Progress Continues On $250M Columbus LOT Project

Originally published by and shared with permission from Construction Equipment Guide.

Progress on the $250M Columbus LOT project, aimed at reducing sewage overflow into the Olentangy River, is over two-thirds complete with construction on schedule. The project includes a main tunnel, shafts, and complex engineering to address geology challenges. Set for completion by September 2026, the project involves multiple firms and advanced machinery to meet environmental consent orders and improve water quality for Columbus.

Currently more than two-thirds complete, Columbus, Ohio's Lower Olentangy Tunnel project (LOT) is designed to minimize the amount of sewage that overflows into the Olentangy River during flooding. The $250 million undertaking includes a main tunnel of approximately 17,000 ft. of 12-ft. diameter tunnel, at an average depth of 50 ft. This portion is mined with a tunnel boring machine (TBM) and constructed of precast concrete segments.

"Delivering a project of this size requires continuous, close coordination between all parties to effectively complete the work and navigate any issues that may arise," said Jeremy Cawley, project manager of the city of Columbus Division of Sewage and Drainage (DOSD). "We are very fortunate to have, and greatly appreciate, the high level of sharing, cooperation and commitment provided by all the firms involved."

The city of Columbus is under two Ohio Environmental Protection Agency consent orders to improve water quality and reduce the potential for human contact with waterborne pollutants by reducing combined sewer overflows and sanitary sewer overflows into creeks and rivers during wet weather events. Granite Construction serves as the prime contractor on the project, while Black & Veatch is responsible for construction management and inspection services, overseeing and monitoring all aspects of the work.

In addition, Delve Underground is a sub-consultant to DLZ, which is the prime design consultant responsible for the overall design delivery. Delve's duties included assistance with the design of the tunnel and shafts on the project.

According to Cawley, construction is going well.

"Granite completed the mining of the southern portion of the main tunnel from Gowdy Field to Vine Street, which is approximately 5,000 linear feet, and is continuing with the construction of all associated shafts. They are mining the northern reach of the main tunnel and have completed 5,500 linear feet to date. They also are working on the deep rock connector tunnel to the existing OARS tunnel and have finished the mining of the 1,100 linear feet, 90-inch micro-tunnel to the 2nd Avenue site, as well as the jet grouted safe havens along the alignment."

The Gowdy shaft, which is the TBM launch location, was constructed via slurry wall panels and has a figure-eight shape.

"This was done in order to provide flexibility during construction and required dual launches of the TBM," Cawley said. "The contractor completed the southern section of the tunnel first, to potentially allow flow to that portion of the tunnel while they continue construction of the northern section, should issues arise during that piece. This would allow the city to still meet the date requirements of their CSO consent order while the other work is finished."

Work began in 2021, with substantial completion scheduled for the end of September 2026.

"The main challenges for this project are and have been controlling the ground and successfully creating the intervention safe havens via the jet grouting process," said Cawley. "The soft ground geology in Columbus varies widely, and has a large number of cobbles, boulders and gravel which make it very challenging to mine. Because of this, the contractor has to monitor the ground conditions and muck continuously in order to adjust methods and additives to prevent surface settlement and clogging of the machine."

Key tasks remaining for crews include completion of the main tunnel; the deep rock connector tunnel; final build out of all the shafts; as well as the DSR 873 redirection jack and bore. Due to most of the work being subterranean, the weather hasn't had a major impact.

Heavy machinery used on the project includes the new Herrenknecht 14-ft. 7-in. earth pressure balance TBM, specifically designed for the geology of this project and considered the most vital piece of equipment. The TBM was constructed at Herrenknecht's main facility in Shwanau, Germany, and was shipped to Toledo, Ohio, via barge. From there it was transported by Edwards Moving and Rigging in three separate pieces to the Gowdy Field launch site. Setup and lowering of the machine into the shaft was assisted by an 800-ton Maxim crane.

The Herrenknecht AVN 2500 90-in. micro-tunnel boring machine also is being utilized, along with two HS-3180 Liebherr cranes; two Comacchio jet grout rigs; and smaller pieces of equipment.

The main tunnel materials required are the precast segmental tunnel liners being produced by CSI Concrete Systems in Macedonia, Ohio, and the 90-in. micro-tunneling pipe, which was produced by Rinker Materials in Columbus.

Cawley noted the hole through at Vine Street went according to plan. Granite slowed production to more safely excavate through the secant pile shaft walls and came in on line and grade. Work on the 36-in. relief sewer has been completed and was performed with a combination of traditional open-cut excavation and jack and bore methods.

Construction related to the connector tunnel is ongoing. Granite has completed roughly 30 percent of the rock excavation.

"The rock tunnel is approximately 170 feet below the surface, and is being constructed in karstic limestone," Cawley said. "Due to the karst features, Granite is conducting phased grouting of the rock to control the water. The excavation is being completed via drill and blast, sequential excavation methods."

While plenty of work remains, Cawley said he's pleased with what's already been accomplished, due to the talented team assembled to carry out the multi-year project.

"Getting to work alongside and learn from the professionals involved has been an absolute privilege. It's also very rewarding to know this project will provide such a positive and long-lasting impact to the city and region as a whole." CEG

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