Superintendent Saved City Some $68,000 by Cutting Water Supply Tunnel in Rock
The following is a description by Alexander Milne, superintendent of the St. Catharines, Out., water works, of the construction of a water supply tunnel through a solid rock strata, by means of which the department was saved some $68,000 in comparison with another proposed plan using a rock cut:
Prior to 1912, the city of St. Catharines was supplied by one 20-inch main to the reservoir three miles out from the city. At that time the supply became entirely too short for proper fire protection. I was instructed to make the necessary surveys and prepare plans for duplicating mains, for which I recommended 36-inch, but it was cut down by the board to 24-inch later on. In making the surveys prior to that, the original main came from the same reservoir that now supplies the secondary main, but came at the western end of the city, leaving the whole bridge system supplied in that form, the result being that the eastern end of the city received very insufficient pressure, both for fire protection and the domestic use.
We decided to cross the whole construction at right angles to provide adequate fire supplies for the northern or domestic part of the city. Our reservoir comprises an area of 115 acres with a storage capacity of 365,000,000 gallons, with a continuous feed under direct control. We can pump 30,000,000 gallons per day. Route No. 1 was the original route for the first pipe, going to the city on the county highway, to form a continuation of the same route, and then had a grade line from the reservoir; it was necessary to follow to this point the old route, then this crossed under the pipe line of the Hamilton Traction Company, continuing on through to a point where section A terminated. I might say that in making the survey and the plans for it, we divided the system into three sections, A, B and C, A being the reservoir section, B being 18,000 feet of country line through farms, and C being the city section. A and B were awarded to contractors. In getting this route, we ran through very rugged rock, with a maximum cut at one point of 37 feet. We cut in rock all the way through to this point with very heavy timber. The reservoir elevation was at 300 feet coming into a ravine and then down the mountain side and we ran into this condition all the way through to the elevated section. The estimated cost of that was about $128,000.
I was practically “scared stiff” for fear the board would accept No. 1 as the definite route, because I never had tackled anything in construction work and that would put me in an awkward position to get material in and do the work. Going over that carefully, we ran a couple of other trial routes at this point, pumping from the reservoir to the second reservoir which would have necessitated about 47 feet rock cut.
A study of the rock situation was then made throughout the entire area for about three miles, which is almost uniform from this point, where we had a drop of eighty-six feet and a secondary drop of fifty-six feet, known as Lageo Falls. We found a strata of rock there that extended clear around the whole route leading for miles in the other direction. We investigated that to see whether there were any signs of seepage from the upper strata carrying ground water and found none. My consulting engineer, after locating all the phases of it possible, suggested one day, “Why not cut a tunnel through there and take the direct line?” We gave the matter considerable thought and, putting a diamond drill on the job, ran a series of test holes which were afterwards developed into six-inch openings for air vents. We found the stratification uniform, and recommended the adoption of the tunnel scheme, not thinking but that we would have to lay the pipe in the tunnel. Over somewhat different ground from profile No. 1, we found this condition to the same point on the north side of the line extending to some point at the end of section A. The position of the rocks is an almost vertical drop to that point and then on down.
Ultimately we developed a tunnel along that line, carried a 36-inch main to this point and developed a shaft through the tunnel, using the section for a spill bank. We developed a shaft 5 feet square, and at this end put a bulkhead with a 30-inch valve for a blowout by feed from the other main. The stratification of that rock varied from 6 1/2 to 8 feet, vertically, and we excavated from that only enough to allow the swing of the drill which, with the break of the rock gave an average of about 6 feet. On excavating that, we found between the two stratas of rocks, a strata of lime. We decided to place another bulkhead there, this section being in open country enclosed with a concrete arch in that form. Water was turned into the tunnel on the 13th of August, 1913, and we developed a slight leakage at this point through openings in the rock where the first blasting came. These have all closed up and today that tunnel does not show any leakage at either end. When the valve is shut at this point and water turned in, the flow in the venturimeter is absolutely nil: there is no pipe laid through it. Our saving amounted to about $68,000 as compared to No. 1. down the mountainside.
—From a discussion before the annual convention of the American Water Works Association.