On 25 July, 2022, a crowd gathered as a large Robbins Main Beam TBM, dubbed ‘Big Tex’, broke through in Dallas, Texas, USA. The machine and its continuous conveyor system, for the Mill Creek Drainage Relief Tunnel, successfully bored 8 km (5 miles) in chalk and shale at up to 498 m (1,634 ft) advance in one month.
“I think when you step back and look at what was accomplished by this team as whole, the overall length and size of this tunnel, the TBM conversion, the everyday grind to keep moving forward, it truly is something to be proud of, professionally and personally. No single individual could reach this milestone. It took a great team of skilled individuals. I am fortunate to be a part of it.” said Nick Jencopale, Sr. Project Manager for contractor JV Southland/Mole.
Good advance rates were not the only cause for celebration, the unique project
required a planned in-tunnel diameter change of the TBM from its original 11.6 m
(38 ft) to a more compact 9.9 m (32.5 ft). The first-of-its-kind conversion process was
undertaken 2.8 km (1.7 miles) into the bore and was not done inside a shaft or preexcavated portal. “The TBM conversion was a unique challenge that we were excited
about, and ultimately provided a more efficient method for the desired product
compared to the alternative options. Hopefully the successful conversion proved that
this option can be considered for future tunnel projects.” said Jencopale.
While there were many detailed steps to the conversion process, precision design of
the machine was a key aspect. “We started with a smaller machine, then we made a
kit or second skin that was slightly larger. Then when the time came, we just took that
skin off. It was essentially that simple.” said Evan Brinkerhoff, Robbins Field Service
Manager. The conversion took about four months and was completed in April 2021.