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Bi-County Water Tunnel
January and February were good months for tunneling. “Miss Colleen,” the name of our tunnel boring machine (TBM), is 11,000 feet in. That’s about 46 percent of the 4.5 mile western leg of the tunnel. The TBM is down for maintenance while the switches for the train tracks are being advanced and a new ventilation shaft to provide proper ventilation for crews and equipment is being drilled near Wisconsin Avenue and the I-270 on ramp.
While you won’t see much activity on the surface for the next few months, Miss Colleen and the piping operation will be very busy as the Bi-County Water Tunnel Project keeps moving ahead.
The site near Tuckerman Lane should be quiet for several months. Work on the shaft is complete and the debris cleaned up. The next step at Tuckerman will be to tie-in to the existing 96” pipe and construct the new valve vault. This work is scheduled to begin during the summer of 2012.
All of the excavation work at Stoneybrook has been backfilled and the surface work, except for restoration, is over. Look at the difference a few months make.
A different kind of work will be beginning soon - all of it underground. The crane will be left in place to lower workers and equipment to begin installing pipe.
The pipe will be delivered to the Connecticut Avenue access shaft and hauled underground to Stoneybrook by the “muck” train that has been converted to handle pipe.
December was a good month for tunneling. “Miss Colleen” is 8400 feet in, about 37 percent of the 4.5 mile western leg of the tunnel.
Crews are finishing up work on the shaft near Tuckerman Lane. The blasting is over, and by the last week in November, all the debris left from the blasting should be cleaned up. The cover will go back on the shaft, the generator removed and the site much quieter for about six months.
Work at the Stoneybrook shaft is progressing and may wrap up shortly after the 1st of the year. The major connections between the existing main, vault and shaft are done. By early next year the Contractor will begin installing the 84-inch diameter pipe from Stoneybrook to the Connecticut Avenue access shaft.
“Miss Colleen,” the tunnel boring machine (TBM), has now tunneled about 7,000 feet to the west toward Tuckerman lane. That’s almost 30-percent of the 4.5 mile western leg of the tunnel.
“Miss Colleen,” the tunnel boring machine (TBM), has tunneled another half mile since our last update. The second and final 4.5 mile leg of the Bi-County Water Tunnel is about 27 percent complete – the tunnel now 6500 feet from its starting point at the Connecticut Avenue access shaft.
Workers will be adding a “switch” to the mini-railroad that runs on the tunnel’s floor so we can operate two trains to carry “muck” back from the TBM as it makes progress. This will allow the TBM to keep working instead of waiting for the current single train to offload and return.
We expect the shaft at the Tuckerman end of the project to be completed by late November. When this shaft is complete, the resources from there will make up a third tunnel excavation and maintenance shift.
The surface structures and piping at the Stoneybrook shaft are expected to be finished in December. When the work is complete, this crew will begin piping from Stoneybrook back toward Connecticut Avenue.
Meanwhile, contractors have drilled pilot holes in three locations for corrosion monitoring and, initially, ventilation. Monitoring equipment will keep track of the condition of the pipe in the tunnel; the shaft also will provide fresh air for crews working on the tunnel excavation.
The Tunnel Boring Machine (TBM) has been making steady progress since August 26th after dealing with a pocket of fractured rock that stopped mining for several weeks. The TBM has grippers that hold onto the sides of the tunnel as hydraulics push the cutter head forward. The fractured rock took away that that hard platform. The TBM couldn’t move.
The area of fractured rock had to be supported with steel and concrete before the TBM could clear the area and resume mining.
Another part of the Bi-County Water Tunnel Project is the drilling of four corrosion monitoring shafts that also provide ventilation while work is going on in the tunnel. Later the shafts will be filled in except to allow for wire leads to run from the pipe in the tunnel up to the monitoring equipment. We’ll have more on that in the coming weeks.
Very few long term construction projects successfully avoid a few hiccups.
Earlier this month the tunnel boring machine (TBM) ran into a pocket of fractured rock. That stopped the tunneling for about two weeks. The picture shows some of the fractured rock the TBM encountered.
Normally, the hydraulic “grippers” of the TBM brace against the hard tunnel walls and push the rotating cutter head against the solid rock ahead. When the TBM hit fractured rock, the grippers couldn’t do their job, and the boring had to stop. The rock also caused some minor damage to the TBM that was quickly repaired. However, tunneling couldn’t continue until steel supports to support the tunnel could be put in place. Those supports, called “steel sets” had to be brought in, so tunneling was delayed for two weeks. Now the TBM can move forward very slowly until it clears the fractured rock area. The walls of the fractured rock have been grouted to provide support for the grippers. This will allow the TBM and trailing gear to completely clear the fractured rock zone.
We hope to be back up to full speed by the end of the month.
