In recent years, significant rain events have produced an increase in basement flooding issues in the larger municipalities across Canada. Toronto is one of the municipalities working to address this challenge. To address the flooding problem, the city identified various areas where flooding, particularly, basement flooding, needed to be alleviated.
Study Area 18 is located in the central portion of the city within North York and covers an area of approximately 249 hectares. The area is divided by Bathurst Street and is roughly limited by Highway 401 to the north, Lawrence Avenue to the south, Allen Road to the west, and Avenue Road to the east.
In early 2016, Parsons and Aquafor Beech Ltd. were successful in being awarded the design and contract administration of Area 18 in North York of the Basement Flooding Protection Program. The project required inline storage to protect downstream sewers against surcharging, thus potentially causing basement flooding. The design utilized precast structures to help accelerate the project and ensure that the installation could be completed in the summer of 2019.
In October 2018, the contract for this project was awarded to Trisan Construction. Trisan then turned to their longtime precast supplier, M Con Pipe & Products, to handle the design, production and delivery of these precast box structures.
The design for this project required approximately one kilometer of precast concrete boxes in various sizes from 1800x900mm up to 3000x2400mm to create storm inline storage and reduce the risk of basement flooding in this residential area of North York.
The required precast box culvert sizes and linear meters are as follows:
• 195m of 3000×2000 Box Culvert
• 65m of 2400×1800 Box Culvert
• 115m of 2400×1500 Box Culvert
• 277m of 2400×1200 Box Culvert
• 202m of 1800×900 Box Culvert
• 150m of 3000×2400 Box Culvert
M CON Pipe & Products was given the go ahead in the fall of 2018 to start producing the required structures. This was done in order to take advantage of the capability to produce the required box structures over the winter months and have them ready to ship to the jobsite in early summer 2019. One of the advantages of designing with precast structures is that it allows for the structures to be prefabricated and ready to be shipped before they are required on the job site which helps reduce project delays.
The designers utilized the standards sizes included in the OPSS 1821 specification that provides predesigned box sizes from 1800x900mm up to
3000x2400mm. Since these sizes are standard for precast producers, M CON Pipe & Products was able to have a high rate of production for these structural elements.
M CON Pipe & Products was able to also provide us with a number of precast solutions to help reduce our expected construction schedule. Low flow channels were required inside all of the culvert base slabs. Building these on site, while the culvert was in place, would have been very challenging and time consuming. They were able to cast these channels into the boxes at their manufacturing facility. A number of cast-in-place drop structures were required to allow for storm leads to be connected. M CON Pipe & Products was able to provide precast drop structures attached to the box sections which reduced the construction/installation time.
The depth of these inline storage units varied from 0.6m of cover to 7m of cover. The standard box sizes included in the OPSS 1821 have a maximum depth of 5.5m for 1800mm span and 3.6m for 2400mm and 3000mm span boxes. M CON Pipe & Products was able to adjust the steel reinforcement design to meet this additional loading due to the increased depth of bury.
Some of the box sections required access. Riser sections needed to be added to these specific sections. For these deep access box culvert sections, they produced precast load slabs that would be doweled into the top slab of the box culvert and also have a spigot incorporated into the slab to allow for a maintenance hole riser section to be added. This allowed for quick install of the complete structure.
Given that this project occurred in a residential neighborhood in the summer of 2019, a key part of the success of this project was the ability of M CON Pipe & Products to provide precast solutions which allowed the project to remain on schedule while minimizing disturbances due to construction.
Mark Swan, P.Eng.
Water Practice Lead, GTR
Parsons (Prime consultant for the project)
Will Cowlin, P.Eng., CAN-CISEC
Water Resources Engineer
Aquafor Beech Ltd. (Subconsultant to
Precast Producer: M CON Pipe & Products
Ltd, Ayr, Ontario
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