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.Geoenvironmental Engineering III / Session Chair: Catherine Mulligan

Breakout 4
Wednesday, September 16, 2020
10:25 AM - 11:40 AM


Session Chair: Catherine Mulligan


Geosyntec Consultants

Case Study - Challenges faced in Portlands Flood Protection and Enabling Infrastructure (PLFPEI) Toronto project

10:25 AM - 10:40 AM


This paper focuses on the main challenges faced during the installation of a full depth secant pile wall around the perimeter of the area of Work in Portlands Flood Protection and Enabling Infrastructure (PLFPEI) project. The secant pile wall is designed to facilitate excavation and construction of a naturalized river channel to protect against flooding. It consists of 2 components: structural and non-structural. The structural secant pile wall provides support during excavation and backfill operations within the area of Work while both components will serve as a groundwater cutoff wall.
Aside from equipment breakdown and maintenance, several obstacles caused significant delays during construction. For instance, given that the site is adjacent to Lake Ontario, multiple time-consuming measures were implemented to combat the high water infiltration rates. Concrete was placed using the tremie method instead of being free-falled. Sediments were building up at the bottom of the holes in certain locations at rates exceeding 1 m/hour which necessitated clean out procedures either with the drilling or the bailing bucket.
Additionally, the geologic conditions gave rise to certain problems. In fact, the varying bedrock levels lead to piles exceeding 45 m in length in order to reach the required 3-m socket into weathered shale. The deep piles posed a challenge for contractors in regard to the 0.35% verticality tolerance measured by the Jean-Lutz. Boulders and wood obstructions mostly from previous site use caused difficulties in advancing liners at certain sections. Also, since the construction extended during winter, the cold weather caused the winterization of the mobile batch plant and certain equipment including insulating the pump trucks.
The complexity of this project from conception to implementation has advanced the status quo of infrastructure projects in the region through the employment of numerous measures and techniques as highlighted in this paper.