Redeveloping Toronto's Waterfront: Case Study of a Deep Secant Pile Cutoff Wall-Paper

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Toronto’s Port Lands redevelopment is creating a naturalized Don River valley to reduce flooding and provide public green space. Because the reclaimed industrial site contains contaminated fill, construction required a barrier to prevent pollutants entering the river, as well as a dry excavation extending up to 7 m below Lake Ontario and stable excavation walls.<br /><br />For the first construction phase, the project team installed a 1.1-km-long secant pile cutoff wall, reaching depths of up to 45 m. Seepage analyses, informed by extensive bedrock investigations, indicated that the wall should extend at least 3 m into bedrock to limit water inflow and treatment costs. Secant piles were selected for their suitability for hydraulic cutoff and cantilevered earth retention, and their availability enabled a rapid design and construction start.<br /><br />Maintaining wall continuity at depth required unusually tight verticality tolerances. The design specified a maximum deviation of 0.35% per pile, supported by guidewalls, level drilling platforms, and real-time verticality monitoring. Measurements from 817 piles showed that 99% were within the typical 1% tolerance. Calculated as-built overlaps indicated that only one pile pair fell below the 50-mm design minimum; no remedial piles or grouting were needed. Bedrock infiltration testing, streamlined through pilot holes along the wall, helped confirm suitable embedment while reducing construction delays.<br /><br />During excavation, measured water-treatment volumes were generally consistent with design estimates. The excavation was successfully dewatered without overwhelming the treatment system, allowing construction to proceed in dry conditions.<br /><br />The project demonstrates that deep secant pile walls can provide effective hydraulic cutoff, environmental containment, and excavation support when design is grounded in detailed site investigation and construction is supported by rigorous quality assurance. It also highlights the importance of measuring as-built pile positions and verticality when watertightness is critical.

Keywords

Toronto Port Lands

Don River valley

flood mitigation

secant pile wall

hydraulic cutoff

groundwater control

contaminated fill

deep excavation

bedrock embedment

dewatering