Sewer Tunnel Starts With Assembling a Kit of Parts
The forward shell and sections of the cutterhead were first to arrive. Later came motors, hydraulic cylinders and other parts that were scavenged from other tunneling machines around the world. Some of the components were shipped from as far as Italy, with stops in Baltimore, while others came from Ohio and West Virginia. As the disparate components arrived on site, crews began the task of piecing together a 200-ft-long Robbins double-shield tunnel boring machine they later deployed to mine the 165-ft-deep, 5,500-ft Black River Wastewater Tunnel in Lorain, Ohio. The job marks the first application of onsite, first-time assembly of a TBM in the U.S., according to Michael Cugini, utility tunneling program manager with tunnel machine maker Robbins Co., Solon, Ohio.
"Logistics can pose challenges," says Cugini. "It can be difficult to ship parts where they're needed, when they're needed. There can be issues of oversized or overweight parts that require special transport permits. It can take time. It's not necessarily for every job."
Now that tunnel excavation has concluded and crews have begun disassembling the tunnel boring machine, project engineers say the work most certainly put the contractor and crews through their paces.
"You're not only recruiting labor and cranes to assemble the machine, but bringing in electricians and other trades to weld in electric trays, install transformers and transfer breakers, and erect catwalks and railings," says Gregg Rehak, vice president of tunneling and project supervisor with Menomonee Falls, Wis.-based Super Excavators, Black River's tunneling contractor. "We also were charged with commissioning portions of the assembly as we went along and, when necessary, troubleshooting problems. Some of that required more time than we originally anticipated."
Yet time was the deciding factor as project team members, including the city of Lorain, weighed the merits of remanufacturing the TBM on site or ordering a factory-built, factory-tested unit for the $55.4-million project. Although site assembly carried a slight premium for labor and construction equipment, it shaved three to four months off the schedule, once Lorain accelerated the timetable.
The savings will help ensure the city meets consent-order milestones issued by Ohio's Environmental Protection Agency, which has ordered city officials to eliminate inflow-and-infiltration-induced sanitary sewerage overflows, or SSOs, into the Black River and, from there, Lake Erie during heavy rains.
Timing wasn't always so urgent an issue for Black River, a project that has been off and on the boards for more than a decade. Original plans called for construction of a 12-million-gallon surface equalization storage tank before planned waterfront development nudged the site—and the solution—out of contention. The city and project engineer ARCADIS, Columbus, Ohio, finally opted for a nominal 19-ft-dia deep storage and conveyance tunnel with a capacity of 11 million gallons.
As built, the alignment originates near a wharf and extends alongside the Black River before terminating near the Lorain Black River Wastewater Treatment Plant, the site of a new screening facility, where water diversion will occur. When completed next year, a pump station at the launch shaft will direct water to a sewer interceptor once a water event concludes.
Prior to assembling the TBM, crews dug a 175-ft-deep, 36-ft-dia launch shaft, then a 200-ft-long, concrete-lined starter tunnel at its base to accommodate below-grade assembly of components. As work on the starter tunnel proceeded, the contractor began receiving, sorting and, in some cases, pre-assembling parts, including the drill's cutterhead and shields, on a one-acre plot above grade.
"Operations like this are easier to negotiate above grade," says Rehak. "Whenever we could pre-assemble above grade, we would."