C+S March 2021 Vol. 7 Issue 3 (web)

The York Durham Sewage System Forcemain Twinning Project (YDSS) is a sustainable sewage servicing solution undertaken in the summer of 2019 by the Regional Municipality of York, located north of Toronto, to provide relief for the Town of Newmarket’s original forcemain, as well as resiliency for the area’s overall conveyance sewage system. As the lead design firm on the project, GHD was tasked with all of the pre-design investigation as well as the design, bid, and build process, and coordination of all activities related to approvals and construction. The work involved mining through highly variable ground conditions so concrete forcemain could be laid for a 5.6 km-long sewage pipe running parallel to an existing 36-year-old forcemain through the heart of Newmarket, a city of 85,000. The objective was to provide a dual forcemain system to ensure resiliency in operations and maintenance for the system. A key requirement was to use a construction method that would have the least social and environmental impact due to the area’s highly congested urban setting and natural environment. The solution was microtunnelling construction of a two-pass system consisting of a new forcemain within a micro-tunnel carrier pipe. Part of the initial investigations included a phased geotechnical program to evaluate ground conditions and later identify where ad- ditional geotechnical information was needed to mitigate risk during construction. Part of the process also included establishing value engineering sessions with construction leaders for guidance on the capabilities of the tunneling equipment and procedures to be speci- fied within the design. Project Scope The project’s engineering scope included all preliminary geotechnical, hydrological, and archaeological site investigation and environmental studies, route evaluation and selection, constructability reviews, geo- technical data, and geotechnical baseline reports. GHD was also tasked with hydraulics modelling, geotechnical settlement analysis, noise Light at the end of the tunnel: How technical innovation and community buy-in turned a 5.6 km microtunnelling project into a huge success New sewage forcemain runs below dense urban area including 11 river crossings, three railway crossings, parks, and major city streets By Bradley Marin, Tom Casher, and George Godin

impact assessment and attenuation, detailed design, environmental management, and a comprehensive public engagement program. From a design perspective, GHD was responsible for all approvals, contract document specifications, development of cost estimates, ten- dering and construction contract award, review of shop drawings, con- tract administration, and construction site inspections. GHD was also responsible for administering the commissioning and warranty of ap- proximately 5.6 kms of 1,050-millimetre diameter concrete forcemain to be installed via microtunnelling in a 2,250-mm diameter tunnel. Public Engagement Mitigating the impact of the YDSS Project on the community was a high priority in the planning process. Since the project included cross- ing several regional roads and three live regional transit railway lines, accommodating daily high traffic and rail times was paramount to keep residents getting to work and school on time. A robust stakeholder engagement program involving agencies, landown-



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