Trenchless Technology

DEC 2018

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W W W.T R E N C H L E S S T EC H N O LO GY.C O M 33 of Montreal are serviced by a single watermain, 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 inspec- tions were made of the repaired line, and it was determined that another pipeline should be built to operate in parallel with the older line. With the commissioning of the Rue Jarry Tun- nel , 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 microtunneling 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 microtunneling ," said Jean-Sébas- tien Marcoux , project engineer for joint venture contractor EBC Inc. "The biggest advantage of the TBM was the we were able to reduce the number of shafts. We can mine as long as we want with a TBM, but with a micro- tunnelling machine we would have been limited to 300 m at a time." The TBM drive required just six shafts and a series of launches for the contractor EBC/ McNally JV us- ing a 2.2-m diameter Robbins Double Shield TBM. Digging the Tunnel The Robbins machine was initially launched in May 2016. The contrac- tor removed and reinstalled the ma- chine on its first two drives, which were successfully bored in non-abra- sive dolomite rock ranging between 150 and 200 MPa UCS. Then the ma- chine was removed and re-launched to start at Shaft 5 in December 2016. " We were about 160 m in when our crew could hear water rushing in from the tunnel face," said Tim Cleary, general manager for McNally Construction Inc. " The next thing they knew there was a river flowing through the tunnel , about 20,000 li- ters per minute," said Cleary. The crew was able to safely evacu- ate, but the same couldn't be said for the equipment . " The tunnel was filled to the springline within 40 minutes, and the 18 to 21 m deep, 6-m long x 6-m wide shaft was filled within two hours to about 3 m 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 tun- nel was pumped relatively dry. " We had to gut the TBM, leaving just the shell intact . We rebuilt everything , from all electrics to all hydraulics," said Cleary. EBC/ McNally was able to source parts locally and complete the rebuild quickly. "Six weeks after that call the tunnel was pumped out and I had an opportunity to go under- ground to look at the condition of the equipment; afterward I made a phone call to go ahead and order parts." The team was familiar with taking the machine apart and removing it from the tunnel , and rebuilt it on the sur- face close to the shaft . " Eleven weeks later we were back up and mining ." For the next 150 m, McNally opted to use ribs and lagging in lieu of rock bolts and channels. " We didn't want to hit fractures," said Cleary. "There were no issues. We averaged 21 m per day." 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 op - eration 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 ," said Marcoux . "Our guys worked so hard and we're so proud of them and how we got back up to speed quickly," said Cleary. Breakthrough occurred on Nov. 14, 2017, within the originally scheduled estimate for project completion. Desiree Willis is public relations manager at The Robbins Company. The EBC/McNally JV celebrate at the completion of Montreal's Rue Jarry Tunnel. The crew overcame a devastating flood to finish the project on time.

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