Tips & News - April 2012

Jackingup a 500kV tower.

Once driven in, workers cut off the piles horizontally at the precise elevation that would allow for the installation of the beams — without requiring us to change the elevation of the tower. Once the I-beams were welded in place, they had to be perfectly horizontal and all the I-beams under each tower had to be at exactly the same elevation. To do this, one of our technicians used a laser level. (We ended up raising the towers a bit — about half of a 3⁄4-inch bolt hole. That was just enough room to wiggle the bolts out.) Hydro One also hired a welder to weld the I-beams across the piles perpendicular to the direction of the line. These beams became the platform for the first set of temporary I-beams that were placed parallel to the direction of the line and used as a base to jack up the towers. Then, workers cut the top part of the grillage off below grade (the rest was left in place) and, permanent support beams were slid in, under the tower, and welded in place. The tower was then lowered onto the new beams and the guy wires were re-tensioned.

We did not have to do much excavating during the project, nor did we want to. At that site, once you dig a hole, it fills with water. We were lucky at a couple of locations: We dug about 2 feet and there was not too much water coming in. It was the welder who suffered the most. He had to lie on his back — in the hole — to weld the beams to the piles after grinding the galvanizing off of the piles. All work was complete by August 2009, and we have not had any more problems with frost heave at those sites. Documenting the Work This project was carefully documented. The engineers determined and recorded all the weights and tensions for the work and then we created a job document – a step-by-step guide of what we were going to do. When the work started, a Work Methods Technician came out to the site to document the work on the first structure. We now have a well documented job procedure ready for the next person who — 20 years from now — has to do the same thing.

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