While the TBM is following its course about 200 feet below the surface, work on the shaft at the Tuckerman site continues. Eventually, this shaft will be about 138 feet deep with a diameter of 25-feet. Workers are blasting about once a week. This likely will continue for another two or three months.
As you may recall, the new water main will join two existing water mains – increasing capacity and redundancy. Work on the Stoneybrook end of the tunnel will continue for several months. The “tie-in” to the existing bi-county main is complete, and work will start soon on the piping that runs down the shaft and eventually the eight-tenths tenths of a mile back to the Connecticut Avenue shaft. That work will start when a plan is approved for the grouting that will fill in the space between the pipes and the tunnel.
The last parts of our repaired tunnel boring machine (TBM) arrived June 14th, were mounted on the surface and have been lowered into the tunnel. Assembly, testing and startup is underway and “Miss Colleen” may be back in full operation later this month.
She had made her way through 1200 feet of rock before she broke down, but there’s a lot of tunneling to go. The TBM will resume work on the final and much longer leg of the tunnel that runs 4.5 miles from the Connecticut Avenue shaft to the site just off Tuckerman Lane in Potomac.
While the TBM was out of service, work continued on other parts of the project.
Installation of the huge valve at Stoneybrook is complete. It has been tied into the existing water main and will be joined to the new pipeline when the tunnel is complete and the piping installed. The piping operation at Stoneybrook should begin in a few weeks.
We have begun blasting at the Tuckerman site as we continue excavating the shaft. We expect blasting to occur once or twice a week for a period of two to three months.
The repairs to “Miss Colleen” will delay completion of the Bi-County Water Tunnel Project by several months.
The workers at WSSC’s Bi-County Water Tunnel Project have stayed busy while waiting for the return of “Miss Colleen,” the tunnel boring machine that is in the “shop” for repairs.
At the Tuckerman site, excavation is underway and blasting may begin in a few weeks. The blast cover has been fabricated to keep any debris from leaving the shaft. The completed shaft will be 138-feet deep and 25-feet in diameter.
Tuckerman will be the western connection point for the project.
At the eastern end, Stoneybrook, contractors have tied into the piping supplying the old bi-county pipe.
Viewing pictures in the photo gallery, you can see where concrete was cut away from the original pipe so a new “tee” could be welded in place.
The reddish-colored structure is the valve that will isolate the flow of water at the Stoneybrook end. It's about the size of a dump truck and weighs 63,000 pounds. A “riser” pipe coming up from the tunnel and the Stoneybrook shaft will connect to the giant valve. That means there is still of lot work to make the final connection.
“Miss Colleen” should be back from repairs in Solon, Ohio by early June and back in operation later that month.
Engineers won’t know the full extent of the damage until the damaged sections of the TBM have been disassembled at the manufacturer’s for repair. Inspections conducted in the tunnel indicate at least one of the four units that drive the cutter head of the TBM has been severely damaged. There may be damage to the other units and to the “bull gear,” which helps transfer power from the drive units to the cutter head.
The TBM began chewing through 4000 feet of rock on July 23, 2010 from the main access shaft near Connecticut Avenue, and completed the first leg of the tunnel, “holing through on November 23, 2010. Work on the second leg and last leg of the tunnel began February 2, 2011 and was halted February 28th. The TBM had to be backed up to the Connecticut Avenue access shaft for disassembly and removal.
The affected portions of “Miss Colleen” have been shipped for repair to the TBM’s manufacturer, The Robbins Company, in Solon, Ohio, near Cleveland.
While tunneling has been halted, there is still a lot of work to be done at several sites that are part of the project. Workers at Stoneybrook (S-4) are preparing for the eventual installation of a valve, piping and the connection to the existing water main.
At the Tuckerman Lane site (S-1), secant piling is being installed to provide a protective wall for the excavation of the shaft.
The Bi-County Water Tunnel Project will allow WSSC to meet future capacity requirements for Montgomery and Prince George’s counties. The new line will connect an existing water main near I-270 and Tuckerman Lane to an existing water main in Rock Creek Park at Stoneybrook and Beach Drives and have the capacity to carry 100-million gallons of water a day.
The Project has moved into its next phase – boring a 5.3 mile tunnel that will house 84-inch pipe. The Tunnel Boring Machine (TBM) completed the first leg of the tunnel, .8 miles from its starting point at the Connecticut Avenue access shaft to Stoneybrook. “Hole through” took place at 8 a.m. November 23, 2010.
Planning for the $168-million dollar project began in 2004, community outreach in early 2005. Work during the last half of 2009 and first half of 2010 concentrated on constructing two shafts to provide access for and retrieval of a Tunnel Boring Machine (TBM). The main access shaft near Connecticut Avenue just outside the Washington Beltway was finished first. The Stoneybrook shaft was completed second. Work on the Tuckerman site is progressing, with a temporary bridge constructed over a nearby creek and a sewer line re-routed.
Please check back for updates.