.67 Labor, mixing, placing and wheeling concrete, 179 hours, at 25 cts. 0.16 2.19 ----- ----- Total labor cost $0.21 $2.86 With the ordinary 1-3-5 mixture the cost of materials would run about as follows: Per cu. yd. Cement, 0.96 bbl., at $2. $1.92 Sand, 0.47 cu. yd., at $1.13 0.53 Stone, 0.78 cu. yd., at $1.88 1.47 ----- Total cost materials $3.92 Two men were worked in the trench, one alternately ramming the concrete into place and working the jack, and the other shaping the trench ahead and assisting in bringing the rear forms ahead. The form described was invented by Mr. Robert R. Evans, of Haverhill, Mass., and has been patented by him. ~29-FT. SEWER, ST. LOUIS, MO.~--The following account of the method and cost of constructing 162 ft. of very large sewer section at St. Louis, Mo., is compiled from information furnished by Mr. Curtis Hill. The cross-section of the sewer is given by Fig. 261, which also shows the arrangement of the reinforcing bars. Johnson corrugated bars, old style, are used for reinforcement. The sections of the various reinforcing bars are: Longitudinal bars, 0.18 sq. in.; invert bars, 0.7 sq. in., and arch bars, 0.7 sq. in. The spacing of the bars and the arrangement of the splices are indicated on the drawings of Fig. 261. All splices have a lap of 36 ins. Some gravel concrete has been used in the invert, but most of the concrete has been crushed limestone and Mississippi River channel sand. The proportions were 1-3-6 in the invert and 1-2-5 in the arch. The arch was computed by Prof. Greene's method. The ultimate strength of concrete in compression was taken as 2,000 lbs. per sq. in. and the working strength at 500 lbs. per sq. in. The elastic limit of the reinforcing bars was taken at 50,000 lbs. [Illustration: Fig. 261.--Harlem Creek Sewer, St. Louis, Mo.] The trenching was done by wheel scrapers to the amount of waste. Then a cableway was erected spanning the entire length of the section and the remainder of the material taken out. The last 4 or 5 ft. in depth were in limestone and the excavated rock was taken by cableway to dump carts which took it to the crusher and returned with crushed rock to be used for concrete. This rock foundation was taken advantage of to reduce the amount of invert concrete. In constructing the sewer proper the invert was first concreted to template to the height shown in Fig. 262. The arch forms were then placed as shown in Fig. 262, and the roof arch concreted. Both templates and arch forms were constructed of wood. The arch forms were moved ahead on iron rails and jacked into place. The ribs were 2×10-in. pieces and were spaced 4 ft. on centers; the lagging was 2-in. tongue and grooved stuff and was smeared with crude oil. The reinforcing bars shown in Fig. 261 were bent to proper radius by means of a wagon tire bender and were held in place by templates. The concrete was all mixed by two Chicago Improved Cube mixers operated by electric power. [Illustration: Fig. 262.--Center for Harlem Creek Sewer.] The cost records of constructing the section of 29-ft. sewer so far built are not susceptible of complete analysis, but the following figures can be given. The prices of materials were as follows: Cement, per barrel $1.80 Sand, per cubic yard 0.75 Broken stone, per cubic yard 1.00 Reinforcing bars, per pound 0.02 Vitrified brick, per 1,000 12.00 The wages paid different classes of labor were: Per hour. Firemen $0.50 Laborers 0.175 Laborers 0.20 Laborers 0.25 Laborers 0.28 Laborers 0.3025 Bricklayers 0.66 2/3 Helpers $0.25 Carpenters 0.55 Engineers 0.50 Timekeepers 0.25 Watchmen 0.175 Hostlers 0.175 Teams 0.60 Taking up the several items of work in order, the excavation amounted to 21,400 cu. yds., of which 1,400 cu. yds. were rock excavation. The cost of excavation was as follows: Total. Per cu. yd. Earth, excavation $7,640 $0.38 Earth bracing 2,000 0.10 Rock excavation 1,400 1.00 Rock, dynamite, tools, etc. 560 0.40 The cost of crushing the excavated rock and returning it to the mixer was $1 per cu. yd. The cost of the concrete work was as follows: Per cu. yd. 1.30 bbl. cement at $1.80 $2.34 .044 cu. yd. sand at 75 cts. 0.33 1 cu. yd. broken stone at $1 1.00 ----- Total concrete materials $3.67 There were 1,600 cu. yds. of concrete placed at a cost of for: Total. Per cu. yd. Mixing and placing $1,180 $0.7375 Forms 2,000 1.25 Moving forms 400 0.25 ------ ------- Total for forms and labor $3,580 $2.2375 For reinforcing the concrete 86,600 lbs. of steel, or about 55 lbs. per cu. yd. were used. The cost of placing and bending this steel was as follows: Total. Per lb. Cost of placing $172 0.1986 ct. Cost of bending 52 0.06 ct. We can now summarize the cost of the concrete work proper of this sewer as follows: Items. Per cu. yd. Cement, sand and stone $3.67 55 lbs. steel at 2 cts. 1.10 Forms, labor and materials 1.25 Mixing and placing concrete labor 0.74 Placing steel at 0.1986 ct. per lb. 0.11 Bending steel at 0.06 ct. per lb. 0.03 Moving forms 0.25 ----- Total labor and materials $7.15 To get the total cost of the sewer proper we must add the cost of the vitrified brick invert paving. There were 71 cu. yds. of this paving and its cost was as follows: Per cu. yd. 0.6 bbls. cement at $1.80 $1.08 0.25 cu. yd. sand at 75 cts. 0.19 450 bricks at $12 per M. 5.40 Labor laying, 71 cu. yds. at $180.33 2.54 ----- Total $9.21 None of the preceding figures includes the plant charges. The plant cost $12,000 and the cost of running it during the work described was $2,000. In explanation it should be noted that the plant served for building some 1,340 lin. ft. of 27-ft. sewer as well as for the section described. ~SEWER AT MIDDLESBOROUGH, KY.