Fraser River Forcemain Crossing – Land Portion

Client:
District of Mission
Location:
Mission, BC

 
This sewerage system upgrade was performed to increase capacity for conveyance of sanitary flows from the District of Mission to the James WWTP located in Abbotsford. The project involved several stakeholders as works were carried out in two jurisdictions; the District of Mission, and the City of Abbotsford.

Part of the work on the Abbotsford side was carried out in close proximity to existing structures near the James WWTP, namely a methane tank, the James Pump Station, existing clay-lined sanitary storage lagoons, and the nearby CP Rail Main Line. A revised methodology on the Matsqui Slough crossing was necessary to mitigate impact to the above noted structures. Deep trench excavations (up to 6.5m) were necessary for installation of the 900mm diameter steel forcemain within the slough, as well as through the steep banks on either side of the slough. Initial excavations in the area indicated the potential for lateral instability at depth in the in-situ soils. This, along with the close proximity of the nearby structures noted above, warranted the need for an engineered revised methodology.

Installation of the 900mm steel forcemain through the slough was carried out in two phases, the east half, then the west half. An access pad was built within the slough, and moved through each phase in order to allow the slough flows to bypass the site without the need for bypass pumping. An engineer-reviewed temporary clay dam was required on the west half of the slough. All work within the slough was done in consultation with a geotechnical engineer, and included vibration and settlement monitoring.

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