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Keynote Speakers

R.M. Hardy Keynote Address

Risk-informed Decision-Making: necessary insight to reduce risk

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Suzanne Lacasse

Abstract

The 2024 Hardy lecture focuses on the benefits of adopting a risk-informed approach and proposes a risk-informed decision-making (RIDM) framework. Four steps characterise the framework: 1) assemble all available information and conduct deterministic analyses; 2) conduct a risk assessment, identify the most significant factors influencing the safety, and prepare a risk picture using risk diagrams; 3) make risk-informed decisions to reduce risk; and 4) do regular reassessments of the risk as it can change with time. Basic concepts of a risk-informed approach are illustrated with examples from practice for slopes in sensitive material and for both embankment and concrete buttress dams. Many probabilistic tools can be used for risk assessment, from simple qualitative estimates to full probabilistic multi-parameter modelling of the hazards and consequences. The effect of risk mitigation measures for landslide and rehabilitation measures for dams is also considered in the examples provided. For landslides, the web-based database and portal LaRiMiT (Landslide Risk Mitigation Toolbox) for identifying and optimising the selection of mitigation measure is demonstrated. An important benefit of the RIDM is the added insight gained by integrating risk assessment in the stability evaluation of slopes and dams. The advantages and drawbacks of the risk-informed approach are discussed.       A risk diagram is also shown to be an effective tool to communicate with stakeholders. In addition, risk analyses, once established, can be adjusted and revised at regular intervals at relatively low cost. The lecture concludes with learnings from the case studies and a recommendation for wider implementation of the risk-informed approach in practice.

Biography

Dr. Suzanne Lacasse obtained a Bachelor of Arts at the University of Montréal and civil engineering degrees from Polytechnique Montréal and the Massachusetts Institute of Technology (MIT). After 12 years on MIT's faculty, she moved to the Norwegian Geotechnical Institute (NGI), where she became Managing Director NGI from 1991 to 2011. She has given the Terzaghi Lecture, the Rankine Lecture, the Jennings Lecture, and the Terzaghi Oration. She has received many awards, including the Canadian Geotechnical Society Legget Medal and the Kennedy Medal of the Engineering Institute of Canada. Dr. Lacasse received PhD's Honoris Causa from the University of Dundee, the Norwegian University of Science and Technology, the University du Québec and Queen’s University. She is an elected member of the National Academy of Engineering in the USA, Canada, Norway and France. She is a member of the Royal Society of Canada, the Royal Academy of Norway and the Norwegian Academy of Science and Letters. Dr. Lacasse is Honorary Professor at Tongji and Jiaotong Universities (Shanghai) and Zhejiang University (Hangzhou). She   is an Officer of the Order of Canada and a Knight of the Order of the Falcon in Iceland.

Hydro-Québec experience with the design and construction of large rockfill dams

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Pierre Vannobel

Biography

Pierre Vannobel is a graduate of the Université de Sherbrooke in mechanical and civil engineering. He also holds a master's degree in geotechnics. He has 35 years of experience in the dam industry. From 1988 to 1991, Mr. Vannobel held several positions with companies that were eventually integrated into SNC-Lavalin, and then worked for the latter until 2001 when Mr. Vannobel joined Hydro-Québec. He is one of the few practitioners with expertise in both dam design and construction. Mr. Vannobel has been actively involved in the design and construction of more than 300 hydraulic embankment structures. His contribution to numerous hydroelectric development projects has earned him renown in the Quebec dam industry.

Abstract

The presentation provides a comprehensive summary of the experience acquired during the design and construction of several large rockfill dams at Hydro-Québec. These activities have taken place as part of the development of new hydroelectric installations by Hydro-Québec since the 1970s. More specifically, four types of rockfill dams are discussed: 1) with a very deep plastic cut-off, 2) with a thin central bituminous concrete core, 3) with a wide central core in glacial till, and 4) with a wide inclined till core.

The particularities of the concept characterizing the various typical cross-sections of said rockfill dams are presented and discussed, with emphasis on the materials constituting the zones of these structures. Particular attention is paid to the materials used for impervious elements, filters, transitions, large-scale rockfill and slope protection rockfill, including upstream riprap.

In order to respect the particularities of each type of dam, or even certain specific environmental constraints (e.g., with treatment aimed at removing fine particles), the presentation focuses on: 1) the development of state-of-the-art knowledge, 2) the study of the placement and performance of the plastic materials of the cores (plastic concrete, bentonite-enhanced till and bituminous concrete), and 3) the study of large-scale rockfill (maximum diameter, thickness of lifts, number of compactor passes, compaction energy, in-place moduli of elasticity, Vs1)

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