TBM breakdown has Bi-County Tunnel on hold
Mar 2011
Paula Wallis, TunnelTalk
- Excavation is at a standstill on the Bi-County Water Tunnel in Washington DC after the TBM went down on February 28, 2011.
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TBM ready for launch in June 2010 (Photo by - WSSC)
- "The TBM lost one of the gear boxes on the number two motor," said Steve Pinault, Project Manager for the Owner, Washington Suburban Sanitation Commission (WSSC). "There are four 300hp motors with associated gear boxes and pinion gear that tie into the main bull gear, and a pinion gear in the number two gearbox failed."
- The 10.6ft (3.2m) diameter machine, a used Robbins main beam gripper TBM, completed its first 4,124ft (1,257m) drive from the launch shaft at Connecticut Avenue, east to the Stoneybrook Shaft in November 2010. The machine was removed and re-launched in early February (2011) for its second, and much longer 4.5-mile (7.2km) drive west to Tuckerman Shaft when it broke down (Fig.1).
- "Work was only about 1,000ft (305m) into the drive, said Pinault, "and the machine was able to back up under its own power. The gripper system was used to back it up in four foot strokes, which took a couple of weeks to accomplish."
- Once lifted to the surface, the bearing and drive units were removed and shipped back to the Robbins plant in Ohio where representatives from the contractor, Renda/Southland/SAK JV, arrived yesterday (Thursday, March 24) to assess the damage.
- "We do know that one gearbox has to be replaced, and that the bull gear and the other three gearboxes are damaged," said Pinault, "but we don't know the condition of the bearing and we're not quite sure what it will take to repair the bull gear. If the bearing is bad, there is a spare and it will have to be fitted. If the bull gear needs replacing, one has been located, but we don't know how long it will take to get it. The bigger concern is the gearboxes. There is one spare drive and pinion, but not four. If the other three are damaged beyond repair, and the parts are difficult to get, that will determine the total length of the shutdown."
- The Owner said Robbins has been responsive and cooperative. "We were called in to inspect the damage and we are now reviewing the items that have just arrived into our workshop," said Brianna Home, Robbins' spokesperson. The parts will be completely inspected and at that point we will be able to advise on the extent of the repair works and when the machine can be back to operation."
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Bi-County Tunnel alignment
- Home stressed that while the machine was originally rebuilt and upgraded primarily by the contractor and other suppliers, Robbins has offered to fully assess the situation. "Robbins will provide full technical assistance to rebuild the damaged machine and put it into a condition to minimize future potential risk." The refurbished TBM is one of Robbins' longest running machines. Before this job, it had completed nine tunnels for a total of more than 21 miles (35km) since it was put into service in 1973. The machine is now owned by SAK.
- Pinault said the cause of the failure is still unknown, but that it appears to be a mechanical or material failure, not caused by any geological feature. "We are not aware of any adverse ground conditions, and the contractor is not claiming any," he said. "We don't know if the bull gear went first and damaged the gearbox and the pinion, or if the pinion went first and damaged the bull gear. Until we know the cause, we won't know what the fix is."
- Pinault said, optimistically the earliest the TBM could be back in service is mid-May, but that, depending on the damage and the availability of parts, excavation could be delayed for months. The contractor has plenty to do in the meantime he added. Excavation began last month on the Tuckerman Shaft, the last of the three on the project; at the Stoneybrook Shaft a control valve vault has been completed; and WSSA is in the process of shutting down the old Bi-County tunnel to allow the contractor to complete the steel pipe tie-in over the next two to four weeks. Following the tie-in, installation of about 4,000ft (1,219m) of steel carrier pipe will begin in the completed drive and working toward the Connecticut Shaft.
- Work began on the $112.5 million deep hard rock tunnel in the Fall of 2009. The 180ft (55m) launch shaft was complete and the TBM lowered in June 2010. Pinault said the first drive was uneventful. Ground conditions were as expected, water inflows were less than anticipated at about 100gal/min and that there have been no claims above and beyond what was expected in the GBR.
- The tunnel is designed to meet future water demands in the suburban Washington DC area and was scheduled to be online by 2013. That timeline may be revised depending on the extent of the TBM repairs.
- Bi-County water tunnel bid result - TunnelTalk, March 2009
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