Melvin Price Locks and Dam #26

Lowering the Stress Level

River work is winter work. Under cold, difficult conditions, bridge and lock and dam construction and maintenance take place because water fluctuation usually is minimal and barge traffic slows. So, the U.S. Army Corps of Engineers St. Louis District chose the winter of ’97 to make some updates to the Mississippi River’s Melvin Price Locks and Dam in Alton, Illinois.

Corps engineers needed a stress torsion-monitoring system for the lock and dam’s auxiliary lock, upper and lower miter gates, to determine the stresses that the gates were experiencing and assess their structural integrity. Pointing upstream, miter gates swing open and close on hinges. When the gates are closed, the river current often traps debris at the gates’ entrance, which can exert intense pressure, inhibiting their ability to open.

Silt also builds up, causing the gates’ lower portion to stay static while the top moves, which stresses the gates. Engineers determined that a release of compressed air could blow the silt away from the gates’ threshold and promote its smooth operation.

Wissehr electricians furnished and installed the monitoring system, which includes eight load cells on 3-inch diameter tensioning bolts. They core-drilled 3-inch-thick steel for conduits and cables and installed and connected computer monitoring of load cell outputs to prevent the gate from over-stressing. They also installed power, control and logic for a compressed air, underwater silt-purging system to remove silt before the gates open.

Never Give Up

Wissehr electricians braved the winter wind, working on an aerial platform or from a barge. Conditions proved even more severe than expected when river fluctuations increased. Three times during the project the river level exceeded the limit, and workers had to shut down. They pulled everything out of the lock, flooded it to equalize the pressure and waited for the river level to drop. Then they dewatered the lock again, cleaned out all the muck and started over.

Tom Wissehr, president, says, “It takes a lot of coordination. These are not simple projects because they’re in extreme environments. You have to think harder than the other guy, plan better and work more efficiently.”

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