Dallas gets the tunnel boring machine with a dual-diameter aspect from The Robbins Company.

City of Dallas announces it as "World’s largest hard rock water tunnel boring machine debuts in Dallas".

Their press release reads:

The City of Dallas unveiled the Big Tex tunnel-boring machine (TBM) today at the Mill Creek Drainage Relief Tunnel. The 38-ft by 230 ft long machine is the largest hard rock water tunnel boring in the world at the time tunneling begins. Big Tex will be used to dig a tunnel designed to provide flood protection for east and southeast Dallas. 

“The completion of the TBM assembly marks a major milestone in the Mill Creek Tunnel Project,” said Council Member Lee Kleinman, chair of the Transportation and Infrastructure Committee. “I’m thrilled to see this type of engineering marvel happening right here in Dallas.”

The dual-diameter aspect of the TBM will be a first of its kind conversion process. Big Tex will tunnel the first 9,000 feet of the project, then our team will work completely within the tunnel to remove the outer pieces of the cutter head to convert the overall diameter from 37.7-feet to 32.6-foot diameter. Once the conversion is complete Big Tex will continue tunneling the remaining 17,000 feet of the project alignment.

http://www.dallascitynews.net/worlds-largest-hard-rock-water-tunnel-boring-machine-debuts-dallas