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 -in. greater than the outer diameter of the sewer. These stakes were driven to such a grade that the top of a 24-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 24-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 21 ins. Then a -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- mortar, the 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 7 cu. yds. of arch laid per mason per day.
[Ill.u.s.tration: 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 1-2-5-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, 2 cu. yds. $21.00 6 cover blocks, 1 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 sh.e.l.l that serves as an outer form for the pipe. The mortar mixed rather dry was packed into the annular s.p.a.ce between core and sh.e.l.l 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.
[Ill.u.s.tration: 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 sh.e.l.l of the size of the inner diameter of the pipe forming the inner mold. To this sh.e.l.l 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 s.p.a.ce 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 pa.s.sed 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 1-3, 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 sh.e.l.l was 2 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 sh.e.l.l for the various sizes was 4 ins., 4 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 circ.u.mferential 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 circ.u.mferential bars were in all cases s.p.a.ced 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.
[Ill.u.s.tration: 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 f.l.a.n.g.e 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 f.l.a.n.g.e of the bottom plate. s.p.a.cing clips on the top edge of the outer sh.e.l.l 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 circ.u.mferential reinforcing bar; this is then placed by removing the s.p.a.cing 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 c.o.ke 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 pa.s.sed under the pipe and bent up so as to girdle the circ.u.mferential groove except for a s.p.a.ce 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 coa.r.s.e. 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 pa.s.sage 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 a.s.suming that where the sand has voids in excess of the cement used, the mortar will occupy 1.1 (see Chapter II) times the s.p.a.ce 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 + t) Cement-cost per foot = --------------------------, n s 1.1 144
which gives here =
4.45 1 3.142(dt + t) ------------------------------- = 0.00631(dt + t).
3.5 4 1.1 144
This gave the following cement costs per lineal foot:
Diameter, Thickness, Cost ins. ins. per foot.
6 1 $0.0571 8 1 0.0730 10 1-3/8 0.0998 12 1 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 a.s.sumed 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 a.s.sumed. 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 a.s.sumed 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.
[Ill.u.s.tration: 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 sh.e.l.l 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 b.u.t.t 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 sh.e.l.l. The circ.u.mferential 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. 9 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 sh.e.l.l reinforcement previously made is slipped into it and the outside sh.e.l.l reinforcement is formed on it as a mandril, as shown by Fig. 271.
[Ill.u.s.tration: Fig. 271.--Applying External Reinforcement to Bordenave Pipe.]
[Ill.u.s.tration: Fig. 272.--Casting Bordenave Pipe at Swansea, England.]