Montreal’s rue jarry water Transmission Tunnel is a complex series of tunnels coursing below the city’s streets. Multiple intermediate shafts required a series of launches for the EBC/ McNally JV using a 2.2m diameter Robbins double shield TBM. The contractor prepared for the project’s expected challenges, but even with the best preparation, unexpected events can and did occur.
A NEW WATER MAIN FOR THE CITY
The City of Montreal commissioned the 4.2km tunnel below Jarry Street and 24th Avenue following a sequence of events. Large portions of Montreal are serviced by a single water main, including an area below Pie-IX Boulevard where a pipeline break was experienced in 2002 in a line around 50 years old. Over the subsequent years multiple inspections were made of the repaired line, and it was determined that another pipeline should be built to operate in parallel with the older line.
“The section of the city where we are only has one water main pipe 400mm in diameter,” explains Jean-Sebastien Marcoux, project engineer for joint venture contractor EBC, Inc. “If there is a leak or a problem on this line, a good portion of the city won’t have any water.” With the commissioning of the Rue Jarry Tunnel, the old pipe can be taken offline if further repairs are needed without affecting water supply.
The original bid sent out for the project specified microtunnelling and required at least 10 shafts along the alignment. “When the first plan was determined as over budget, Robbins contacted the city about opening up the bid for a TBM option in addition to microtunnelling,” says Marcoux. “The biggest advantage of the TBM was the length of the drives we were able to do without shafts. We can mine as long as we want with a TBM, but with a microtunnelling machine we would have been limited to 300m at a time.”
EBC/McNally won the second-round bid with a 2.2m TBM that would require just six shafts to be built. McNally took responsibility for the tunnelling work, while EBC began work on surface structures, shaft construction, underground chambers, and worked directly with the city.
Shafts in soil were constructed using wooden retaining walls with welded reinforcements, while shafts in rock were constructed using a hoe ram. The majority of the shafts were rectangular due to the close proximity with city streets. “A circular design would have been wider and the city didn’t want us to close streets to traffic,” explains Marcoux. Five of the six shafts were rectangular, the deepest of these being 17m deep in a 6 x 9m square. One shaft allowed for more space and was built as an 11m deep, 7m diameter circular structure.
“The biggest challenge was excavating deeper without using explosives,” says Marcoux of the structures in hard rock. “Some of them were very close to houses and we had to stay below a strict vibration limit.” EBC upgraded their tools to a larger hoe ram with an extension for the deeper shafts. This made the excavation slower than it would have been with drill and blast, but vibrations were kept below the required limits.
Once the shafts had been excavated, EBC moved on to the starter and tail tunnels, which were allowed to be excavated by drill and blast. “It wasn’t a simple process though,” explains Marcoux. “At shaft 1, we were in the middle of a suburban residential area, 10m from the closest house.” The team utilized carefully controlled micro-blasts to keep vibrations down. The longest of the starter tunnels was 35m long, which would allow for quicker TBM assembly, but in general the starter tunnels were short and required back-up gantries to be operated from the surface until the TBM had bored ahead to give enough space for them to be lowered down.
As the machine was being assembled and the shafts constructed, a launch plan was put into place. Crews would launch the machine at shaft 2, then bore 665m to shaft 3, continuing on another 705m to shaft 6. The machine would then be removed from shaft 6 and relaunched at shaft 1 to bore a 505m-long section. Lastly, the machine would be re-launched at shaft 5 to bore 1,220m to shaft 4 and continue on another 945m to shaft 2.
DIGGING THE TUNNEL
The TBM was initially launched in May 2016. “The machine performed excellent. We had no issues with the TBM at all, just a few things at startup that Robbins helped us with,” explains Tim Cleary, general manager for McNally Construction, Inc. The contractor removed and reinstalled the machine on its first two drives, which were successfully bored in non-abrasive dolomite rock ranging between 150 and 200 MPa UCS.
Then the machine was removed and re-launched to start at Shaft 5. “We installed the machine in December 2016, and had it buried in the 37m-long drill and blast starter tunnel,” says Cleary. The crew bored about 150m ahead in hard rock, installing rock bolts and rolled channels along the tunnel crown at 5ft (1.5 m) intervals. “We were about 160m in when our crew could hear water rushing in from the tunnel face. The next thing they knew there was a river flowing through the tunnel, about 20,000 liters per minute,” says Cleary. The crew were able to safely evacuate, but the same couldn’t be said for the equipment. “The tunnel was filled to the springline within 40 minutes, and the 18 to 21m deep, 6m long x 6m wide shaft was filled within two hours to about 3m below the surface.” The project was halted for about six weeks while the City of Montreal conducted an investigation of the incident. An ROV was employed to take a look at the conditions of the tunnel and the quality of the water, which was crystal clear with no pebbles. Once it was determined that the site was safe, the water was pumped down in stages to monitor if there was any recharge. None occurred and over the course of a week the tunnel was pumped relatively dry.
“We had to gut the TBM, leaving just the shell intact. We rebuilt everything, from all electrics to all hydraulics,” says Cleary. EBC/McNally was able to source parts locally and complete the rebuild quickly. “The day of the flood, my first call was to our electrical engineer. I told him I need to sit down with you tomorrow and go through the electrical drawings. We need to start pricing and sourcing parts locally if possible. Six weeks after that call the tunnel was pumped out and I had an opportunity to go underground to look at the condition of the equipment; afterwards I made a phone call to go ahead and order the parts, and by the time we had pulled the TBM onto the surface, parts were already coming in.”
The team was familiar with taking the machine apart and removing it from the tunnel, and rebuilt it on the surface close to the shaft. “Eleven weeks later we were back up and mining.” For the next 150m McNally opted to use ribs and lagging in lieu of rock bolts and channels. “We didn’t want to hit fractures,” says Cleary. “There were no issues. We averaged 21m per day.” For the remainder of the tunnel drive rock bolts were used and the TBM continued its speedy bore. Three rotating crews worked in two eight-hour shifts, seven days per week, to finish the tunnel—an increase from the previous schedule of two crews working 18-hour days, five days per week.
For EBC, the smoothness of the operation was remarkable: “I think the Robbins machine was the equipment we needed for the job. The TBM was able to get through the conditions; we proved this. We had different rock conditions and different problems, but the job went very well overall,” says Marcoux. Breakthrough occurred on November 14, 2017, within the originally scheduled estimate for project completion. “Our guys worked so hard and we’re so proud of them and how we got back up to speed quickly,” says Cleary.
He also cites good relationships and cooperation between all parties involved as a key part of the success: “The City of Montreal has been excellent to work with. They are very pleased with our performance and how we turned it around so quickly. They’ve said they were really impressed by that.”
With tunneling works completed and hydrostatic pressure tests proving satisfactory, all that remains is some work to backfill shafts and chambers and put the connecting pipe in place. The Rue Jarry pipeline is expected to be operational in June.
