Transportation experts know that the cheapest way to move bulk goods is by water. So, the U.S. Army Corps of Engineers (USACE) has been tasked to monitor the system of dams and locks on the Ohio River.
The USACE has focused on a $1.6 billion project to upgrade the Montgomery locks near Pittsburgh. Because of the complexity of the project and the need to keep river traffic flowing during construction, the job will take eight years to finish.
Andrew Byrne/U.S. Army Corps of Engineers Pittsburgh District photo
The Corps of Engineers team is led by Chris Dening, manager of the job, and Jenna Cunningham, resident engineer. Companies rely on the river to deliver unpackaged materials like coal, rock steel, petroleum and chemicals. When the project is completed, the system of locks and dams will enable the amount of commercial river traffic to double on the Ohio River.
"Shipping goods by river reduces the amount of truck and rail traffic," said Dening. "We calculate that it will save some $180 million each year."
"Without a system of locks and dams, the river would alternate between flooding at one time, then be reduced to a trickle at another time," added Dening. "This system of inland navigation helps barges to transit safely upstream and downstream."
The locks were built nearly 100 years ago, so the system is severely overdue for rehabilitation. This river navigation system produces approximately $1.3 billion in economic output and will support approximately 10,000 jobs in the Pittsburgh area over the next six years.
The construction team is focusing on a section of the locks that is among the smallest on the river. The main chamber is 600 ft. long, which is long enough for a nine-barge tow. While the main chamber will remain open during construction, the 360-ft. chamber will be destroyed. The smaller chamber will be rebuilt to 600 ft., essentially doubling the capacity of the locks.
Workers have begun the demolition efforts in earnest, using several excavators with vibratory point attachments to tear into the old concrete. Working around and in water has its challenges. Often operators are working from barges resting in the river and are demolishing to within 2 ft. of the waterline. The demolition activity is expected to take approximately a year.
The enormous chambers are opened to allow barges and recreational vehicles to enter. Once the gates are closed, the chamber is drained to allow ships to exit downriver at a lower water level. Or the chamber is filled with water to raise the water level to enable ships to exit to the proper level for upriver traffic.
Andrew Byrne/U.S. Army Corps of Engineers Pittsburgh District photo
The massive gates that hold water back at either end of the chamber will be replaced and held in reserve in case of a gate failure or will be relocated to other locks on the river. The miter gates on the Montgomery project are 58 ft. wide; one weighs 130 tons the other 175 tons.
These double-leaf gates need to be immense in size and weight to hold back the significant amount of water on the river. The locks perform like a massive river elevator, raising and lowering ships to the proper level so they can continue their journeys.
The chamber that the construction team is focusing on has a land side and a river side. The riverside is where demolition is happening. A middle wall will remain in place so that river traffic can continue during construction.
Once demolition is complete, the crew will begin the complicated process of concrete delivery. The project will require approximately 400,000 cu. yds. over the life of the project.
"We will be producing the concrete at a batch plant we will set up on site," said Cunningham. "The concrete will be delivered through conveyors 70 feet above the river, which is a Coast Guard requirement."
Placing concrete underwater requires special handling. The concrete will have a large-size aggregate (maximum of 3-in. diameter) and will be cooler than normal applications of PCC.
"We plan to do mix testing and several demonstrations before we begin pouring the concrete," said Cunningham. "We will also be drilling steel shafts 30 feet deep in the water, then pour concrete into these trimming pipes. The pipe will be removed when the concrete hardens."
Andrew Byrne/U.S. Army Corps of Engineers Pittsburgh District photo
Construction teams also will build a coffer dam 1,200 ft. long. This water-tight structure will allow workers to "dewater" the area and be able to do near-normal construction activity to support building the new walls of the chamber.
Construction workers will be using a series of tower cranes for their work, including three with a reach of 260 ft. for proper placement of steel and concrete.
Cunningham and her team at the USACE are mindful of the importance of their work for the future of river traffic on the Ohio. At the river's westernmost point, it feeds into the Mississippi River system.
"We will be able to handle these large vessels with more reliability. And we will be able to keep the main chamber open to navigation. Our work is in the best interests of our nation's river traffic." CEG
(All photos courtesy of Andrew Byrne/U.S. Army Corps of Engineers Pittsburgh District.)
