The Dalles Dam navigation lock is located within Portland District, U.S. Army Corps of Engineers on the Columbia River between the states of Washington and Oregon in the U.S. The existing downstream miter gate at the lock began cracking near the pintle in the 1970’s after 20 years of service. The gate was repaired in 1980 and performed adequately for another 20 years. Beginning in 2007, a dewatering inspection of the gate identified extensive cracking near the pintle region of both gate leaves. The gate was repeatedly repaired from 2007 to 2009 in an effort to stop crack growth. Each 400 ton gate leaf is 56’ wide by 106’ tall. Due to a lack of miter/quoin block contact, proper load transfer was lost. Consequently the gate experienced considerable cracking in the pintle region, skin plate, lower girders/ribs, and diagonal supports. The bottom rib cracked through the web in September 2009 dropping the gate over ¼” on the pintle requiring a 12 day emergency outage. Additional cracking was identified during the emergency repairs including fatigue driven gudgeon anchor cracking.
Following the emergency repair, the decision was made to replace the gate during a region wide extended lock outage that was planned for December 10th 2010 to March 14th 2011. Design of the new gate began November 10th 2009. The contract was advertised January 15th 2010 and awarded on February 23, 2010. The new gate was installed during the extended outage in March 2010 and has been in service for over 7 years. The new gate was recently subjected to a hands-on climbing inspection in accordance with no signs of distress identified.
The presentation will focus on the causes of cracking, the repair procedures utilized, the cause of emergency gate repairs in 2009 and the lessons learned from these repairs that were utilized in the design of the new gate. Details of the new gate design including adjustable diagonals, self-lubricated pintle bearings, improved fatigue resistant details, adjustable miter and quoin blocks, use of the new Guide Specification 055913, and SMART gate instrumentation will be discussed. The goal of designing the new miter gate was to design a structure in accordance with the latest engineering guidance and to incorporate lessons learned through the experiences with repairing the existing miter gate.