Traffic was slower than usual across the Garrison Dam today.
The reason for the slow-down was the need to inspect some recently-discovered damage to one of the bridge supports.
Jim Olson reports on what was happening today to look inside the concrete pier that was showing some cracks.
This crack caught the attention of inspectors at the Garrison Dam
(Todd Lindquist, Garrison Dam Operations Project Manager) "We decided we needed to bring in a bridge expert and do some ground-penetrating radar testing to see what was going on inside the pier."
The crack is in one of the dozens of concrete piers that support the highway that crossed the dam. And so traffic was altered a bit as engineers took to the top - and underside of the highway, using specialized, ground-penetrating radar to inspect the damaged pier.
(Todd Lindquist, Garrison Dam Operations Project Manager) "He's doing the ground-penetrating radar testing right now..."
The work started under the roadway - with bridge specialists marking and peering into the concrete. It's a procedure Todd Lindquist of the Corps of Engineers says anglers can relate to.
(Todd Lindquist, Garrison Dam Operations Project Manager) "Very similar to a fish finder or depth finder on the reservoir where it will penetrate the concrete structure, tell us where the crack is located - similar to the bottom of the lake, and then it will also reflect back off the rebar so we will know the depth and locations of the rebar."
After the underside passes were complete, they inspection moved topside
(Todd Lindquist, Garrison Dam Operations Project Manager) "The radar will penetrate about 22 inches deep so they're looking at it from all sides."
The crack is directly across the roadbed from another crack that was discovered about five years ago. Engineers placed a steel plate on that pier and filled in the crack. Lindquist says the theory about why this spot has developed two cracked piers revolves around the design that calls for the heavy bridge deck to rock back and forth on these plates.
(Todd Lindquist, Garrison Dam Operations Project Manager) "Over the years we figure that corrosion and rusting are not allowing that bearing plate to slide so it's pulling on the top of this bearing plate and pulling the top of the concrete."
He says repairs on the new crack will certainly be done - but the radar inspection will help determine how much must be done.
(Todd Lindquist, Garrison Dam Operations Project Manager) "We know we're going to make some repairs. The reason we're doing the further investigation is to determine if it warrants any load restrictions across the bridge. The bridge is about 60 years old and we do have some movement and we're not overly surprised to see this after so many years."
And the engineers in charge of the dam will be paying close attention to make sure the structure serves its purpose for several more decades. At Garrison Dam, Jim Olson, KX News.
Lindquist says temporary supports will be used to shore up the cracked pier, allowing normal traffic flow while engineers decide on the best permanent fix for the concrete support.