Constructing the forcemain within the tunnel also required a unique approach. This meant using pre-stressed cylinder pipe segments within the precast tunnel sections to address the internal pressures from the forcemain as well as the external soil loads. Pipe segments had to be carefully placed within the tunnel to account for both horizontal and vertical curves and all connection points. Pipe segments would need to be interconnected, blocked in place, tested and then the annular space filled with grout to ensure system reliability. It Takes a Village The planning efforts of York Region leading up to the project were critical in laying an important foundation for success. Up-front com- munity consultation, engineering studies, and quality assurance efforts all contributed to the successful completion of the project—ahead of schedule, within budget, and mindful of the needs of the community. York Region listened to community concerns and responded with prac- tical solutions to address traffic concerns, noise, vibration and light issues, tree and wetland protection, as well as minimizing disturbance to existing utilities. The project minimized the number of tunnel shafts to ensure community services would not be adversely affected. The natural environments of the Town and the East Holland River Flood plain were protected by reducing shaft compound size, selecting locations outside the flood plain and maximize the spacing between shafts. With microtunnelling being used as the construction method, long distances of forcemain could be installed between shafts. This meant trees and vegetation were not disturbed and parkland remained in use throughout construction.
above. The face of the tunnelling equipment was armed with rear load- ing cutting disks and tools that would accommodate for the excava- tion of the highly varied soils with the potential for cutting through large cobbles and boulders. The tunnelling equipment was specified with face access as a mitigation measure to accommodate changing out of disk cutter should it become necessary. Hyperbaric intervention was also used to give workers safe access to the face of the tunnelling equipment under pressure. Technical Excellence and Innovation It was critically important for the project to have as little impact as pos- sible on the surrounding area’s urban setting, and to ensure protection of the East Holland River floodplain and natural environment setting, which cuts through the heart of Newmarket. As a result, the 5.6 km pipeline was constructed with a limited number of shafts and with the rare use of back-to-back microtunnel drive lengths in excess of 500 meters. Extensive geotechnical analysis, along with value engineer- ing consultation and risk mitigation actions, provided the Region with added confidence for the project to proceed as designed. The placement of shafts was key to productive mining, so shaft sites were selected using a carefully established decision matrix. These sites allowed for the delivery of material along a controlled haul route to minimize community traffic and noise impact. All equipment and material entered the shaft and was installed within the shafts and the newly constructed tunnelled sections. Even though microtunnelling took place 24 hours a day, traffic to the shaft locations was restricted to regular construction hours. This required all excavated material and new precast tunnel segments to be supplied strictly within a 12- hour window.
BRADLEY MARIN is GHD North America Tunnel Service Lead. GEORGE GODIN is GHD Water Market Principal. TOM CASHER is GHD Water Market Principal.
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csengineermag.com
march 2021
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