The U.S. Army Corps of Engineers Walla Walla District successfully repaired a concrete wall on the Lower Monumental Lock and Dam during its annual winter navigation lock outage.
The concrete wall work marks the completion of a three-year phased project to repair cracking and spalling, which occurred along monolith 15 inside the lock. Monolith 15 has a history of cracking and spalling which created unsafe conditions for vessels due to falling concrete. Old concrete from the entire monolith surface—an area approximately 130 feet high by 60 feet wide by 4 feet deep—needed to be replaced to prevent further cracking, spalling and water intrusion to the interior of the monolith.
“The phased construction approach helped minimize impacts to the navigation industry while maximizing repairs within the work-windows and funding constraints,” noted Steve Thompson, Walla Walla District project manager for the wall repair. Each phase of work had unique technical issues, risks, funding, and scheduling challenges. From project planning through construction, the Project Delivery Teams (PDTs) had to be innovative and coordinate with numerous other routine and non-routine project teams at Lower Monumental to ensure products were delivered on time. Coordination of the lock closures with the navigation community and Portland District began several years in advance of the work scheduled, creating the least impact on river commerce.
The concrete wall repairs enhance safety, reliability and structural integrity. The repairs addressed spalling and cracking that’s been occurring since the 1990s and has become more significant in the 2000s plus the impact of an estimated 50,000 navigation lock cycles during more than 43 years of service.
Phase 1, conducted in 2010, removed old concrete from about 100-by-60 feet of the surface. Phase 2, conducted during the 2011 extended lock outage, removed the remaining 30-by-60 feet of surface and replaced it with new concrete up to 40 feet from the bottom of the lock using cast-in-place concrete.
According to Thompson, “Last year’s work was significant for the overall success of the concrete-repair project, which also reduced safety risk.”
The Corps awarded a $969,716 construction contract to Mowat Construction Company of Woodinville, Wash., to conduct Phase 3 repairs which involved anchoring pre-cast concrete blocks into the repair area. Additional work associated with the multi-year project included installing waterstops, grouting cracks and repairing culvert cavitation.
“This is about maintaining safe and reliable passage through the Columbia-Snake river navigation system,” said Thompson. “The completed repair project will improve safety conditions for vessels using the lock and help protect the monolith from potentially damaging water intrusion.”
The project’s importance echoes the Corps’ mission to maintain safe and reliable passage through the Columbia-Snake river navigation system. Each year, the Corps of Engineers’ Walla Walla and Portland districts suspend navigation service at dams on the lower Columbia and lower Snake rivers to conduct annual inspections, repairs and maintenance on the navigation locks at the eight dams between Portland, Ore., and Lewiston, Idaho.
The 2012 lock maintenance outage began on March 6. Navigation locks at Corps dams on the Columbia River reopened their navigation locks on March 20 after completing routine annual inspection and maintenance activities. Dams on the Snake River returned their locks to service on March 27.
The Columbia-Snake river navigation system is vital to the economic health of the Pacific Northwest. The system accommodated the transportation of an average of 10 million short tons of cargo annually from 1999 to 2008, according to the Corps’ Waterborne Commerce Statistics Center. Ten million tons equals about 2,700 barges, 100,000 railcars or 350,000 semi-trucks.