Peter Kenyon, TunnelTalk

Successful completion of the challenging second and final drive of the Bi-County Water Tunnel in the suburbs of Washington DC spirals the 3m diameter main beam gripper TBM that completed the job into the annals of Robbins history.

Final breakthrough on Bi-County Water Tunnel

The machine that completed the 8.5km water main connector tunnel for the Oscar Renda/Southland/SAK (RSS) Joint Venture was originally manufactured as a 2.7m machine in 1973. On April 26 (2013) it broke through into the Tuckerman reception shaft to wrap up excavation on the US$112.5 million Washington Suburban Sanitary Commission (WSSC) owned project.

"It was a difficult tunnel to excavate," said Jeff Peterson, Resident Engineer for the Construction Management JV of Jacobs Associates and Louis Berger. A TBM breakdown in 2011, followed by difficulties posed by fractured ground, threw the original project delivery schedule out. An excavation program that was estimated at 15 months at project commencement eventually took 32 months. "We are behind schedule but we will be trying to make the time back on the pipe installation side of things," Peterson told TunnelTalk from Chevy Chase, near Washington. "The machine used for the job was refurbished and it is true to say it has had its share of problems. It never really met the advance rates projected, but it got the job done in the end."

"The latest project completion date is currently set at January 2014, but realistically we are probably not going to be done until May 2014. Overall the TBM was fine, and most of the components were new, but these days contractors are having to aggressively bid these jobs to get the contracts. I won't fault them for that, and the owner, WSSC, got a very good price."

When the bids were opened in March 2009 the RSS Joint Venture price of US$112,552,414 came in at nearly US$17.5 million less than the Engineer's Estimate. Other bids were received from Obayashi/Trumbull/Merco JV (US$144,800,000) and Kenny/Shea JV (US$158,247,250).

"Even now, despite the difficulties, there has only been a 1% change on price so the bigger picture here is one of great success because the contractor hasn't had to come back for huge changes," said Petersen. “They overestimated their penetration rates, and this is likely because of the very limited access over a four and a half mile run for this size of machine. Getting maintenance in and material out of a 10ft diameter tunnel with just a single extraction shaft has been a real challenge."

Tim Winn, Principal in Charge for contractor Oscar Renda, said: "We did consider a new TBM, but we knew the history of this machine and its performance in the past. We decided that the rebuild would be better for us economically."

Bi-County Water Tunnel alignment

The 3m diameter machine, featuring its original name 'Miss Colleen', was launched in August 2010 from the main Connecticut Avenue shaft in Rock Creek Park. Work was carried out prior to launch to boost machine power from 600KW to 900KW, in order to accommodate anticipated hard granite rock conditions of 140 MPa. "We also tried to simplify the operator's cab, and increased the bearing size to 2.5m. The rock was very hard, and we were concerned about the length of the tunnel drive with no access. We knew that the larger bearing would provide a higher likelihood of success," said Winn.

One of the challenging features of the Black & Veatch designed Bi-County Water Tunnel alignment, which travels under urban and residential districts at depths ranging between 27m and 84m, has been the limited access. Launch and extraction of the TBM was only possible from the 50m x 10.6m Connecticut Avenue shaft. Following successful completion in early 2011 of the trouble-free 1,257m eastward drive to the Stoneybrook shaft, the machine was backed up the excavated tunnel, as planned, and turned around for the longer 7,240m final drive to the western Tuckerman Shaft.

Problems were encountered barely a month into the longer, second, drive. Just 305m in, the TBM broke down after the pinion gear in the number two gearbox failed. The other three gearboxes and the bull gear were also damaged. Robbins provided full technical assistance to rebuild and improve the damaged machine, and initially performed a refurbishment of the cutterhead and cutterhead bearing support to minimize future potential risk.

Lowering the repaired TBM back into the shaft

After a four month repair delay, the TBM was back in the ground by the end of June 2011, but in early August fractured ground caused another three week delay while steel sets were ordered and installed to support Class III ground. A small section of rock collapsed creating a void about 2.4m deep in the tunnel crown and the TBM suffered minor damage, mostly to the main beam conveyor belt and motor.

Now that TBM excavation is complete, work begins in the next two weeks on installation of 7.25km of 2.13m diameter steel pipeline that will connect the already-installed pipework in the eastern tunnel with the existing mains pipe at the Tuckerman shaft. "The temporary work is done - the final work is more critical," said Petersen.

• Pre-construction and construction phase engineering services were carried out for the RSS JV by Brierley Associates. Pre-construction engineering services included submittal preparation for geotechnical instrumentation, control of water, packaged water treatment facilities, drill+blast excavation, tunneling, rock support, tunnel shafts, and temporary bridge. Brierley also provided engineering services prior to and during shaft and tunnel excavation, including blasting consulting and blast cover design, tunnel utility layout, rail and switch layout support equipment, dewatering design for shaft construction, rock stability analysis, and initial support design for shafts, TBM chamber, and tail tunnels. Full time engineering management for the RSS JV was provided by Brierley Associates during the first year of construction and on an as-needed basis during the second year of construction.

Gallery

Remembering a workhorse machine

According to Robbins, the 2009 pre-project refurbishment carried out in advance of Miss Coleen's latest drives under suburban Washington DC made this the tenth reincarnation of the 40-year-old machine. It has now believed to have completed 48km of underground excavations, mostly for its original owner, US contractor Affholder Inc.

An early factory picture of the Robbins workhorse

The 3m gripper TBM that successfully holed through for completion of the 8.5km Bi-County Water Tunnel is now one of the longest-running machines on the Robbins roster. The TBM was originally owned by Affholder, which used the workhorse machine on nine different projects after purchasing it from new in 1973.

Back in 2000, when 'Miss Coleen' was completing its fourth job at the Plateau Creek Tunnel, Colorado, it achieved a claimed world record in its size class of 67m in a single 10-hour shift.

Project owner, UTE Water Conservancy District, awarded the construction contract for 21km of pipeline replacement to the Barnard/Affholder Joint Venture, with Affholder responsible for the two sections of TBM-bored tunnel. The contractor used the 3.3m Robbins main beam TBM to bore two tunnel lengths of 1,000m and 3,100m through geology comprising sandstone, shale and siltstone with a UCS of 69-172 MPa.

Bob Stier, then of Affholder, was involved in the project. He recalled: "This was an older machine that we had refurbished for harder rock conditions. We increased the machine thrust and increased cutterhead power from 300KW to 600kW. We had new gearboxes, motors, and larger thrust rams added. It was originally the first 2.7m diameter machine Robbins had built, and it was remade to cut very hard rock on the job, up to 175 MPa, very efficiently."

The 4.1km tunnel in Palisade, Colorado, was part of a water transfer project that was completed in March 2001. "Overall maintenance of the machine by the crew helped to keep everything up and running, and advance rates high, for the whole project, not just our record-breaking week," said Stier. Completion of the 1,000m tunnel was completed in approximately four weeks, and after a disassembly and relaunch turnaround period of just 2 weeks, the 3,100m tunnel was completed in six months.

References

WSSC water tunnel pushing progress - TunnelTalk, January 2012
TBM breakdown has Bi-County Tunnel on hold - TunnelTalk, March 2011
Bi-County water tunnel bid result - TunnelTalk, March 2009

Search

TunnelTalk Articles TunnelCast Videos Archive Feedback Current Diary Dates World News Briefs Career Moves Accolades & Tributes Stay Connected Procurement Job Opportunities Equipment Sales DIRECTORY Marketplace About Us Advertising Contact Us Legal Notices Home Office     Latest Alert Alert Signup Alert