~--In constructing an oval sewer 4 ft. high at Middlesborough, Ky., two steel forms in 10-ft. sections were used. As shown in Fig. 263, T-iron ribs were spaced 5 ft. apart, fastened together at the top by longitudinal angle irons, and at the bottom by a sheet of steel 22 ins. wide, forming the bottom of the invert. The lagging for the sides consists of movable 5-ft. lengths of channel iron, secured by sliding bolts. After the bottom of the trench has been roughly shaped with concrete, a 10-ft. section of invert forms is lowered and suspended by the cross-beams, and the space beneath packed with concrete; then a channel iron is slid into place and bolted, and concrete packed behind it, and so on until the invert is made. The next 10-ft. section is then built while the first is hardening. Upon the completion of the second section, the channel iron sides of the first section are removed, and then the rib framework is lifted out. Wood arch centers are then put in place and an inch of 1:2 plaster spread over the lagging before placing the concrete for the arch, which is 6 ins. thick. [Illustration: Fig. 263.--Invert Form for Sewer Construction.] The cost per 100 ft. of this sewer was as follows (prices being assumed for cement and labor): Bottom concrete. Cost per 100 ft. 18.5 bbls. cement, at $1.50 $ 27.75 2.7 cu. yds. sand, at $1.00. 2.70 15 cu. yds. stone, at $1.00 15.00 17 days labor, at $1.50 25.50 Bottom concrete. Cost per 100 ft. 25.25 bbls. cement, at $1.50 37.85 7.5 cu. yds. sand, at $1.00 7.50 22 days labor, at $1.50 33.00 Sewer Arch. 26 bbls. cement, at $1.50 39.00 3.9 cu. yds. sand, at $1.00 3.90 13.6 cu. yds. stone, at $1.00 13.60 21 days labor, at $1.50 31.50 ------- Cost per 100 ft. $237.30 [Illustration: Fig. 264.--Sewer at Cleveland, Ohio.] ~INTERCEPTING SEWERS, CLEVELAND, O.~--An intercepting sewer some 3½ miles long, of the form and construction shown in Fig. 264, was built at Cleveland, Ohio, in 1904. The construction consists of a plain concrete invert lined with two courses of shale bricks, and having two rows of anchor bars set in the side walls so that the bars of one row are staggered with respect to those of the other row. The anchor bars are 2×½-in. steel, and are spaced 30 ins. apart in each row. To the anchor bars are bolted arch reinforcing bars arranged as shown, and these arch bars have bolted to them eight lines of 1½×¼-in. longitudinal bars. A natural cement concrete is used for the invert and side walls. The arch is Portland cement concrete of normally a 1-3-7½, 1½-in. screened stone mixture, but where the voids in the broken stone exceeded 40 per cent., it is a 1-3-6 mixture. The invert bricks are laid in Portland cement mortar and the arch has a mortar lining and is waterproofed with 1-in. of mortar on top. _Forms._--Separate forms were used for the invert and for the arch ring. Regarding these, the engineer, Mr. Walter C. Parmley, remarks: One of the first forms used in the sewer was like a piece of segmental arch centering inverted, and with the lagging nailed fast to the ribs. The trouble with this form is that it is difficult to tamp concrete under the bottom portion of the form, and hence a very rough surface is produced. Much better results were obtained by omitting the lagging boards on the bottom and at the sides till a point was reached where the inclination of the concrete surface was about 45°. The concrete for the bottom could then be worked down between the ribs, thorough tamping done, and a good surface obtained. The ribs serve as a guide, so that the workman produces the proper shape. From this point up to the vertical, good results can be secured with the ribs attached to the lagging. Some contractors found it more convenient to use ribs that were connected with each other by a skeleton framework only, and then to slip the lagging in, one piece at a time. For some of the sewers, in which the brick lining was not carried quite up to the spring line, a separate side form of skeleton ribs and loose lagging was set upon brace legs bearing on the bottom of the invert. This form carried the concrete from about 2 ft. below to about 2 ft. above the springing line. The arch ribs then became segmental and rested upon the middle braces. This method has the advantage of using ribs that are lighter and more easily handled than those that are semi-circular. For arch centering, it is necessary and convenient to use independent ribs and loose lagging, for the centers can then be carried forward piece-meal, the falsework upholding the green arch and re-erected at the advance end of the work. In these matters each contractor prefers to use his own ingenuity, and so long as the work is properly built, the engineer can well give him considerable latitude as to use of methods. One thing, however, the engineer must insist upon--that all centering and falsework be as nearly rigid as possible. Even a slight settlement of the centers at the crown under the load of concrete and back-fill will cause the arch to kick out at the quarters, and if the green concrete arch is not cracked at the crown, it will be crushed on the inside, about half way between the crown and springing line. A reinforced arch is no more immune to this danger than is a plain concrete arch. However, with a few days of hardening, although the damage may be serious, the danger of actual collapse is less. A point to be guarded against, especially in reinforced construction, is any foolish act on the part of contractor or workman, due to his overconfidence in the strength of the structure because it contains embedded steel. The mode of procedure in constructing the arch ring was to erect the centers with lagging complete. The lagging was then covered with building paper waterproofed with paraffine. The arch reinforcing bars were then bolted to the anchor bars and the longitudinals connected up. The lining of Portland cement mortar was first laid on the lagging. Before this mortar had set, concrete was rammed in between it and the sheeting to a height of 18 ins. above the springing line, and then the remainder of the concrete