TWIN RESERVOIRS AT BROCKTON, MASS.
Concerning the recent improvements of the water system at Brockton. Mass., City Engineer Charles R. Felton shows the general location and design of the completed twin reservoirs, with a brief resume of the reasons leading up to their construction, and a brief description of them as completed : Their construction was brought about by the necessity for greater storage capacity, precipitated by the rejection of the Montello standpipe, but which would shortly have been required even with that one still in commission. The pressure on the street on Prospect Hill was often less than 20 pounds under the old conditions, and at times of greater consumption lower still. The greatest height that the water could reach under former conditions was elevation 253 feet above mean low water. The tops of the present reservoirs are 288.5 feet above mean low water, giving a maximum pressure in the centre of the city of 15 pounds more than under the old conditions. This, however, does not represent the actual advantage in pressure, as the average and minimum pressures are greater. The amount of storage required was, to a certain extent, a matter of opinion, but it was thought advisable to provide for at least one day’s consumption under the worst conditions at a future time about equal to the limit of the present Silver Lake supply. As an average consumption of two and one-half million gallons necessitates the provision of about four and one-half million gallons of water, it was predicted that an average of four million gallons per day, which is the estimated capacity of the Silver Lake source, would require in the vicinity of eight million gallons on certain days, and this amount of storage was accordingly provided. On account of the possibility of trouble with vegetable organisms in the water, necessitating cleaning or possible treatment, it was deemed necessary to provide two compartments. It was at first thought best to construct a reservoir of earth embankment and core-wall, with a dividing wall, but on further consideration it appeared to be better to construct an all masonry reservoir at substantially the same cost under our conditions, and in our opinion more easily cleaned and of more sightly appearance. Still further consideration of the matter convinced us that two entirely separate reservoirs of this type would be cheaper than one large one with a division wall. Having decided upon the method of construction, a location situated about 5,500 feet from the present system was selected and connection made therewith by a 30-inch main. This system is susceptible of indefinite expansion by the addition of further reservoirs on the surrounding land, which is of ample area for any probable future needs, • and by the duplication of the 30-inch main. Provision has been made for covering one of the reservoirs, should it become necessary. The Act enabling the Water Commissioners to seize land, was passed by the Legislature on Feb. 15th, 1911. A loan was authorized on Feb. 27th; takings were made by the City Council on March 9th; ground was broken for the reservoirs on March 28th; the first reservoir was completed on Aug. 7th; and the second on Oct. 4th. The work was done entirely by city labor, under the direction of your Superintendent of Waterworks,—Mr. Horace Kingman—and was accomplished without serious accident to property or employee. The reservoirs are of concrete, reinforced with plain round bars, except for a few twisted bars where the sides and bottom join. The concrete is of very rich mixture, to render it impermeable, the bottom courses being 1 cement, 1 sand, and 2 stone, to a height of ten feet, with a 1,1/4, 3 mixture above this point; both mixtures containing hydrated lime in the proportion of 5 per cent, of the cement by weight. The walls are 30 inches thick at the bottom and 15 inches at the coping course, which is 19 inches square. The floor layer consists of two courses of concrete, 6 inches thick; the lower one of 1, 2, 4 concrete, and the upper one 1, 1½, 3 concrete reinforced with a 54-inch bar 1 foot apart in both directions. The horizontal reinforcement consists of plain round bars from 1¼ inches in diameter at the bottom to 5-8 inch in the coping. The maximum strain upon the metal, considering the stresses as applied to a cylinder 160 feet in diameter, are 13.000 pounds to the square inch, with the reservoirs overflowing, or 12,000 pounds at the proposed high water mark, 18 inches below the top. Vertical, square twisted rods ⅝ inch in diameter and 1 foot apart, were introduced into the foundation and also bent into the floor. These rods were extended to the top of the reservoir, but spaced two feet apart after the first thret courses. The bottom was also connected with the foundation by ⅜ inch twisted rods. All these rods were purchased under the specifications for reinforcing steel, adopted by the Association of Steel Manufacturers, the main requirements of which are as follows:
Phosphorus, maximum. Bessemer, Open-Hearth, .10; Ultimate Tensile Strength, pounds per square inch, 55 70,000; Yield point, minimum, pounds per square inch, 33,000; Elongation, per cent., 1,400,000: in 8 inches, minimum, T. S. Cold bend without fracture: Bars under inch in diameter or thickness, 180°d.=It; bars 3/4 inch in diameter or thickness and over, 180°d.=lt.
