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TBM RECORDER       Third breakthrough completes Texas water line 24 Oct 2013
Desiree Willis, Technical Writer, The Robbins Company
Final breakthrough is achieved on the third and last section of the 10.5km Jollyville Transmission Main in Austin, Texas.
Southland crew celebrate breakthrough in Austin

Southland crew celebrate breakthrough in Austin

More than 100m below the ground the 3.25m diameter Robbins main beam gripper machine emerged in the reception shaft to complete its year-long 6km drive. "Mining over 20,000ft (6km) downhill with no intermediate shafts is an impressive feat. A lot of work remains, but it feels good to have this milestone behind us," said John Arciszewski, Project Manager for Southland Contracting.
The distance proved particularly challenging for ventilation and transport at the small diameter: "The distance traveled by the locomotives on this drive alone was over 25,000 miles (40,000 km), all while pulling loaded muck boxes weighing 35,000lbs (16 metric tonne), each up grade," said Arciscewski.
Geology consisted of uniform limestone and dolomite rock requiring little to no support. Although karst features were present throughout the formation, the depth of the tunnel, at up to 107m, enabled the TBM to circumvent them.

3.25m diameter Robbins holes through

Operating at such depth was necessary in order to avoid a sensitive aquifer containing endangered cave-dwelling invertebrates. Six species of spider and insects thrive in and around the karsts and aquifer. Because of this, no probe grouting could be performed due to the risk of seepage into the water features.
The good ground conditions helped the contractor JV achieve a fast advance of up to 210ft (64m) per day on multiple days. "The machine performed well and availability was excellent. Although similar in design to other TBMs of this size, the layout makes it feel like a much bigger machine," said Arciszewski.
The breakthrough was the third and final on the project, following that of a double shield TBM rebuilt by Robbins, as well as a contractor-owned machine.
The completed pipeline will transfer up to 190 million liters (50 million gallons) of water per day from Lake Travis to the Austin Water Utility's Water Treatment Plant 4.
References
High-power TBMs jump start Texas water line - TunnelTalk, September 2012
Tunneling to ease flooding in Austin - TunnelTalk, April 2011
Austin prepares for city center redevelopment - TunnelTalk, January 2010

           

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