Tough ground conditions had been overcome along the 2km (1.25 mile) drive by the time the 9.26m (30.4ft) diameter Robbins Crossover XRE TBM crossed the finish line to complete for the Akron Ohio Canal interceptor sewer in late August. The TBM was designed specifically to attack the anticipated geology along the alignment that transitioned from soil to partial face shale and into full face shale rock.

“One of the most challenging aspects of this job was that we launched right into the most difficult part of the drive,” said David Chastka, Project Manager for Kenny Construction, a joint venture partner on the project with Obayashi. “We had 60m of soft ground, a very short reach, and then right into a mixed face for 180m. It took a lot of effort to fight through that first 240m.”

XRE TBM faced-down soft, mixed and full-face shale rock

As well as combining features of EPB and hard rock single shield TBM types, the Crossover XRE machine, the first such machine to operate in the USA, was fitted with a cutterhead that could be configured for hard rock or soft ground conditions. The machine operated in closed mode in soft ground and mixed face conditions, and once it hit solid rock crews switched excavation to open mode. A Robbins continuous conveyor muck removal system maintained high availability throughout and supported better than anticipated advance rates. “The machine had the power and made advance rates that we never thought we were going to achieve,” said Chastka. “It was particularly successful in hard rock when advance rates once in full-face shale rock reached a high of 34m (111ft) in one day of two 10-hour operating shifts.”

After achieving breakthrough at the end of August, the machine is being disassembled for removal from its retrieval shaft this Autumn. “The Ohio Canal CSO interceptor is the largest public improvement project in our history and a significant investment in our environment and infrastructure,” said City of Akron Mayor Daniel Horrigan. “Projects of this kind are inherently difficult, and although Robbins is an international company with worldwide repute, we were pleased to work with Robbins as a local Northeast Ohio firm on this significant project.” The TBM was designed and built in the Robbins factory facility in Solon, Ohio.

“I am most proud of the team I had the pleasure of being part of,” said Don Smida, Robbins Field Service Technician. “The amount of daily cooperation and hard work asked of The Robbins Company, the local unions, City staff, and the Kenny-Obayashi JV was important in reaching our common goals.”

The EPA-mandated COS interceptor project includes the 2km conveyance and storage tunnel, as well as drop shafts, diversion structures, consolidation sewers, and related structures, all constructed within in the Akron downtown area.

The first Robbins Crossover TBM to be used in the United States is assembled, factory tested and ready for its work on a short but complex 1.89km (1.17 mile) interceptor sewer tunnel project in Akron, Ohio.

With a diameter of 9.26m (30.4ft) the machine includes features of both EPB and hard rock single shield TBM types to work in both soft ground and open hard rock modes. It will launch from a 12m deep portal site and excavate the first 68m (226ft) in soft ground, transitioning to a 183m (600ft) zone of partial face shale before switching to hard-rock mode for the remainder of the drive in full face shale. Continuous and systematic probe drilling, using two probe drills on the machine, will determine which mode the TBM should be in.

Dressed for hard rock and soft ground excavation

The machine was initially unveiled and factory tested at the Robbins Solon, Ohio headquarters on May 25 2017 before being shipped 40km south to the construction job site. Those present at the unveiling included Akron Mayor Daniel Horrigan, Robbins Chief Engineer Dennis Ofiara, and David Chastka, Project Engineer for the engaged Kenny-Obayashi JV contractor.

Additional aspects of the machine include a versatile cutterhead that is configured with a combination of disc cutters and sacrificial rippers for both the short soft ground section and the longer section in hard rock. The sacrificial rippers will be used in case a cutter becomes blocked. The required rolling torque of the disc cutters has been reduced by 25% to encourage smooth rotation in soft ground. The motors of the Crossover XRE machine have been reworked from an original EPB configuration to permit higher motor speed at reduced torque for the open mode segments of the drive.

Muck extraction from the excavation chamber will be achieved via a durable screw conveyor, the first flight of which is covered with welded-in wear plates. The auger shaft is lined with hard facing in a crosshatch pattern, while the screw conveyor casing has been similarly lined in wear plates and hard facing. A wear monitoring plan has been prepared for the entire drive in order to maximize efficiency in the section of more abrasive rock. Muck will be transported out of the tunnel using a Robbins continuous conveyor system, the 100th such conveyor system supplied by Robbins for operation behind a TBM.

TBM tour during factory acceptance testing

At factory open day (from left) Dennis Ofiara, Robbins Chief Engineer; David Chastka, Kenny-Obayashi Project Engineer; Daniel Horrigan, Mayor of Akron

Many components of the machine were fabricated locally in the northest Ohio area, creating jobs with local sub-suppliers, explained Robbins Project Manager Pablo Salazar. with sub-suppliers, as well as in our own shop.”

The TBM will be shipped in truckloads to the jobsite with the large cutterhead shipped in four pieces. “The entire process of assembly has allowed the contractor to follow closely the testing of the machine, so they are familiar with the TBM at this point,” said Salazar. “At the jobsite and during the drive, we will provide support personnel and supply of spare parts.” Jobsite supervisors from Robbins will help with TBM assembly and excavation for at least the first 1,000m (3,280ft) of boring, which is scheduled to begin in August of this year.

The Ohio Canal interceptor tunnel for the City of Akron will provide control of combined sewer overflows at several regulators in the downtown Akron area. In addition to the 1.89km conveyance and storage tunnel, the mandated project by the US Environmental Protection Agency (EPA) includes drop shafts, diversion structures, consolidation sewers, and related structures. The EPA consent decree specifies that the tunnel must be operational by December 31, 2018.

In Brief

• Robbins Crossover (XRE) TBM 9.26m (30.4ft) in diameter
• First Crossover TBM to be used in the USA
• A 1.89km drive through soft ground, partial face shale, and full face shale rock.