placed without outside forms. The top of the arch ring was finally finished with a 1-in. mortar coat. In regard to the concrete, Mr. Parmley remarks: "Concrete will flush up to the forms and produce a better surface, and the voids in the stone will be much better filled if it is so wet as to require but little tamping; moreover there is less danger of obtaining a weak, porous wall should a workman neglect thorough tamping, than there is where only a moist mixture is used. It is also to the contractor's interest to use wet concrete for much less labor is required in mixing and placing it. Small broken stone or gravel is preferable in concrete for sewers. The walls being comparatively thin, unless there be a considerable excess of mortar, if coarse stones are used, the concrete will be honeycombed with voids. The stones should be well graded in size from large to fine, but the largest fragments should not exceed 1½ ins. in greatest dimension." _Cost._--A number of records of cost of constructing short sections of the sewer described are given by Mr. Parmley, as follows: Labor placing anchor bars. Per day. 1 man, at $3.50 $3.50 1 man, at $1.75 1.75 4 hours carrying steel at 20 cts. 0.80 ----- $6.05 The anchor bars were placed for 40 lin. ft. of sewer, or about 1,504 lbs. of metal at a cost of 0.4 ct. per lb. The concreting gang for the sides consisted of: 5 men wheeling and mixing at $1.75 $8.75 1 man tamping 1.75 2/3 time man lowering brick and concrete at $2.25 1.50 1 man carrying concrete 1.75 ------ $13.75 This gang built the side wall for 40 ft. of sewer daily, or 13 cu. yds. Cost of labor per cu. yd. was, therefore, $1.06. The concrete was tamped behind the brick lining as the latter was built up by the mason. Cost of single ring brick lining at sides: 2 masons at 70 cents per hour $1.20 1 man mixing mortar 2.25 1/3 time man lowering at $2.25 0.75 3 men wheeling sand, filling buckets and dumping 5.25 ------ Total labor for 40 lin. ft. of sewer $19.45 Quantity of brick masonry laid, cu. yd. 6.38 Labor per cu. yd. 3.05 An account was kept of labor performed on 85 lin. ft. of arch work, or 14 1-6 ft. daily. The force was as follows: 1 man putting mortar lining on centering $1.75 2 men mixing mortar, screening and wheeling sand 3.50 1 man tamping concrete 1.75 8 men on mixing board at $1.75 14.00 ------ $21.00 No. cu. yd. placed daily 25.64 Labor per cu. yd. 0.82 Placing centering and arch bars: 2 men at $1.75 $3.50 1 man at $3.50 3.50 ----- $7.00 Costs, for 14 1-6 ft. daily, $0.49 per lin. ft. As nearly as could be judged, about two-thirds of the labor was used in erecting the centering and one-third in putting the steel in place. The amount of steel placed daily was 785 lbs., at cost, therefore, of 0.3 of a cent per lb., and the cost of erecting and moving centers, $0.33 per lin. ft. of arch. Another record of 39.27 ft. on a curve, gave for the cost of the brick work at sides the same result as above, but the inspector's record of men working on concrete backing at sides showed a less cost, as follows: 4 men mixing at $1.75 $7.00 2/3 time man lowering at $2.25 1.50 1 man in bottom 1.75 ----- $10.25 They placed 12.7 cu. yd. at a cost of $0.81 per cu. yd. This figure probably more nearly represents the average cost than the $1.06 reported in the first instance. The cost of placing the anchor bars on straight sewer, representing average progress, at another time, was found to be: 1 man $3.50 1 man 1.75 ----- $5.25 They placed the steel for 44 ft. of sewer or 1,650 lb. at a cost of 0.32 of a cent per lb. Further notes for 6 days' work, when it seemed to represent as nearly as possible the general average for the whole were: Labor on arch concrete: Daily progress was 13 1-6 ft. The force employed was: 7 men making concrete, at $1.75 $12.25 1 man plastering the center 1.75 1 man mixing mortar 2.00 1 man tamping 1.75 ----- $17.75 On straight arch work they placed 24.1 cu. yd. daily at a cost of $0.74 per cu. yd. In three days' work on a curve, the same gang placed 26.37 cu. yd. daily at a cost of $0.675 per cu. yd. On centering and steel for arch, three men kept up with the regular progress of the arch-concreting gang. The cost, therefore, is: 1 man $3.50 2 men at $1.75 3.50 ----- $7.00 They averaged 13 ft. daily, or at a total cost of about $0.54 per lin. ft. of sewer. Two-thirds of this labor was on the centering or $0.36 per lin. ft. of arch; $0.18 per lin. ft. placed the steel ready for embedding, or about 55.5 lb. per ft. of arch, at a cost of 0.32 of a cent per lb. For the double ring brick lining at the bottom, the regular daily rate of progress was 28 ft. or 11.15 cu. yd. with: 2 bricklayers $11.20 5 men at $1.75 8.75 1 man at $2.25 2.25 ----- $22.20 or at a cost of $1.98 per cu. yd. This is given only because it is of interest in connection with the cost of the concrete. Other observations on cost of placing steel skeleton and concrete did not vary materially from the figures given. It will be observed that no charge for superintendence or anything for the general expenses is included in the estimates of cost. These charges were, of course, impossible to obtain. On another contract with machine mixing, as high as 36 lin. ft. of 13 ft. 6 in. arch were built in a day, but no data as to cost were taken, though it was evidently less than for the work with hand-mixed concrete. ~REINFORCED CONCRETE SEWER AT WILMINGTON, DEL.