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Contractors go deep on sewer construction project

Tunnel boring the key to successful installation as part of major Ontario road project

Contractors go deep on sewer construction project

Designing and overseeing a major sewer installation project is never easy. When construction needs to be nearly 30 metres underground and pushed through shale rock, it’s even more of a challenge. When the Region of Peel needed to widen sections of Mississauga Road and install a trunk sanitary sewer to service the growth of northwestern Brampton, the depth was a large potential roadblock. To help address that challenge, the Region hosted a competitive request for-proposal selection process to retain a consultant to design, coordinate, and monitor the complex project during construction. Based in Vaughan, Ontario, The Municipal Infrastructure Group (TMIG) was founded in 2003 and serves the Greater Toronto Area. Partners David Scott, David Ashfield and Mark Tarras head up a team of 60 engineers and technicians who handle everything from studies to major infrastructure. TMIG also provide services during construction on both private and public infrastructure projects with a focus on water, wastewater and stormwater.

In the case of the Mississauga Road Improvement Project (MRIP), TMIG was the primary consultant on a project that began in 2008 and concluded this year (minor road works are still in progress; however, the 1,200mm diameter trunk sanitary sewer is complete and operational). The project included a wide range of sewer installations and related improvements, much of which was conducted underground. The project included shafts design, tunnel design in rock, and pipe installation and grouting, including dewatering and co-ordination with public agencies. The amount of infrastructure installed using trenchless methods increases on a daily basis. It can result in significant savings, especially in urbanized and congested areas that contain large amounts of existing infrastructure. “Trenchless work is becoming a larger portion of underground work thanks to ever greater development,” said Arbinder Hundal, senior project manager with TMIG. “Before, we may have done major road crossings using open cut methods, but it’s become very difficult to do that because of what is already underground,” Hundal said. “Cost benefit analysis compares the installation using various means. More often than not, trenchless methods show that the planned infrastructure can be installed more cheaply with fewer environmental challenges than open cut. Municipalities are now much more proactive in addressing and meeting the concerns and needs of their community. These concerns also form part of the analysis in deciding the methods to be used for the installation of planned infrastructure.”

The shafts dug to launch and recover the Lovat TBM used by McNally had to be dug out to an average of 20 to 28 metres. The contractor bored a 2,400 mm tunnel for the 3.2 km length of the project, and the 1,200 mm concrete pipe was installed afterwards.

For Mississauga Road, the sewer project was part of an ongoing road project. About 2 km of 1,200mm concrete pipe was required to run through shale rock, Hundal explained. To do so, McNally Corp. was subcontracted by primary contractor Fermar Paving for tunnel construction. “The tunnel was required to convey sanitary flow from proposed residential areas in order to accommodate the growth of northwestern Brampton,” Hundal said. “We had to go under proposed roads and infrastructure, which pushed the tunnel even deeper.” In fact, the shafts installed to launch and recover the Lovat TBM used by McNally had to be dug to an average of 20 to 28 metres. The contractor bored a 2,400mm tunnel for the 2km length of the project, and the 1,200mm concrete pipe was installed afterwards. A series of 3m manholes were also constructed along the way. The construction went relatively smoothly, Hundal noted, with only minor issues arising during the project. An excess of water in the shaft required some additional pumping and permitting but was managed relatively easily. Of greater concern was a problem that arose when the TBM was nearing the end of the bore.

“The TBM is very accurate. It used to be that these machines would use lasers to control their path, but now they use gyroscopic controls, with various backups,” Hundal said. “About six metres before the end of the tunnel, the gyroscope broke down - but they finished it blind and within millimetres of the intended target.” With the tunnels complete, attention turned to the pipe itself. Concerns about hydrogen sulphide gas causing corrosion in the difficult-to-reach pipe resulted in the selection of a special treatment, Xypex, to help protect the concrete. “This treatment has been used in the U.S. in very corrosive situations,” Hundal said. “It’s mixed in with the concrete and becomes part of the pipe itself. It makes the concrete a lot more impervious while increasing its resistivity to corrosive environments.” Overall the sewer project took two years to complete, along with some additional connections, and it is now in operation. “If you go to Mississauga Road now, the shafts have been backfilled and you would never know that anything had taken place,” Hundal said. “There’s no real evidence but the manhole covers.”

For Mississauga Road, the sewer project was part of an ongoing road project. About 2 km of 1,200mm concrete pipe was required to run through shale rock, Hundal explained. To do so, McNally Corp. was subcontracted by primary contractor Fermar Paving for tunnel construction. “The tunnel was required to convey sanitary flow from proposed residential areas in order to accommodate the growth of northwestern Brampton,” Hundal said. “We had to go under proposed roads and infrastructure, which pushed the tunnel even deeper.” In fact, the shafts installed to launch and recover the Lovat TBM used by McNally had to be dug to an average of 20 to 28 metres. The contractor bored a 2,400mm tunnel for the 2km length of the project, and the 1,200mm concrete pipe was installed afterwards. A series of 3m manholes were also constructed along the way. The construction went relatively smoothly, Hundal noted, with only minor issues arising during the project. An excess of water in the shaft required some additional pumping and permitting but was managed relatively easily. Of greater concern was a problem that arose when the TBM was nearing the end of the bore.

“The TBM is very accurate. It used to be that these machines would use lasers to control their path, but now they use gyroscopic controls, with various backups,” Hundal said. “About six metres before the end of the tunnel, the gyroscope broke down - but they finished it blind and within millimetres of the intended target.” With the tunnels complete, attention turned to the pipe itself. Concerns about hydrogen sulphide gas causing corrosion in the difficult-to-reach pipe resulted in the selection of a special treatment, Xypex, to help protect the concrete. “This treatment has been used in the U.S. in very corrosive situations,” Hundal said. “It’s mixed in with the concrete and becomes part of the pipe itself. It makes the concrete a lot more impervious while increasing its resistivity to corrosive environments.” Overall the sewer project took two years to complete, along with some additional connections, and it is now in operation. “If you go to Mississauga Road now, the shafts have been backfilled and you would never know that anything had taken place,” Hundal said. “There’s no real evidence but the manhole covers.”