Bi-County Water Tunnel

Project Updates

February 2015

February 2015 updateDespite a few set-backs, we are in the final stretch!

WSSC’s contractor is adjusting the fit-up configuration at the end shaft locations and anticipates complete system tie-in later this month.  Once the tie-in is complete, the line can be placed in service, but additional work on concrete structures and final site restoration will continue through the Spring of 2015.

January 2015

January 2015 updateJanuary was a busy month for this project. A pressure test of the system could not be conducted in December because of an out of tolerance flange.  The flange was re-machined in place and a successful pressure test was completed on January 10.

Backfilling of the 165’ deep shaft S-3 (Connecticut Ave.) was completed and site restoration is underway.


December 2014

The piping in Shaft S-1 was completed on December 10, 2014 and the Tunnel was filled with over 8 million gallons of water in preparation of the pressure test.

November 2014

The final tunnel closure pipes were installed in November 2014.

October 2014

The annular grouting was completed on October 15, 2014.

August 2014

The crew set up for the secondary grouting of the Western leg of the Tunnel (Shaft 1). Secondary grouting is performed to fill any voids that remain in the annular space after primary grouting.

June/July 2014

Throughout June and July, the primary construction activity focused placing grout in the annular space between the exterior of the 84” diameter pipe and the 10’ diameter tunnel. The grouting continued in the Western leg of the tunnel after the ground water challenges were resolved.

May 2014

The Bi-County Water Tunnel media event held May 14, was a great success thanks to over 50 attendees including media, Maryland elected officials, Prince George’s and Montgomery county government agency representatives as well as key WSSC personnel. Individuals had the opportunity to journey more than 160 feet below for a unique view of the upcoming water tunnel, connecting the two counties and providing the infrastructure for continued development.


February/April 2014

As welding of pipe joints continues between shafts S-1 and S-3, the crew has begun to perform contact grouting between shafts S-3 and S-4. However, grouting was stopped in January 2014 because natural ground water flow caused separation in the grouting mixture. As a result, the grouting process was modified and additional controls were added to prevent separation in the grouting mixture.

November 2013/January 2014

The placement of pipe was completed between shafts S-1 and S-3 and welding has continued on those joints. Additionally, annular grout was installed in approximately 3000 linear feet of pipe.

September/October 2013

Work continues in the Western leg of the tunnel. Installation continues for the 84” steel pipe liner as well as the welding of pipe joints.

August 2013

It’s a long slog to install or “fit-up” 4.5 miles of pipe in the western leg of the tunnel.  So far, about 3200 feet of pipe is in place.   Welders have been welding pipe joints since early August and have completed 600 feet of pipe.

Pipe work in the .8 mile eastern leg, including the grouting that goes between the pipe and walls of the tunnel, was performed last summer.

50-foot section of steel pipe delivered to staging area
at Connecticut Avenue access shaft.
Pipe in place in western leg of tunnel


June 2013 Update

Since hole through April 26, 2013, “Miss Colleen” the tunnel boring machine, has been lifted out of the Tuckerman shaft and shipped back to her owner.

Workers have been cleaning the western leg of the tunnel in preparation for pipe installation, miscellaneous work associated with the pipeline tie-in at Tuckerman Lane and grading at the Stoneybrook site at the eastern end of the project.

April 26, 2013 - Video of the Tunnel Boring Machine in action

The mining part of the Bi-County Water Tunnel Project is substantially complete.  The Tunnel Boring Machine “holed through” Friday afternoon at the shaft near Tuckerman Lane and I-270. The 5.3 mile tunnel is now complete and pipe installation on the final western leg of the tunnel will begin in about a month.

Here’s what “hole through” looked and sounded like 125 feet down in the shaft.

March/April 2013 Update

The 5.3 mile tunnel excavation is 98% complete. Approximately 590 feet remains to be excavated along the western end of the alignment near Tuckerman Lane and I-270.

Following completion of the tunnel excavation, the Tunnel Boring Machine will be removed and 24,000 feet of 84-inch diameter steel pipe will be installed and grouted over.

The project is scheduled for completion in 2014.

Shot of the tie-in between the existing 96” main and the valve thatisolates the existing system from the new 84” main.
Wider shot that includes the big hunk of concrete encasing the vault.  The shaft is in the background.

December 2012/January/February 2013 Update

Less than 1700 feet to go before “holing through” at the Tuckerman shaft at the western end of the tunnel.  This is the home stretch for the 4.5 mile second and final leg.  “Hole through” is likely to happen late March/early April. That’s when the mining part of the project will be over.

The tie-in to the valve that sits between the existing 96-inch diameter pipe and the 84-inch diameter pipe of the new tunnel is about 75% complete.

Some of the existing 96-inch pipe was relined with new 84-inch pipe near its connection point with the tunnel.
T-connection:  The upper side of the connection is an existing 96-inch main, followed by a reducer to a 72-inch main.  The pipe to the right connects to the huge valve that sits between the pipe in the tunnel and the existing system.

September/October/November 2012 Update

There is less than a mile to go for the Bi-County Water Tunnel – at least the mining part.

The Tunnel Boring Machine (TBM) has now chewed through 19,200 feet of rock, 4,800 feet short of its target.