~--Records of a notable job of sewer construction at Wilmington, Del., in 1903, are furnished by Mr. T. Chalkley Hatton. The sewer was built by day labor for the city; its cross-section at various points is shown by Fig. 265. The cross-section of sewers in trenches deep enough to cover the arch are marked "deep cutting"; the sections where the arch projects above the ground surface are marked "light cutting." The section through the marsh was 700 ft. long, the cutting being 8 ft. deep, and at high tide the marsh was flooded 1 to 4 ft. The material was a soft mud that would pull a tight rubber boot from a workman's foot. The cost of this marsh excavation including cofferdams, underdraining, pumping, etc., was $4.60 per cu. yd. For 1,100 ft. the 9¼ ft. sewer was through a cut 22 to 34 ft. deep, the material being clay underlaid by granite. A Carson-Lidgerwood cableway was used. Although the crown of the arch was but 8 ins. thick, it withstood the shock of dumping 1 cu. yd. buckets of earth and rock from heights of 3 to 10 ft.; and the weight of 25 ft. of loose filling caused no cracks in the concrete. Concrete was placed in 4-in. layers (the depth of the lagging) and well rammed, since it was found that "wet" concrete left small honeycombed spaces on the inner surface. Concrete for the invert was 1-2-6, the stone being 1½-in. and smaller, and the sand being crusher dust. The arch was 1-2-5. The reinforcing metal used in the 9½-ft. sewer was No. 6 expanded metal, 6-in. mesh, in sheets 8×5½ ft., supplied by Merritt & Co., of Philadelphia. A single layer was placed around the sewer, 2 ins. from the inner surface, its position being carefully maintained by the men ramming, and with but little difficulty as the sheets were first bent to the radius of the circle. Each sheet was lapped one mesh (6 ins.) over its neighbor at both ends and sides, and no sheets were wired except the top ones, which were liable to displacement by men walking over them. [Illustration: Fig. 265.--Cross-Sections of Sewer at Wilmington, Del.] The metal used on the rest of the work was a wire-woven fabric furnished by the Wight-Easton-Townsend Co., of New York. This fabric comes in rolls 5½ ft. wide and 100 ft. to the roll. The wire is No. 8, with a 6×4-in. mesh. This fabric was placed by first cutting the sheets to the required length to surround the sewer entirely, embedding it in the concrete as fast as concrete was placed, in the same manner as was done with the expanded metal except over the center where, on account of its pliability, the fabric was held the proper distance from the lagging by a number of 2-in. blocks which were removed as the concrete was placed. The wire cloth, being all in one sheet, can be placed a little more expeditiously than expanded metal, but, on the other hand, the expanded metal holds its position better in the concrete, since it is more rigid. We quote now from Mr. Hatton's letter: "The major portion of concrete was mixed by machine at a cost of 66 cts. per yard, including wheeling to place, coal and running of mixing machine, wages being $1.50 per day of 8 hrs, Stone was delivered alongside of machine and all material had to be wheeled in barrows upon the platform, and after mixing to the sewer. Placing and ramming concrete around the forms cost 39 cts. per cu. yd., additional. Setting forms in invert cost 2 cts. per cu. yd., setting centers 7 cts. per cu. yd. Cost of setting forms and centers includes placing steel metal. Each lineal foot of 9¼ ft. sewer contained 1 cu. yd. of concrete, although the section only calls for 0.94 cu. yd. The excess was usually wasted by falling over sides of forms or being made too thick at crown. "This yard of 1-2-5 concrete cost in place as follows (record taken as an average of several-days' run): Cement, 1.31 bbls. at $1.30 $1.703 Stone, 0.84 cu. yds. at $1.21 1.016 Stone dust, 0.42 cu. yd. at $1.21 0.508 Labor at 18¾ cts. per hour 0.987 Labor setting forms and setting metal 0.045 Cost of forms (distributed over 1,800 ft. of sewer) 0.082 40 sq. ft. expanded metal at 4¼ cts. 1.700 Labor plastering invert 0.070 ------ Cost per ft., or per cu. yd. $6.111 "The forms for the invert were made of 2-in. rough hemlock boards cut out 4 ins. less diameter than the diameter of the sewer, except for 18 ins. at the bottom of the form which coincided with the inside form of sewer. The bottom of the sewers was laid to the bottom of this form before it was set. Then the lagging, consisting of 2×6-in.×16-ft. hemlock planed, was placed against each side of the form, one at a time, and the concrete brought to the line of this top in 6-in. layers until the whole invert was finished. These forms were set in 16-ft. sections, five to each section. "The centers consisted of seven ribs of 2-in. hemlock upon which was nailed 1½-in. lagging, 2 ins. wide, tongued and grooved, and were 16 ft. long, non-collapsible, but had one wing on each side, 9 ins. wide, which could be wedged out to fit any inaccuracies in the invert. We used four of these centers setting two at each operation and worked from two ends. We left the centers in for 18 hours before drawing. "The cost of the concrete on the smaller sewers was the same as are the larger sewers, but the steel metal cost less, as it was wire woven metal that cost 2½ cts. per sq. ft. It was much easier handled and cut to no waste as it came in long rolls and was very pliable. "After training our men, which occupied about one week or 10 days, we had no difficulty in getting the concrete well placed around the metal, preserving the proper location of the latter, which, however, bore constant watching, as a careless workman would often take the temporary supporting blocks and allow the metal to rest against the wooden center, in which case the metal would show through the surface inside of the sewer. The metal was kept 2 ins. away from the inside forms and the arch. To keep it at this location we had several 2-in. wooden blocks cut which were slipped under the wire or expanded metal and as soon as some concrete was pushed under the wire at this point the block was removed. "After the forms were removed the invert needed plastering, but the arch was practically like a smoothly plastered wall except where it joined the invert, where it frequently showed the result of too much hurry in depositing the first loads of concrete on the