Manson is set to complete the Lake Washington Ship Canal Large Lock Center Gate Replacement project in Seattle, WA, in early 2025. The two-year, $18-million project for the United States Army Corps of Engineers (USACE) involved decommissioning the century-old miter gate leaves (the two components that make up the miter gate) and replacing them with two newly fabricated 53-ft by 46-ft leaves and installing connective components.
The Miter Gate Team Prepares for the Job
Starting in the fall of 2022, Manson’s gate replacement project team spent a year procuring materials and planning the upcoming two seasons of work. Key aspects of the project included removal of existing gate leaves, concrete removal, fabrication of new leaves, installation of new concrete and support components, installation of the new leaves, and miter gate commissioning. In addition, the project team and crews performed a preliminary survey to identify critical areas of the leaves and other aging sections of the Locks.
The team worked closely with other Manson departments, leveraging their expertise to develop an efficient method for removing the gate. This included collaborating with Manson’s Equipment Engineering department to refine lifting frame designs for the heavy lift operation using Manson’s DERRICK BARGE 24 (DB24). To ensure optimal performance and reliability, crews conducted comprehensive load tests at Manson’s Seattle yard.
Given the narrow transit through the Locks, the DB24 is an ideal vessel for this project as it is equipped with a detachable sponson—a structure that provides stability for the vessel while floating in its normal operating status. With the sponson removed, the vessel is perfectly sized to maneuver through the Locks.
Performing lifts without the sponson on the DB24 is a project-specific scenario. To stay within the operational safety parameters, the Equipment department worked with a naval architect to perform a stability analysis of the DB24 in this lifting configuration.
The Project Team Arrives at the Ballard Locks
In October 2023, the project team and crew mobilized to the Locks to begin the first season of work.
The project team partnered with USACE to carefully schedule the work to limit interruptions to the Locks. The first step involved working with USACE to activate the local dewatering system, kicking off the first of three dewatering closures. The 30-day work periods began with one to two days to drain the Locks before allowing crews to begin working 24 hours a day for the remainder of each closure. Manson was required to rewater the Locks for 15-day periods between 30-day closures to allow passage for vessels.
Removing the Old Gate and Strengthening Existing Foundations
During the first week of the initial navigational closure, the DB24 crew prepared and lifted each 230-ton miter gate leaf onto the MANSON 73 flat barge.
Transitioning to the concrete removal phase, subcontractor Penhall Company commenced chipping concrete and extracting steel components, including the existing pintle foundation and anchorage area. Using wall saws, wire saws, and core drills, they removed the existing concrete quoin wall and the embedded quoin frame.
Following the removal work, Manson self-performed the installation of a new pintle foundation, quoin wall, and anchorage area. The pintle foundation consists of a concrete footing with a large stainless steel forged base designed to support the gates. The quoin wall is a concrete portion of the lock wall that interfaces with the gates, incorporating embedded stainless steel blocks. These blocks transfer head pressure from the gates to the lock wall during operation.
The anchorage area is the connection point, where the new connection castings and anchorage bars are secured to the embedded anchorage truss and gate.
Crews wrapped up the first season of work in February 2024.
Fabrication of the New Gate
Concurrent with the preparation of the Locks and removal of the old gate leaves, Manson coordinated the new gate leaf design and fabrication of the new gate leaves with USACE Inland Navigation Design Center, and Greenberry Industrial, a metal fabrication company located in Vancouver, WA.
The project team met with Greenberry on a weekly basis to ensure drawings met project specifications. Manson’s project team used a 3-D gate model from the drafting process and survey data to model the gates and the new concrete wall locations to demonstrate proper fit before installation. To ensure pinpoint accuracy during fabrication, the project team kept close tabs during the multistep welding process while creating the new structure. Once the main structure of the gates was complete, the gates were painted with a three-coat paint system which will protect against corrosion. Manson hired a third-party quality control company to ensure the quality of the coating system on the gates. Once the gates were painted, miscellaneous components had to be attached, including castings and rubber seals.
Installing and Commissioning the New Gates
With the fabrication process completed, Greenberry transferred the new gates using a self-propelled modular transporter—a hydraulically operated, multiaxle, remotely controlled vehicle that can move very heavy loads—onto the MANSON 73. The barge was then towed from the Columbia River and up the Washington coastline to Manson’s Seattle yard for preparatory tasks for initial installation. In November 2024, the gates were towed to the Locks for installation.
In early November 2024, the Large Lock was temporarily closed, and tugs brought the DB24 and MANSON 73 into the lock chamber so the crews could install and set the newly fabricated gate leaves.
Given the 10-month lapse between the concrete work and gate installation, a subcontracted dive team cleaned debris from the pintle base and quoin wall prior to installation. Using the DB24, the new leaves were lifted into the upright position and set into place on the previously installed pintle base. Crews attached cameras to the bottom of the gate leaf and used a remotely operated vehicle (ROV) to accurately set the pintle ball on the pintle base. The top of the gate leaf was then attached to the anchorage bars that were connected to the previously installed connection castings. Once set, the gates were moved into the open position and secured until commissioning during the final dewatering period in December.
The remaining tasks will include performing diagonal tensioning, conducting a jacking demonstration using the newly installed top and bottom jacking guides, fitting and adjusting seals and miter/quoin blocks, reinstalling operating machinery on the new gates, calibrating sensors for gate operation, and installing the walkways atop the gates.
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