Design and methods of construction of stand-by tanks in High Park, Toronto – After detritus is settled only very dilute water passes into Lake Ontario
By: W.G. Cameron, District Engineer, Sewer Section, Department of Works, Toronto
The West Toronto stand-by tanks are situated at the southwest corner of Keele and Bloor Streets in High Park. The site, which is the lowest ground in this neighborhood, is the bed of a small creek which crosses Keele Street immediately south of Bloor. The creek is nearly dry except for storm and spring flood water. Keele Street is filled in across this creek and is about 15 feet above the level of the present top of the tanks. A culvert is provided where the fill was made, and now discharges into the storm water outlet. The site was covered with small trees and scrub and in places was wet and boggy.
Purpose. — The object of the tanks is to provide a temporary storage for flood and storm water. If the volume of water is not too great for the capacity of the tanks, it is discharged gradually into the 18-inch sewer under the large storm water outlet, and carried eventually to the disposal works at Morley Avenue. In this way, the 18-inch sewer is not overtaxed. If, on the other hand, the volume of water is too great for the capacity of the tanks, the water is discharged over weirs into the large storm water outlet. But the tanks provide a temporary resting place where the detritus, etc., may settle, and, when the storm has subsided, may be drawn off in the 18-inch sewer, while only the very dilute water from the surface passes directly to the lake without being treated.
Inlets. — The inlet sewers were all built before the tanks were constructed, so the tanks formed the missing link in the system. There were three of these inlets, one from the west (“A” on Plan, page 115), one from the east (B) along Bloor Street, and one from the north (C) along Keele Street. C is a 7′ 6″ x 8′ o” concrete culvert, into which flows a 9′ 3″ circular sewer. The sewer from the west enters the tanks at the north end of the west side as a 6′ 9″ X 5′ culvert. The sewerage flows into a channel across the north end of the tanks, contained on the one side by the north wall of the tanks, and on the other by a weir. By means of this weir, the dry flow is guided into a small 2′ x 2′ 2″ culvert, which discharges into an existing 3-ft. sewer down Keele Street. The storm water passes over the weir into the tanks. If, at some future time, the 3-ft. sewer down Keele Street be overcharged, a 12-in. pipe sewer is provided, and, by opening a valve at the weir, the surplus can be drawn off through it into the 18-in. pipe under the storm water outlet.
The sewer from the east (B), 2′ 6″ x 3′ 9″, egg shaped, enters the east side north of the centre. This sewer does not really empty into the tanks proper, but into the upper part of the storm water outlet. Even here, it is only overflow storm water that is discharged. The dry flow discharges into the 3-ft. sewer down Keele Street over which this Bloor east sewer passes.
The sewer from the north (C) enters the tanks at the east end of the north side. One hundred and seventy-three feet north of the tanks a weir is provided in this sewer, bv which the dry flow is diverted into a 24-in. tile pipe sewer (D) leading directly into the end of the 3-ft. sewer down Keele Street. This 24-in. pipe also has an overflow provided, in case at any time the 3-ft. sewer should be
overcharged and back up into the 24-in. pipe. This overflow leads indirectly into the i8-in. sewer under the large outlet. The storm water from the north flows over the weir in C, 173 ft. north of the tanks, and into the tanks. Thus we see that the dry flow from all these inlets does not reach the tanks, but all discharges into the 3-ft. sewer down Keele Street on its way to the disposal works, while only the storm water finds its way into the tanks.
Design. — The tanks are rectangular in shape, and approximately 104′ x 112′. On the north side, there channel 3.5 ft. deep for the Bloor West sewer, separated from the tanks by a weir. This has been described above. On the east side, there is a section 4 ft. deep, separated from the tanks by a weir, and from the storm water outlet by another weir. Into the north end of this section the storm water from the Keele Street sewer flows. The bottom of this section is graded back towards the north end and a gate valve is provided which can be opened to allow the section to drain into the storm water outlet. The tanks proper are divided into three parts, 17 1/2 ft. deep, by two weirs. These three divisions are graded towards the east side, where they drain into an open 18-in. sludge channel, which runs south along the inner side of the east wall and into the 18-in. tile sewer under the storm water outlet. A gate valve is provided at the end of the sludge channel at the south wall.
