Approximately 8 hectares (20 acres)
Project Manager representing Infrastructure
Canadian Urban Institute (CUI) Brownie Special Award for Contribution to the Public Realm
The Flood Protection Landform (FPL) project is essential to flood mitigation of the Don River and a key element in Toronto’s preparations for the 2015 Pan Am games. The FPL protects not only the downtown core but also the West Don Lands and adjoining areas, creating approximately 210 hectare (519 acre) of developable land on the previously undevelopable floodplain.
The Flood Protection Landform project is situated on the west side of the Don River, between the rail lands and King Street. The FPL consists of approximately 400,000 cubic metres of specifically engineered fill, extending over an 8 hectare area to a height of approximately 4 metres. The project also includes the construction of a 7m x 8 m x 6.7 m high Backflow Preventer (BFP) structure along an existing 1650 mm diameter storm sewer running adjacent to the King/Queen Street bridge over the Don River. The BFP will prevent the Don River water from flowing into the downtown core through the sewer during a flood event. As part of the FPL project, new foundations are being installed at the three existing bridge columns immediately adjacent to the BFP.
Challenge: The FPL site has particularly complex ground conditions that generated significant technical and schedule challenges for the project. The site is underlain with saturated peat, which would compress with the addition of the FPL weight. Remediation of contaminated soils was also required at the site due to its prior use as a garbage dump. Also, the brittle, 100 year old main sewer line to Ashbridges Bay treatment plans runs under the FPL.
Solution: Removal and replacement of contaminated soil and re-building of the affected sewer line were followed by a period of surcharging, i.e. overfilling the site to squeeze water out of the peat to reduce the potential for future settlements. After sufficient “draining” of the peat was achieved, the surcharge material was removed and replaced with the required engineered material for the FPL.