The Occoquan Dam

VA was retained by Olson Engineering to assist with non-destructive testing (NDT) at the Occoquan Dam in Fairfax County, Virginia.  The purpose of the project was to perform an investigation of the dam’s North abutment (side spillway) using Ground-Penetrating Radar (GPR) to determine the rebar size and spacing in this portion of the dam.

[slideshow]The team accessed the Dam by pontoon boat, reaching the upstream shell of the dam, where we tied off the boat and staged equipment.  Keith and Kevin proceeded to install several temporary anchors into the vertical surfaces of the north abutment so that we could descend safely to the various work areas on the spillway.

We were eating our lunches on the first day of work when the boat began to shake and rattle and bubbles came up from the bottom of the water.  We all looked around trying to figure out who was jumping up and down on the boat.  It took about a minute for us to get the report from Fairfax Water that the shaking had been an earthquake.  Those standing on the dam didn’t feel a thing, continuing cell phone conversations like nothing had happened while the rest of us looked around, confused.

After the earthquake commotion died down, we continued to guide the GPR antenna down the dam on a 2.5′ grid, carefully guiding the equipment on the slippery sloped concrete surface.  The antenna was connected to a data acquisition computer which was controlled at a flat area of the dam by Larry Olson and Aaron Homer from Olson Engineering.