arch. We remedied this by requiring less concrete to be deposited at the start, thus giving the rammers time to place the material properly. "An interesting result was obtained in the smoothness of the inside surface by using a mixture of different sized stones. When ¾-in. stones or smaller were used in the arch, the inside was honeycombed; but, where 1 to 1½-in. stones (nothing smaller) were used, the inside was perfectly smooth, and the same was true of the invert, showing that the use of larger stones is an advantage and secures more monolithic work. When the run of the crusher from 1½ to ¾-in. stones was used the work was not at all satisfactory. "The difference in cost of mixing by hand and machine is practically nothing on this kind of work. As the moving of the machine to keep pace with the progress of the work equals the extra cost of mixing by hand when the mixing can be done close to the point where the cement is being placed." The total cost of the sewers, including excavation, etc., was: Cost per lin. ft. 9¼-ft. sewer through marsh $32.00 9¼-ft. sewer in cut averaging 24½ ft. 24.00 6½-ft. sewer in cut averaging 12 ft. 10.00 5-ft. sewer in cut averaging 11½ ft. 6.70 ~SEWER WITH MONOLITHIC INVERT AND BLOCK ARCH.~--The following records of construction for a sewer built at Coldwater, Mich., in 1901, are given by Mr. H. V. Gifford. The sewer had a monolithic invert and a block arch. The sewer was circular, having an inner diameter of 42 ins., the thickness of the invert and the arch alike was 8 ins. Figure 266 is a cross-section. The concrete was 1 of Portland cement to 6 of gravel. There were 11 concrete blocks in the ring of the arch, each block being 24 ins. long, 8 ins. thick, 8 ins. wide on the outside of the arch and 5¾ ins. wide on the inside of the arch. A block weighed 90 lbs. which was too heavy for rapid laying; blocks 18 ins. long would have been better. Some 8,500 blocks were made. Molds were of 2-in. lumber, lined with tin, for after a little use it was found the concrete would stick to the wood when the mold was removed. The four sides of the mold formed the extrados, the intrados, and the two ends of the block; the other two sides being left open. When put together the mold was laid upon a 1-in. board, 12×30 ins., reinforced by cleats across the bottom. The sides of the molds were held together with screws or wedge clamps. When the blocks had set, the sides of the molds were removed, and the blocks were left on the 12×30-in. boards for 3 days, then piled up, being watered several times each day for a week. A gang of 14 men made the blocks; 2 screening gravel through 1-in. mesh screen; 4 mixing concrete; 4 molders; 3 shifting and watering blocks, and 1 foreman. With a little practice each molder could turn out 175 blocks a day; and since each block measured ¾ cu. ft., the output of the 14 men was 19½ cu. yds. a day. Mr. Gifford informs us that the wages were $1.50 a day for all the men, except the foreman. The daily wages of the 14 men were $22, so that the labor of making the blocks was $1.10 per cu. yd. [Illustration: Fig. 266.--Sewer with Monolithic Invert and Block Arch.] Each batch of concrete, containing ½ bbl. of Portland cement costing $1.35 per bbl., made 18 blocks. (1 bbl. per cu. yd.) Since the gravel cost nothing, except the labor of screening it, the total cost of each block was 11 to 12 cts., which includes 0.85 cent for use of molds and mold boards, which were an entire loss. At 12 cts. per block the cost was $4.32 per cu. yd. The contract price was $3 per lin. ft. of this sewer, as against a bid of $3.40 per ft. for a brick sewer. When the trenching had reached to the level of the top of the invert, two rows of stakes were driven in the bottom, stakes being 6 ft. apart in each row, and rows being a distance apart ¼-in. greater than the outer diameter of the sewer. These stakes were driven to such a grade that the top of a 2×4-in. cap or "runner" set edgewise on top of them was at the proper grade of the top of the invert. The excavation for the invert was then begun, and finished to the proper curve by the aid of a templet drawn along the 2×4-in. runners. In gravel it was impossible to hold the true curve of the invert bottom. Concrete was then placed for the invert. To hold up the sides of the invert concrete, a board served as a support for the insides, but regular forms were more satisfactory in every respect except that they were in the way of the workmen. A form was tried, its length being 6 ft. It was built like the center for an arch, except that the sheeting was omitted on the lower part of the invert. It was suspended from the cross-pieces resting on the "runners." After the concrete had been rounded in place, the form was removed and the invert trued up. This form worked well in soil that could be excavated a number of feet ahead, so that the forms could be drawn ahead instead of having to be lifted out; but in soil, where the concreting must immediately follow the excavation for the invert, the form is in the way. The invert was trued up by drawing along the runners a semi-circular templet having a radius of 21½ ins. Then a ½-in. coat of 1-2 mortar was roughly troweled on the green concrete. Another templet having a 21-in. radius was then drawn along the runners to finish the invert. When the plaster had hardened, two courses of concrete blocks were laid on each shoulder of the invert, using a 1-2-¼ mortar, the ¼ part being lime paste. The lime made the mortar more plastic and easier to trowel. Then the form for the arch was placed, and as each 8-ft. section of the arch was built, a grout of 1-1 mortar was poured over the top to fill the joints. Earth was thrown on each shoulder and tamped, and the center moved ahead. Common laborers were used for all the invert work, except the plastering which was done by masons who were paid 30 cts. per hr. Masons were also used to lay the concrete blocks in the arch. Mr. Gifford states that two masons would lay at the rate of 100 lin. ft. of arch per day, if enough invert were prepared in advance. As there were 11 blocks in the ring of the arch, this rate would be equivalent to 7½ cu. yds. of arch laid per mason per day. [Illustration: Fig. 267.