Dragon cement was used exclusively on the work, and the specifications were those of the American Society for Testing Materials. One sample at least was taken from every car. and an average of 55 samples resulted as follows:—each sample being a composite from several bags:
Sand and gravel were obtained from a large hill three miles distant from the location, and were very expensive, both on account of the length ol haul and the large amount of material handled to get stone, about 1-5 of the total being stone of the required size, viz.: that which would pass all-3 inch screen. The screen was of the revolving type, run by a gasolene engine, and under ordinary conditions would pass about 175 yards of material in eight hours. The resulting product was excellently graded. The greatest care was taken to make the concrete impermeable. an entire course being run when once started. These courses were 30 inches in height, except the bottom one, which was 36 inches and contained about 110 cubic yards. No departure from this plan was found necessary, the concrete being placed continuously in courses 6 inches thick, from three and one-half to six hours being consumed on a 30 inch course. After the concrete had partially set, usually in about 7 hours, it was thoroughly scraped with wire brushes and kept wet until the next course was ready, usually covered with wet bagging and carefully swept just before placing. A steel dam, 4 inches by 3-8 inch, was embedded 2 inches deep in the top of each course, and about I foot from the inside of the reservoir. This dam was lapped and bolted with five 3/4 inch bolts, and figured in the design for its full tensile value as metal. In addition to the dam a triangular groove about 1-5 inch deep was placed in the top of each course. Before beginning a new course the joint was washed with neat cement grout. No waterproofing or washing of the surface was required or allowed, and less than a quart of cement was required to remedy any defects of appearance.
The plant consisted of an elevated tank of 5,000 gallons capacity, into which water was pumped by gasolene engine a distance of about 1,300 feet. Two Smith concrete mixers, set at an elevation corresponding substantially in level to the top of the reservoirs and operated by 15 H. P. electric motors connected with 6,600 volt electric line which happened to cross the lot, with voltage stepped down to 550. The mixers were fitted with side charging apparatus, and the material elevated to the mixers. The concrete was placed, usually, at the rate of from 24 to 30 cubic yards per hour with ordinary wheelbarrows, the greatest care being taken to have the material thoroughly tamped. The labor was all paid at the city rate of $2.50 per day of eight hours; carpenters $4.80 per day; foreman $5.00 per day; masons 72c. per hour; teams $5.50 per day of eigilt hours. One of the greatest obstacles in accomplishing work of this character economically is the difficulty of employing all the labor to advantage between pourings, especially when it is necessary to conform to the present drastic eighthour laws. The total cost of the reservoirs exclusive of the engineering was almost exactly $80,000.00, or about one cent per gallon. The cost of the engineering and inspection, not including my own time, was about $2,200.00.
The results have been such as to warrant the belief that no mistake was made in selecting this type of reservoir. The leakage has been confined strictly to the bolt holes, there being absolutely no leakage through the concrete or at the joints. The leakage at the bolt holes has consisted of slight seepage or damp spots which have practically closed up at this date. As a test of the amount of leakage the largest leak which could be found was piped and carefully measured from time to time. This leak at the beginning was at the rate of about three pints in twenty-four hours, which gradually decreased to less than onetenth of a pint in twenty-four hours. There is at present no leak which reaches the ground. The appearance of the reservoirs is well shown in the accompanying photographs. In a general way it may be said that the advantages of these reservoirs are as follows :
1st. An insurance against actual loss of water to the city under any probable combination of circumstances.
2nd. A valuable auxiliary fire supply under conflagration conditions,—that is, a supply and pressure capable of taking care of any ordinary fire in a large portion of the city in case the entire engine resources were required elsewhere.
3rd. A primary supply for simple hose apparatus over a considerable portion of the city.
4th. An ample domestic supply for some portions of the city not amply provided for before.
5th. A general elimination of the various doubts and considerations of remote contingencies tending to affect insurance rates, which ought to result in a general reduction in the rates in this city.
Leadville, Colo., has contracted with the American-La France Fire Engine Co., for one of their No. 10 combination chemical and hose cars.
Salt Lake City, Utah, has awarded contract to the American-La France Fire Engine Co., of Elmira, N. Y., for an auto combination chemical and hose wagon. The engine is six cylinder.
Montclair, N. J., has awarded contract to the American-La France Fire Engine Co., of Elmira, N. Y., for one of their “type 12” combination pumping engines and hose motor cars, and also one of the’ir auto city service hook and ladder trucks.