When the mining is complete, workers will begin installing and grouting the pipe in this second leg of the tunnel, which runs from the Connecticut access shaft to the Tuckerman shaft. It looks like that part of the operation will be complete in the spring of 2014.

The concrete work for the big valve that will isolate the end of the new tunnel with an existing transmission main has been complete and is ready for the tie-in with the existing 96” main.

After that hookup, WSSC will fill the pipe with about 9-million gallons of water and chlorinate it. The new main could go in service in mid 2014, with additional restoration work on the surface taking a bit longer.

Restoration work earlier this fall at Stoneybook
Concrete work to prepare the valve vault at Tuckerman.

July/August 2012 Update

The Grout Plant.
The Grout Plant

The grouting operation has begun in the tunnel from the Stoneybrook Drive shaft to the Connecticut Ave. shaft, a distance of approximately 3,500 feet. Grout fills in the space between the outside of the 84" diameter steel pipe and the 120" diameter rock tunnel.

We have a grout batch plant on the surface of the Connecticut Avenue access shaft, just outside the Washington Beltway.

The plant has two silos - one for cement and one for fly ash. Grout is formed by mixing three parts cement to one part fly ash, then adding water and chemical additives. Once mixed, it is pumped down the shaft and into the tunnel.

The rate of grout pumped into the tunnel is controlled to minimize the buoyancy forces placed on the pipe. During placement, the interior of the pipe is monitored for distortion and the interior pipe supports are adjusted as necessary to maintain the roundness of the pipe.

Meanwhile, the tunnel boring machine continues to make progress. We’ve mined 22,000 feet or 79% of the total length of the tunnel.

May/June 2012 Update

Piping in the East tunnel is complete. Grouting between the pipe and the tunnel wall will begin toward the end of July.

The mining operation is about two-thirds complete.  We have tunneled 18,900 feet of the 5.3 mile tunnel as of June 12, 2012.

We started installing sheet piling as temporary ground support for the vault excavation at the Tuckerman site. The vault will house the valve and connections that join the existing pipeline to the western end of the new bi-county pipeline.

Excavation may start toward the end of June but most likely will begin after the July 4th holiday.

March/April 2012 Update

Pipe installed in tunnel.
Pipe installed in tunnel.

The tunnel boring machine (TBM) has suffered a few problems and has only been able to mine intermittently.  “Miss Colleen” has made some progress, and is now back on a routine schedule.  She has mined about 12,000 feet along the 4.5 mile western leg of the tunnel.

The .8 mile eastern leg of the tunnel was completed in November 2011, and workers have installed more than 1000 feet of  84-inch diameter pipe and continue to move from the Stoneybrook connection back toward the main access shaft near Connecticut Avenue.

January/February 2012 Update

Lowering Half of Pipe Carrier
Half of the pipe carrier being lowered into shaft.
The two halves are bolted together on the floor of the tunnel.

The first sections of pipe have been delivered to the Connecticut Avenue site. Each section of steel pipe is 50-feet long and lined with ½-inch of mortar.  The first section was “installed” at the Stoneybrook end of the tunnel on 2/29/12. Only 559 sections to go.

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.

Section of pipe rigged to lower shaft.
Section of pipe rigged to lower shaft.
Section of Pipe
Section of pipe.


December 2011 Update

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.

June 2011
January 2012

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.

Rock being poured out of muck car

November 2011 Update

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.

October 2011 Update

Front end loader
A front end loader fills a waiting truck with
crushed rock from the water tunnel project.
 A drill rig near Cedar and Beach works on a corrosion monitoring shaft.

“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.

Muck car
A "muck" car carrying crushed rock from the excavation is dumped.

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.

September 2011 Update

Support system
This picture shows some of the support system that had to be put in place.

We’re making progress on the second and longest leg of the tunnel – from the Connecticut Ave. site just outside the beltway, moving west toward the Tuckerman shaft.  So far we’ve tunneled more than 4,050 feet, about 17-percent of the 4.5 miles we’ve got to mine.

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.

August 2011 Update

Tunnel - Large void in rock above the topshield of the TBM at Station

We’re on the second and longest leg of the tunnel – from the Connecticut Ave. site just outside the beltway, moving west toward the Tuckerman shaft.  So far we’ve tunneled more than 2,600 feet – still a long way to go.

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.

July 2011 Update

Main unit
Main unit lowered

The Tunnel Boring Machine (TBM) returned to work after several months “in the shop.”  Mining resumed in late June and is progressing toward S1, the shaft near Tuckerman Lane and I-270, with still more than 4 miles to go. Repairs to the TBM will delay completion date of the tunnel by several months.

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.

June 2011 Update

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.

As you may recall, the project is connecting two existing water mains, and that involves valves and additional piping at each end so the different water mains can be isolated for maintenance or repair.

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.

Cutterhead and its support 
being lowered into tunnel.
Workmen tightening connections on
the Tunnel Boring Machine.

May 2011 Update

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.


Tunneling in Second Leg Halted - March 2011

Tunneling on the Bi-County Water Tunnel has halted and may be shutdown for several months.  The tunnel boring machine (TBM), known as “Miss Colleen,” sustained major damage during operations.  It was about 1200 feet into the second and final leg of its journey – from the Connecticut Avenue access shaft to a shaft under construction near Tuckerman Lane, a total distance of 4.5 miles.

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.


November 2010 Update

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.

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