--Concrete Block Manhole.] ~COST OF BLOCK MANHOLES.~--The following costs of constructing concrete block manholes for electric conduit at Rye, N. Y., were recorded by Mr. Hugh C. Baker, Jr. The arrangement of the blocks, their size and shape and the dimensions of the completed manholes are shown by Fig. 267. The blocks were molded of 1-2-5¾-in. broken stone concrete in 30 wooden molds made by a local carpenter at a cost of from $3.50 to $12 each. The concrete was placed in the molds very wet, with very little tamping, and was allowed to set for seven days before the blocks were moved to the work. The molds were left in place from 24 to 36 hours. With the facilities at hand six complete sets of top blocks were made each day by four men, when no wall blocks were being made, and half a set (15) wall blocks and two sets of top blocks were made each day by four men. The cost of the block manholes complete was as follows, per manhole: 30 wall blocks, 2½ cu. yds. $21.00 6 cover blocks, 1½ cu. yds. reinforced 4.27 I-beams for cover, in place 5.40 Supervision, freight, hauling 5.6 tons concrete 9.38 Labor placing cover, 3 hrs. at 15 cts. 0.45 Labor placing walls, 20 hrs. at 15 cts. 3.00 ------ Total, exclusive of iron cover $43.50 ~CEMENT PIPE, CONSTRUCTED IN PLACE.~--In constructing 8-in. cement sewer for the Foster Armstrong Piano Co.'s works at Rochester, N. Y., a gang of seven men averaged 300 ft. of pipe per 10-hour day, using a Ransome pipe mold. The mold is shown by Fig. 268. It is made of sheet steel, with an inner core 10 ft. long, the front end of which is surrounded with a sheet steel shell that serves as an outer form for the pipe. The mortar mixed rather dry was packed into the annular space between core and shell by one man, using a short wooden rammer. A second man kept the mold slowly moving forward by operating the lever, which by means of a ratchet and drum winds up a wire rope stretched ahead to a deadman in the trench bottom. As the mold moves ahead it leaves behind it the cement pipe. A third man carefully filled under the invert and over the haunches of the green pipe with earth to give it support. The following was the itemized cost per day, 300 ft. of pipe laid: 6 men at $1.70 per 10-hour day $10.20 1 foreman 3.00 3 bbls. cement at $1.25 3.75 3.3 cu. yds. sand at 85 cts. 2.80 Water 0.15 ------ Total for 300 lin. ft. $19.90 This is equivalent to 6.63 cts. per lin. ft. of pipe. [Illustration: Fig. 268.--Ransome Continuous Mold for Concrete Pipe Construction.] In Trans. C. E., Vol. 31, 1894, p. 153, James D. Schuyler gives the cost of cement pipe made by the Ransome system for the Denver Water Works. There is a wrought iron shell of the size of the inner diameter of the pipe forming the inner mold. To this shell is attached a "leader" and "saddle" of larger diameter forming the outer mold. These molds are drawn slowly along the trench by a cable and horse whim, and the concrete is shoveled continuously into the core space between the molds and rammed on a long incline. The top half, or arch, of the pipe is supported by sheet iron plates (2 ft. wide), placed one after another on the forward end of the mold; and, being clamped together at the top and sides, remain in position after the mold is slid out from under them. After the mold has passed along, these iron plates are supported by upright sticks and by horizontal clamping rods. The plates are left in place for 24 to 48 hrs. The concrete, made 1-3½, river sand and gravel, was machine mixed. A gang of 30 men mixed, wheeled, shoveled and tamped the concrete, attended to the plates, cleaning and greasing them, etc. This gang would make short runs at the rate of 900 lin. ft. of pipe a day, but counting stoppages, the average rate was 300 ft. a day. The inner diameter of the pipe was 38 ins., and its bottom was molded flat for a width of 18 ins. The concrete shell was 2½ to 3 ins. thick. The pipe was washed with pure cement grout, applied with brushes after removing the iron plates. With cement at $3.75 per bbl., gravel at $1.25 per cu. yd., and labor at $1.75 to $2 per day, the cost of this pipe was $1.35 to $1.50 per ft., after the gang was well organized. ~PIPE SEWER, ST. JOSEPH, MO.~--In constructing extensions to 36-in., 42-in., 48-in. and 72-in. sewers at St. Joseph, Mo., reinforced concrete pipe of the form shown by Fig. 269 was employed. The thickness of shell for the various sizes was 4 ins., 4½ ins., 5 ins., and 7 ins. All sizes were made in 3-ft. lengths, one end of which is rebated and beveled to form a spigot and the other end of which is chamfered on the inner edge to receive the bevel of the spigot. This jointing leaves a circumferential groove, into which the hooked ends of the longitudinal reinforcing bars project in such a way that a circular hoop can be threaded through them to connect successive lengths. The reinforcement is of the same form for all sizes of pipe, but seven longitudinals were used in the 72-in. size and five for all smaller sizes; the circumferential bars were in all cases spaced one 9 ins. from each end. The pipe, as described, is the standard pipe made by the Reinforced Concrete Pipe Co., of Jackson, Mich., and is covered by patents. The practice of this company is to manufacture the pipe itself on the ground and furnish it to the contractor. It does not contract to build sewers nor does it dispose of rights to manufacture to contractors. [Illustration: Fig. 269.