The City of Edmonton's Mill Woods Double Barrel (MWDB) trunk sewer was installed in the early 1970s by open trench and tunneling methods. The MWDB trunk sewer consists of approximately 2,950 m of 1,950 mm and 2,775 mm diameter partitioned pipe which conveys both wastewater and storm water from portions of the Mill Woods area of southeast Edmonton. A number of studies attributed the flooding concerns in the Mill Woods area to the MWDB trunk and recommended constructing a new trunk sewer parallel to the existing MWDB. This paper discusses the challenges and considerations which were addressed by the project team during design and construction of the new storm trunk. The new storm trunk is approximately 3,375 m in length and ranges in size from 2,920 mm to 3,500 mm diameter. The trunk is being installed by tunneling methods at depths varying from 16 m to 36 m. The storm trunk will replace the storm water conveyance function of the existing MWDB. The design challenges and considerations include: hydraulic performance, horizontal and vertical alignment selection, shaft locations, land issues and diversion of existing connections from the MWDB. Construction of this project commenced in the fall of 2010 with the construction of the primary 7.0 m diameter working shaft. Tunneling operations started in early 2011 with the construction of the west leg of the new storm trunk. Two of the main construction challenges include constructing the diversion shafts and reinforcing the tunnel segments for connections.
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