Eight rows of columns were used in the tanks for the support of the roof. These columns were 18 ins. square in section, 12 ft. apart centre to centre in the rows and 12-ft. centres between the rows. Two rows of columns are in each tank, and one was used as support for each of the two dividing weirs. The tanks were built of all reinforced 1:2:4 concrete. The walls were 12 ins. wide at the top, while the sides had a batter 1 in 7.6. The width at the bottom varied as the height. There was a footing provided 2 ft. deep and 12 ft. 6 in. wide. The reinforcing for the walls was 1-in. square twisted rods on the outside and 0.30 sq. in. mesh on the inside. The columns were reinforced with 1 1/8 sq. in. twisted rods, 2 ft. 6 in. long, as dowels into the footing, one 1 1/8 sq. in. rod in each corner, the full height of the column, and 3/8 in. round hoops, spaced vertically 12 in. apart. The roof slab was 6 in. thick, reinforced with 0.5 sq. in. mesh.
The girders and beams for the support of the roof slab were 24″ x 16″ and 21″ x 16″ respectively. They were reinforced with 1 sq. in. twisted rods and 3/4 in. square twisted rods, respectively. The weir walls between the tanks were 8 1/2 ft. high, 9 in. wide at the top, and 18 in. wide at the bottom, reinforced with 3/4 sq. in. bars.
The Tanks in Action. — During a storm, the water from the north and west passes over weirs and into the tanks proper, filling the three divisions successively. When all three and section F are full, the water flows back over the weir into the storm water outlet. But this will happen only during a heavy storm, and then only when the storm is at its height. Therefore, the water passing out through the storm water outlet will be practically pure storm water.
In each of the three tanks there is a floating arm situated at the east wall, which floats on the surface of the water and collects any floating material and carries it into the 18-in. pipe under the storm water outlet. When the storm has subsided the tanks are drained, gradually, through the sludge channel into the 18-in. pipe. There is a water connection provided at the west end of each tank so that the tank may be flushed clean after it has been in use.
Construction. — The ground on which the tanks were built was composed of sand on the surface, which, in small areas, formed pockets. The sub-soil was hard, blue clay. Trenches were excavated by hand for the west wall and the western third of the north wall. This part was built first because the ground was low at this side. When these walls were built, and the concrete sufficiently hardened,
they were used as a retaining wall for the next material excavated. This material was taken from inside the lines of the future tanks and next the west wall. Enough material was taken out to allow for the erection of a portion of the tanks on the west side. This portion was completed floor, columns, weirs and roof and allowed to harden. The next material excavated was then deposited on the roof of this finished portion. Thus the excavation and construction proceeded alternately from the west. A clam shell was used for excavating in the body of the tanks, but the clay was so hard that the most of it had to be loosened with picks before it could be gathered up by the clam.
The concrete was all mixed by a drum mixer very conveniently placed at the top of the bank on Keele Street. The concrete was dumped into a chute which carried it down the bank to a funnel shaped box. This box was provided with a slat which slid up and down so that concrete could be taken away in any quantity desired. The concrete was carried in concrete barrows along runways so built that they might be easily taken down and erected quickly again wherever they were required. The forms used for the concrete were all of the panel type. They were built near the work and the same sections used several times. They were made before the work was begun and grouped according to size, so that when they were needed they could be easily found and quickly erected, fastened together with bolts.
When the work on the tanks was completed the soil which had been excavated, and soil brought from other work, was spread over the top of the tanks to a depth of four feet. The bank on Keele Street was extended and neatly graded, and an easy slope was made from Bloor Street. The ground over the tanks and the slopes will probably be sodded and planted and possibly tennis courts,
etc., arranged on it, making in all a very great improvement to this corner of High Park.
Costs. — The costs in hours’ labor of this work, as kept by S. K. Ireland, B.Sc, resident engineer, are as follows : —
- Excavation. — 7,000 cu. yds., 10,472 hours, or 1.496 hours per cu. yd.
- Placing Steel. — 102 tons, 1,471 hours, or 14.4 hours per ton. (85 tons of this were bars and 17 tons mesh.)
- Building and Erecting Forms. — 52,899 sq. ft. took 8,452 hours, or 0.159 hours per sq. ft.
- Removing sq. ft. Forms. — 0.0202 hours per sq. ft.
- Mixing and Placing Concrete. — 2,522 cu. yds. took 6,394 hours, or 2.53 hours per sq. yd.
- Foreman, 1,658 hours; engineer, 1,098 hours; fireman, 1,133 hours; team, 107 hours: single horse, 451 hours.
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