--Jackson Concrete Sewer Pipe.] _Pipe Molding._--The pipe is molded endwise. A bottom plate so shaped as to form the hub or receiving end of the pipe is set up. On the upper or inner flange of this cast iron bottom plate is set the core defining the inside diameter of the pipe; this core is in four segments of sheet steel. The longitudinal reinforcing bars are next inserted in slots in the bottom plate and the outside form of sheet steel is then set up on the lower and outer flange of the bottom plate. Spacing clips on the top edge of the outer shell hold the tops of the reinforcing bars in position. The concrete is then shoveled into the annular mold and tamped until it reaches the level for the first circumferential reinforcing bar; this is then placed by removing the spacing clips, threading the hoop over the longitudinal bars and sliding it down to position. Filling and tamping then proceeds until the second hoop is to be placed; this is placed exactly like the first, and filling and tamping then proceeds until the mold is filled. At the St. Joseph work a 1-2-3 mixture, with crushed limestone aggregate ranging from pea size to 1-in. stone was used. The molding was done in tents which were heated by coke fires in salamanders in freezing weather. _Pipe Laying._--In laying, the pipes are handled and lowered into position just as are cast iron water pipe. Successive lengths are placed by inserting the spigot ends into the chamfered hub ends and then threading the tie hoop through the hooked ends of the projecting longitudinal reinforcing bars. A strip of galvanized iron is then passed under the pipe and bent up so as to girdle the circumferential groove except for a space at the top; the groove is then poured with a wet 1-2 cement mixture, which, when hardened, completes the joint. ~COST OF MOLDING SMALL CEMENT PIPE.~--Mr. Albert E. Wright gives the following account of the method and cost of molding and laying 6 to 12-in. cement pipe for irregular work at Irrigon, Ore.: The pipe was 6 to 12 ins. inside, made of Portland cement and clean, sharp sand of all sizes up to very coarse. The mortar was mixed rather dry, but very thoroughly, using 14.1 cu. ft. of sand to 1 bbl. of cement, or very closely a 1 to 4 mixture. From six to seven buckets of water were used to each barrel of cement, except for the 6-in. pipe, for which the mortar had to be made somewhat stiffer in order to remove the inner form, which was not made collapsible as in the larger sizes. The forms were sheet iron cylinders with a longitudinal lap joint that could be expanded after molding the pipe, and removed without injuring the soft mortar. The inner form was self-centering, so that there was little variation in the thickness of the pipe. Four men were required in making cement pipe by hand; one mixed the mortar, and wheeled it to the place of work; another threw it into the form a little at a time with a hand scoop; a third rammed it with a tamping iron, and a fourth kept the new pipe sprinkled, and applied a coat of neat cement slurry to the inside when it was sufficiently hard. In molding, the form of the bell at the bottom was secured by an iron ring that was first dropped into the form, and the reverse or convex form at the top was made with a second ring. While still in its form the pipe was rolled or lifted into its place in the drying yard, and the form was then carefully removed. A very slight blow in removing the form would destroy the pipe, and a considerable number, especially of the larger sizes, collapsed in this way, and had to be remolded. To avoid handling, the pipe was stacked on end a few feet from the place of mixing, the form being moved as the yard filled with pipe. One crew of four men could make about 250 joints or 500 lin. ft. of pipe a day. As soon as hard enough, the pipe was turned end for end, and was then kept wet for several weeks before being laid. The coating of neat cement on the inside was applied with a short whitewash brush, and was a small item in the cost. In laying, the trench was carefully finished to grade in order to have the joints close nicely, and the ends were well wet with a brush. The mason then spread mortar, mixed 1 to 2, on the end of the pipe, and laid a bed of mortar at the bottom of the joint. He then jammed the section into place, and swabbed out the inside of the joint with a stiff brush, to insure a smooth passage for the water. A band or ring of mortar was spread round the outside of the joint as an additional reinforcement. One barrel of cement would joint about 300 sections of pipe. The materials cost as follows: Portland cement, per bbl., $4.45; labor, per day, $2; foremen, per day. $2.50 to $3; hauling, per load mile (1 cu. yd.), 20 cts.; sand, free at pit; water, free. The pipe was all of a 1-4 sand and cement mortar, and the amount of cement in one foot of pipe was arrived at by assuming that where the sand has voids in excess of the cement used, the mortar will occupy 1.1 (see Chapter II) times the space of the dry sand, which yields the following formula: Where-- c = cost per bbl. of cement, or $4.45. n = cu. ft. in one bbl. (taken at 3.5 here). s = ratio of sand to cement, or 4. d = inside diameter in inches. t = thickness of pipe in inches. l = length of pipe considered, or 1 ft. here. Then: c × l × [pi] × (dt + t²) Cement-cost per foot = --------------------------, n × s × 1.1 × 144 which gives here = 4.45 × 1 × 3.142(dt + t²) ------------------------------- = 0.00631(dt + t²). 