Distinguished Webinar Series

Organized by Canadian Association for Earthquake Engineering and Seismology /
L’Association Canadienne du Génie Parasismique et de la Sismologie

John Hart Dam Seismic Upgrade: A Robust Seepage Barrier for Cascadia Megathrust Resilience

Date: Wednesday, October 8, 2025, Time: 3:00 p.m. ET, 12:00 p.m. PT

Abstract

The John Hart Dam, constructed in the late 1940s on Vancouver Island, required upgrades to address seismic vulnerabilities and ensure resilience against a potential magnitude M9 mega earthquake originating from the nearby Cascadia Subduction Zone. The Middle Earthfill Dam (MED), one of three earthfill structures at the site, was determined to be at risk of flow slide failure or significant displacements due to liquefiable and strain-softening foundation soils. Many conventional ground improvement techniques were unsuitable due to environmental sensitivities, constructability challenges, and dam safety concerns, especially given the need to avoid reservoir drawdown and cofferdam installation. To overcome these limitations, a range of solutions—from straightforward to moderately complex—were implemented to rehabilitate the various structures. These included an upstream buttress berm with dredging and replacement under full reservoir conditions, unloading by excavation, and a downstream toe berm reinforced with steel pinning piles. A key element was the construction of a new Plastic Concrete Cutoff Wall (PCCW) to replace the vulnerable slurry trench cutoff wall, providing a robust and seismically resilient seepage barrier. The PCCW was embedded into bedrock or silt and constructed with a suitable mix to ensure durability and reliability. The presentation will outline the overall upgrade strategy and focus on the PCCW’s design and construction, highlighting key challenges and performance verification. The seismic upgrade of the dam is ongoing, with the PCCW completed in early 2024. (https://majorprojects.ca)

Presenter

Thava Thavaraj, Ph.D., P.Eng. Senior Geotechnical Engineer/Principal Klohn Crippen Berger [email protected] CAEES-ACGPS Secretary

Thava serves as a Senior Geotechnical Engineer/Principal at Klohn Crippen Berger, bringing more than 25 years of experience in seismic design, seismic hazard assessment, and geotechnical engineering. He earned his PhD in Civil Engineering from the University of British Columbia. His career has centered on leading site-specific seismic hazard assessments, seismic design, seismic safety evaluations, and seismic upgrades of existing infrastructure, including hydroelectric dams, tailings dams, bridges, and port structures on projects in Canada, the USA, and internationally. His specialization lies in advanced numerical modeling, particularly in seismic deformation and soil-structure interaction analyses. Thava has had the privilege of working with some of the world’s leading experts in seismology and earthquake geotechnical engineering, developing at times innovative or unique solutions to challenging problems. He has led or contributed to the seismic upgrades of hydro dams, bridges, and port structures in BC, significantly enhancing their seismic resilience. Thava has authored more than 45 papers, mostly on the seismic aspects of dams and bridges. He is the lead designer and engineer of record for the seismic upgrade of earthfill structures at the John Hart Dam.

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