How many people wonder about the inside of a hydroelectric dam? Admittedly, not many. However, like most useful machines, the inside of a hydroelectric dam will eventually wear out what with all that water rushing through it. So some specialists and, of course, the dam owners are very interested in the internals.
This is the story of how laser scanning has changed the refurbishment of just one of the more than 1750 hydroelectric plants in the United States.
The insides of a major installation can appear to be part of a dystopian science fiction movie. This sample image shows the spillway of a large hydroelectric dam. (This is an example. US government regulations and privacy agreements prevent the use of any identifying data or images.)
In operation, the spillway is lined with a continuous skin of steel plates, which of course must be replaced from time to time due to the erosive and corrosive effects of the water rushing through. Replacing the steel plating is a massive and tricky project.
Here’s how 3D Imaging Services cut costs and reduced risks in this difficult project.
The contractor recognized the need for highly accurate measurements so that the project would not suffer delays and overruns. The contractor first built a coffer dam around the entry point of the spillway. Next, the spillway was drained, and the old steel plating removed. All damage to the underlying concrete was repaired.
The new plates had to be fabricated to exactly conform to the complex shape of the concrete. Difficult enough given the curving, sloping surfaces. And the attachment mechanism to connect the plates to the concrete had to meet particular specifications. The fabricators – located many miles from the dam – would cut holes in the steel plates as they were manufactured; then, on site, each plate would be held in place temporarily while the installers drilled through the holes in the plates into the concrete. Special steel rods would be driven through the holes into the concrete and welded to the steel plates. But this method comes with a difficult specification: the holes cut into the concrete must not cut into the underlying rebar. Here is how this problem was solved.
First, a team of Ground Penetrating Radar (GPR) technicians mapped all the rebar in the spillway. They painted red markings on the concrete to show the location of all underlying rebar. Next, 3D Imaging Services used laser scanning to create an exact CAD model of the interior of the spillway. (The developed model was a wire-frame mesh.) And the model included the locations of all of the rebar markings.
The model was also aligned with the coordinate system for the project. This enhanced model was delivered to the fabricators so they could form the plates and cut their attachment holes with the certainty that the rebar would not be compromised and that the plates would fit tightly against the surfaces.
The down time for any electric generating plant is very costly. Any errors in the fabrication of the curved steel plates would have caused considerable delay. And the cost of repairs to the spillway if the rebar had been damaged would have added considerably to the project. The intelligent use of 3d laser scanning to give the fabricators exact measurements of the surfaces and underlying rebar saved a lot of time on the project and substantially reduced the risks.
Do you have questions about how this technology might be applied to your business or area of study? Give us a call or drop a line. (We can also put you in touch with the contractor if desired.)