3.5 × 4 × 1.1 × 144 This gave the following cement costs per lineal foot: Diameter, Thickness, Cost ins. ins. per foot. 6 1¼ $0.0571 8 1¼ 0.0730 10 1-3/8 0.0998 12 1½ 0.1278 The sand cost was based on 15 cts. per cubic yard for loading, and a haul of two miles of 1 cu. yd. to the load, making five trips per day, at $4 for man and team. It bears a constant ratio to cement cost, being 11.2 per cent. of the cement cost. The labor cost of making was based on the foreman's estimate that a foreman, tamper, mortar mixer, and water man should finish 250 joints a day of 6 or 8-in. pipe. For the 10 and 12-in. pipe, the labor was assumed to be greater in proportion to the material. The foreman was taken at $3, one man at $2.50 and two at $2. The cement for painting the inside was neglected. Hauling the pipe to place was taken at twice the cost of hauling the sand per mile, and a haul of 4 miles was assumed. The cost of laying was based on a foreman's estimate of 2 cts. per foot for trench, and that one man to lay, one man to plaster the joints, one helper and one man to back-fill would lay 600 ft. per day of 6 or 8-in. pipe. The larger sizes were assumed to cost more in proportion to their material. These various costs gave the following results for small size pipe: --Cost per foot for-- 6-in. 8-in. 10-in. 12-in. pipe. pipe. pipe. pipe. Cement $0.057 $0.073 $0.099 $0.128 Sand 0.006 0.008 0.011 0.014 Labor 0.019 0.019 0.026 0.034 Hauling 0.024 0.032 0.044 0.056 Laying 0.024 0.024 0.032 0.042 Trench 0.020 0.020 0.020 0.020 ------ ------ ------ ------ Totals. $0.15 $0.176 $0.232 $0.294 The above costs show that the pipe in place costs about twice as much as pipe in the yard, even with cement at $4.45. [Illustration: Fig. 270.--Bordenave Pipe for Swansea, England, Water Works.] ~MOLDED PIPE WATER MAIN, SWANSEA, ENGLAND.~--As a good example of foreign practice in molded pipe conduit work a water main constructed at Swansea, England, has been selected. This pipe line had to operate under a head of 185 ft.; it was constructed under the patents of the French engineer, Mr. R. Bordenave, who has built many miles of the same type of conduit on the Continent. Fig. 270 shows the construction of the pipe, the drawing being a part longitudinal section through the shell at the joint. The pipe consists of an inner and an outer reinforcement separated by a sheet steel tube and all embedded in a 1-2 mortar. Both inner and outer reinforcements consists of longitudinal bins of cruciform (+) section wound by a spiral bar of the same section wired to them at every intersection. Only the outer reinforcement and the steel tube are considered in calculating the strength of the pipe, the inner reinforcement being considered as simply supporting the mortar. _Fabrication of Reinforcement_.--The steel tube is made of 1 mm. (0.04 in.) thick sheets of steel bent to a cylinder and jointed longitudinally by welded butt joints, welded by a blow pipe using acetylene and oxygen. Tests of this welded joint by R. H. Wyrill, Waterworks Engineer, Swansea, showed it to be quite as strong as the unwelded steel cut from the shell. The circumferential joints of the tube were made by turning up the edges of the sheets and welding them; this gives a flexible watertight joint. The tube was made in lengths of 9 ft. 9½ ins. and its ends were turned up all around; just back from the turned-up ends a vertical sheet steel collar was welded to the tube to form a strip end for the external coating. These details are shown in Fig. 270. When the tube for a length of pipe is completed the inside shell reinforcement previously made is slipped into it and the outside shell reinforcement is formed on it as a mandril, as shown by Fig. 271. [Illustration: Fig. 271.--Applying External Reinforcement to Bordenave Pipe.] [Illustration: Fig. 272.--Casting Bordenave Pipe at Swansea, England.] _Molding._--When the three positions of the steel skeleton were completed, as shown by Fig. 271, they were set on curved wooden curbs made to the exact shape necessary to center them and preserve the correct thickness of cement coating. A collapsible core was lowered into position in the inside, and a two-part sheet steel mold was erected outside; the space between core and mold was then poured with a thin mortar of one part Portland cement to two parts clean river sand. During the process of pouring, the outer steel mold is sharply struck with wooden mallets to facilitate the escape of air bubbles. The mortar was mixed on an elevated traveling platform which is shown in Fig. 272, which also shows a completed pipe, a core being withdrawn, a filled mold and a section of reinforcement set up. The difficult feature of the molding process was found to be the determination of the time for withdrawing the core and removing the exterior mold; the time of setting of the mortar was different in warm and in cool weather and varied with the wetness of the mixture, the brand of cement, etc. By using a single brand of cement that ran very uniform in quality and time of setting it was possible, however, for the workmen, after a little practice, to gage very accurately the correct time for removing the molds. With four sets of molds a gang of eight men would curb 16 pipes per day under favorable conditions, but when the temperature was low it was not possible to make more than six or eight pipes. The pipes were allowed to stand four or five days after the removal of the mold; they could then be removed by a crane and laid in stock until used. It was found advisable to let the pipes age about four weeks before laying; by this time, it is stated, they would stand as much rough usage as cast iron pipe. _Laying_.--The pipes were laid much in the same way as cast-iron pipes are laid; they were each 9 ft. 9½ ins. long and weighed each about 12 cwt., and were handled by ordinary tackle. In laying, the pipes were adjusted end to end and the joint enclosed by a temporary steel ring inside which the bitumen seal, Fig. 270, was run and allowed to set when the steel ring was removed. The joint was then encircled by a collar of similar construction to the pipe itself and the space between collar and pipe was poured with cement mortar. About ten lengths of pipe were laid per day by one gang of men, one jointer and his assistant making all the cement and bitumen joints as fast as the gang could lay the pipes.