Projects Water

Ohio Canal Interceptor Tunnel

Akron, Ohio

DLZ was selected by the City of Akron to design a tunneled sewer and related appurtenances as a key element of the City’s Long-Term Control Plan to eliminate Combined Sewer Overflows (CSOs) from the Ohio and Erie Canal and the Little Cuyahoga River.

The Preliminary Engineer Report issued in October 2012 recommended designing an OCI Tunnel with a finished inside diameter tunnel of 27-feet and a total length of 6,150 lineal feet, providing a minimum storage volume of 25.6 MG.

After value engineering, the City and DLZ team selected a finished 27-foot diameter tunnel for the final design. The tunnel will be approximately 6,240 lineal feet in length and will convey both dry weather and wet weather flow and provide 26.7 million gallons of storage capacity, which exceeds the USEPA Consent Decree requirements.

The site geology and the urban environment conditions included highly variable bedrock topography, areas of significant fills, and a portion of the tunnel alignment underlying an old landfill. This required careful consideration of several major project features to ensure that the design was constructible, affordable, met the stringent requirements of the USEPA, and acceptable to a variety of stakeholder interests. Close coordination with other consulting teams performing concurrent design development on other elements of the CSO program was also imperative.

The tunnel depth ranged from 160 feet in upstream reaches to nominal cover and “day-light” at the downstream end, which will require ground modification to accommodate TBM operation. The project also includes a downstream tunnel diversion structure with a floatables baffle weir for floatables control and two 48-inch drain lines with plug valves and magnetic flow meters to provide the required flow control. In addition, there are four diversion structures to divert both dry and wet weather flow to the tunnel through the five baffle drop shafts. The two largest baffle drop shafts were physically modeled at the Iowa Institute of Hydraulics Research lab to determine how they would perform since they were beyond the design curves that currently exist for baffle drop shafts. Several computer models were used to evaluate flow conditions, negative impact from surge, and air flow through the tunnel system for potential odor emissions.

An extensive final design geotechnical program consisting of 79 borings, 37 monitoring wells, and 7 test pits was developed to predict ground behavior during construction. In-situ field testing performed included seismic refraction, acoustic televiewer scanning, and Packer testing. The Contract Documents included a GBR to establish contractual responsibilities and define geotechnical parameters.

The tunnel was mined using the single pass system. The type of tunnel boring machine that was used on this project is an Earth Pressure Balance (EPB) TBM, which isl operating in close face mode due to the soil and mix-face conditions at the start of the project, and was switched to an open face mode TBM through the shale bedrock. Precast segmental lining was used to finish the inside of the tunnel.

The project design schedule was very aggressive and included a Consent Decree milestone that had to t be met by the City in order to avoid daily penalties. Throughout the project, the management and design team collaborated in an efficient manner to meet all of the design deadlines in the schedule. The project’s delivery method is not the typical design-bid-build.

DLZ is part of the Construction Management Team (CMT), which includes Parsons-Thomarios-Welty as the Construction Manager and the City of Akron. Work was started at all of the shaft sites and the OCIT-1 Site, the staging site for the tunnel mining. Five of the drop shafts have been excavated and three of them have been completed. Two of the diversion structures have been completed, and the remaining diversion structures are under construction. All three of the Consolidation Sewers have been constructed also. The tunneling work was completed on August 29, 2018.