For the first time in 35 years, the 255,000-pound sector gates at the Thomas J. (T.J.) O’Brien Lock and Dam are being raised and repaired as part of a critical maintenance project designed to rehabilitate the 54-year-old facility. T.J. O’Brien Lock and Dam is a unit of the Illinois Waterway Navigation System and is located at the entrance to Lake Michigan in Chicago, Illinois.
According to Mike Zerbonia, Illinois Waterway Project Operations Manager, T.J. O’ Brien is unlike many of the other locks and dams in the District. It is unique in that it is designed to maintain navigation but also serves as flood control, for waterway flushing and is part of a diversion control system. With the T.J. O’Brien lock sitting just outside of Lake Michigan, the design of the lock had to differ from those of other locks in the District. On occasion the water level on the downstream side of the dam becomes higher than the lake side and therefore a miter gate or lift gate used by other locks would not be able to function. Instead, a type of gate called a sector gate was used to allow water to move both directions through the T.J. O’Brien Lock.
Sector gates are shaped like a slice of pie with a triangular framework making up the majority of the gate and a solid skin plate that wraps around the outer curved edge. Although the T.J. O’Brien Lock is the only facility in the District that uses sector gates, the design is not unique. Several other locks throughout the country use these types of gates, particularly in coastal areas.
The last time the T.J. O’Brien Lock was dewatered was in 1979 and included the dewatering of the entire lock chamber which took a total of 60 days to complete. This type of extended closure to the Illinois Waterway was not favored by commercial industry that depends on navigation on the Illinois Waterway remaining open even through the winter months. To reduce the impact to the industry, Zerbonia worked with the Maintenance Section, the Illinois River Carriers’ Association and the U.S. Coast Guard to develop a plan for two separate dewatering projects each lasting 47 days with a 30-day open navigation window between the two closures.
“It is important for the Corps to make the necessary repairs to keep the lock at T.J. O’Brien operational,” said Zerbonia. “At the same time we wanted to do our best to work with the industry to lessen the impact made on navigation in a heavily used waterway system.”
The first closure began on Nov. 3 when a set of bulkheads were put into place above and below the downstream sector gates. Once the bulkheads were in place, large submersible pumps were used to remove the water from the gate bay and work could begin on raising the first sector gates using a unique jacking system to raise the 255,000-pound structure. When repairs are needed at the other locks and dams in the District it is common for the Maintenance Section to lift the gates from each lock using a crane and take them to an off-site location for repairs. Due to limited access to the location of the T.J. O’Brien Lock and Dam, this lift process using a crane was not possible due to bridge clearance issues and the overall structure of the gates.
The primary purpose for dewatering the gate bays is to address alignment issues that are preventing proper gate operations. To fix this problem, each gate is being raised which will allow for replacement of the pintle ball, bushings and pins that the gate swings on. The sector gate seals and timbers will also be replaced and the gates will be sandblasted and painted before the project is complete.
“Since it has been 35 years since this lock was last inspected the process of jacking and raising the gates is unlike any project that our current work crew has ever performed,” said Brady Beckman, general foreman for the Illinois Waterway Maintenance Section.
To get a better handle on what the project would entail, Beckman traveled to a lock with a sector gate lift in progress in the New Orleans District, prior to completing the work plan for the T.J. O’Brien project.
“The visit to New Orleans District was very helpful in preparing for the lift here at T.J. O’Brien,” said Beckman.
“There were many parts of the process that could easily be overlooked by someone who had not seen the work performed before.”
The lifting of the sector gates is a complex task and involves a team of about 30 people. At the top of the lock wall there are three pins that must first be removed to release the gate from the wall. Then at seven different locations at the bottom of the gate’s framework, crews use hydraulic jacks to move the gate up a few inches at a time, eventually reaching a height of more than four feet. Lifting the gate is a slow process. Every movement must be monitored to ensure that the gate does not move to one side or the other.
To assist in keeping this project on budget, all of the work associated with the dewatering effort is being performed by District maintenance crews. It has been a collaborative effort with the Illinois Waterway Maintenance Section taking the lead, but many other areas of the District are providing support. Project Management has assisted with scheduling and logistics while Engineering and Construction aided in providing geotechnical monitoring to ensure the process of dewatering the lock would not cause hydrostatic problems. The Mississippi River Project provided additional equipment and staff while the District Safety Offi ce keeps tabs on processes and working conditions.
The downstream set of gates were finished Dec. 21 and the lock was reopened for navigation. It will now remain open until Jan. 21 when the second closure is scheduled. The same process that was performed on the downstream gates will then be done for the upstream set.
Zerbonia said additional maintenance scheduled to take place during the two dewatering periods includes repairs to the bubbler system, inspection of the gate machinery, replacement of the gate track bolts and other minor repairs normally made difficult during regular operations.