By Tori Durliat
To control stormwater runoff from two new mega malls in Tsawwassen, British Columbia, a large diameter pipeline was designed and installed under the public roads surrounding the sites. The selection of the pipe needed to take into consideration corrosion resistance due to the salt water environment. It also had to offer structural strength because of the poor deltaic soil conditions in this seismically active region.
Built by the Tsawwassen First Nation, the two projects on the peninsula jutting into Boundary Bay are Tsawwassen Mills, an enclosed shopping mall with approximately 111,500 square metres of retail space, and Tsawwassen Commons, a retail outlet with 51,500 square metres of outdoor retail space. The project includes 6,000 parking spaces.
For the stormwater drainage system, SaniTite® HP from Advanced Drainage Systems, Inc. (ADS) was selected. More than 1,500 metres of pipe were used, ranging in diameters from 300 – 1500 mm. In addition, 12 risers were fabricated by ADS using SaniTite HP pipe, all equipped with ladders to provide access to the system.
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Cover over the pipe ranged from 450 mm to 2.3 m and the backfill used was Class 1 crushed 20 mm angular stone. Installed on a zero percent grade, the pipeline acts as a holding tank as well as a conveyance system. This allows water to enter nearby ditches used by local farmers for irrigation.
SaniTite HP pipe in 300 – 1500 mm diameters provides a smooth interior for hydraulic performance and a profile wall (open or closed depending on diameter) for stiffness and beam strength. The high beam strength, in addition to the pipe’s light weight and simple bell-and-spigot joints, allowed contractors to more than double expected production rates, installing more than 60 metres per day in many cases.
The two malls are built on a tidal marsh near the Strait of Georgia, with weak native soils. SaniTite HP provided the required structural strength and joint integrity to perform in this challenging site environment.
Despite the large diameter and integral manholes, the handling and installation of the SaniTite storm sewers on this project was straightforward and troublefree.
Tori Durliat is with Advanced Drainage Systems Inc. Email: info@ads-pipe.com, www.ads-pipecanada.com
Read the full article in ES&E Magazine’s August/September 2020 issue:
