Achieving earlier arrival of the TBM cutterhead and other components slated for above-grade work required extensive coordination between the contractor and TBM supplier, the latter charged with customizing select components, assembling them for testing, then breaking them back down for shipment to Lorain. Among other modifications, the cutterhead and other outer segments were enlarged to accommodate a 23-ft-dia path, 3 ft wider than originally fabricated for the used TBM's previous work, says Cugini.

The forward shell arrived on site in four pieces, as did grippers. Outer telescoping assemblies arrived in two pieces; the cutterhead and gantry in five. "If components arrived in quarters, we'd assemble them in halves before lowering them to the starter tunnel," says Rehak. Robbins dispatched a chief assembly, hydraulics and electrical technician; a pair of mechanical technicians; and welders to oversee operations and instruct local labor in parts assembly.

For its part, Super Excavators assembled a team of 15 to 20 workers per day per shift, including crane operators, welders and electricians. "We had two or three of our welders working with two or three of theirs," recalls Rehak. "The lead technician would point and tell us what to do and we'd do it."

Super Erectors engaged a Manitowoc 555 and Kobelco crawler crane to assist in operations, the former to engage in lifts of 50,000 to 100,000 lb and the latter to maneuver smaller components from one location to another.

In all, assembly required 12 weeks, from Aug. 12 to Nov. 18, 2013, which was the launch date for mining operations. Of the TBM's myriad parts, only its 232,000-lb cutterhead was completely built above grade before a 550-ton crane supplied by Capital City Group lowered it down the launch shaft in late August.

As a result of final adjustments to both borer and the continuous conveyor system, mining began slowly, advancing only 200 ft during the first few weeks. In one instance, Super Excavators found itself contending with steering snafus, the result of mismatched hoses. Once final adjustments were made, excavation required six months, with soft Cleveland shale facilitating rapid progress—about 72 ft to 80 ft per day.

"That was pretty much our target," says Scot Pearson, ARCADIS senior engineer. "There really were no surprises. Conditions matched those of test borings."

At times, work proceeded at a rate that tested the continuous conveyor's ability to keep up, particularly its vertical segment, says Rehak.

There also were instances when geologic conditions weren't as favorable for lining operations as for mining. Up to 25% of the soft shale geology consisted of layered and laminated rock that broke from tunnel crowns as concrete ring beams were expanded, circumstances that required additional chipping and rock relief.

"That slowed us down a bit, to about 60 feet per day," says Pearson, "but, again, it was expected. In fact, we encountered less than expected."