The 1997 Regional Wastewater Master Plan identified projects that were required throughout the City to meet the needs of the existing community, as well as future urban growth to the year 2021. R.V. Anderson Associates Limited (RVA) was retained to complete an Environmental Assessment and a functional design for the North Kanata Study Area. The preferred solution, which would meet both long-term hydraulic and condition needs, consisted of a phased approach. The first phase is the replacement of the lower portion of the Tri-Township Collector with 950 m of 1800 mm diameter sanitary sewer.
A key component of the first phase was to construct an 1800 mm concrete pressure pipe, lined for protection from hydrogen sulphide attack and infiltration, under an active railway. The railway authority imposed the condition that the track could not be shut down for more than 72 hours without substantial financial penalties. Due to the depth of the required sewer, (15 m from top of rail to pipe invert) and geological conditions, open cut methods could not be accommodated within the railway authority’s time restrictions.
The preferred construction method was to tunnel under the rail line using hand excavation techniques. The proposed tunnel was 54 m long, and four boreholes were drilled within the tunnel section to determine ground and water conditions. The boreholes showed varying conditions from full soft ground with high water content, mixed face to full rock. The rock was classified as granite. The entry shaft was located on National Capital Commission land adjacent to overhead hydro and telecommunications lines, thus limiting site movements. Due to site conditions a variety of construction techniques were used including hand excavation, rock drilling and hydraulic splitting, and drill and blast. Three types of primary liner were also used, including: 2800 mm diameter steel casing, liner plate, and rib and lagging. The void between the primary liner and pressure pipe was filled using a flowable grout. A settling pond was built adjacent to the shaft site to treat the discharged water to acceptable parameters, allowing disposal into the natural environment.
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