At the bottom of each hole in marsh land a wooden footing 3 feet × 6 inches × 24 inches was laid flat beneath the leg of the tower, and then the hole was filled to within 21⁄2 feet of the surface with the excavated material. Next above this filling comes a galvanized iron gutter-pipe, four inches in diameter, and filled with cement about the leg of the tower for a length of two feet. Outside of this pipe the hole is made rounding full of cement grouting.
Fig. 101.—Transmission Line at Welland Canal.
At some points along the transmission line exceptionally high towers are necessary, a notable instance being found at the crossing over the Welland Canal, where the lowest part of each span must not be less than 150 feet above the water. For this crossing two towers 135 feet high above ground are used, as seen in [Fig. 101]. Each of these towers is designed to carry all four of the three-phase power circuits that are eventually to be erected between Niagara Falls and Toronto. For this purpose there was used a special design of tower with a width of about 48 feet at right angles to the direction of the line below the top truss, and a width of about 68.5 feet at that truss where the two lower conductors of each circuit are attached.
With all spans longer than 400 feet, a tower of heavier construction than the standard type is used, and this tower provides three insulators for the support of each conductor. A tower of this type that supports the lowest conductors about 40 feet above the ground level has its corner bars made up of 4″ × 4″ × 3⁄8″ and 4″ × 4″ × 5⁄16″ L sections, has three cross-arms of extra heavy 4-inch pipe, and a 6-inch vertical standard pipe to support each group of three insulators for the highest conductor of each circuit. Each of the lower conductors of a circuit on this tower is supported by an insulator on each of the three parallel cross-arms. On some of these towers, for long spans, the two outside insulators for the support of each conductor are set a little lower than the insulator between them.
Fig. 102.—Heavy Tower at Credit River.
Fig. 103.—Angle Tower Near Bronte.