Geotechnical Risk, Regulation, and Public Policy (Victor de Mello Lecture)

Abstract

At this time, there is a crisis associated with concern over the safety of tailings dams and lack of trust in their design and performance. This crisis has resulted from recent high-profile failures of dams at locations with strong technical experience, conscientious operators, and established regulatory procedures. It is the primary intent of this Lecture to assess the underlying cause(s) for this crisis, review the response to it by various agencies, and to make recommendations on how to overcome it. The Lecture begins with a review of the evolving safety culture associated with slope stability problems as exemplified by the achievements in Hong Kong. This is particularly relevant here because Victor de Mello was a key contributor to the recommendations made in 1976 that initiated the development of the Hong Kong Slope Safety System. The Lecture then addresses the evolution of the safety culture associated with water dams. While there is a long history of concern with respect to water dam safety, these concerns were intensified by several catastrophic dam failures that occurred in the USA in the 1970s. The evolution of regulatory systems from that time is recorded, as is the later trend to adopt risk-based safety assessment and regulation. However, the process that has emerged has been much affected by the Oroville Dam Spillway incident, and dam safety practice is being reassessed by many. This Lecture summarizes some of the major findings arising from the analysis of this incident and makes recommendations to move to more performancebased risk-informed design and safety reviews that are constrained by reliable evidence to a greater degree than is currently the case. Turning to the evolving safety culture for tailings dams, this emerged with rational dam design procedures in the 1970s, more or less as an appendage to water dam design. The growth of environmental legislation related to surface water quality had a considerable impact as well. Hence, a twin regulatory regime emerged in the 1970s. The regulatory regime for tailings dams is typically more regional than national. The failure rate for tailings dams has generally been proportionately higher than water dams and thus has received considerable attention in the technical literature, however without measurable results. The recent failures of major dams in technically advanced regions of the world, operated by mature mining organizations and designed by recognized consulting engineers, has created a crisis in terms of a loss of confidence and trust associated with the design, construction, operation, and closure of tailings storage facilities. Responses to these failures are analyzed, and all are found wanting, particularly since the widespread evidence for weak engineering is inadequately recognized. The Lecture proposes a system for Performance-Based Risk-Informed Safe Design, Construction, Operation, and Closure of tailings storage facilities. It further urges the International Council on Mining and Metals (ICMM) to support the proposed system and facilit...

Risk management for geotechnical structures: consolidating theory into practice (Pacheco Silva Lecture)

“…Since then, acceptance and tolerance curves have been proposed, and more recently they became stricter, more severe, indicating lower risk acceptance by the society. Presently, most risk criteria limit the acceptance zone of one potential life loss (consequence) to a probability of 10 -4 to 10 -5 (FEMA, 2015;Morgenstern, 2018), as shown in Fig. 13, assuming a life loss compensation of R$ 10 million (Brazilian Real -BRL).…”

“…Other institutions in Brazil have also contributed actively to risk management in geotechnical structures, such as the Federal University of Ouro Preto (UFOP), Pontifical University of Rio de Janeiro (PUC-Rio) and University of São Paulo (USP), to cite a few. Lately, this topic has been gaining importance in the Brazilian geotechnical community and widely disseminated by the ABMS, contemplating risk aspects, analysis and management in three Milton Vargas Lectures (Coutinho, 2010;Aoki, 2011;Hachich, 2018), two Pacheco Silva Conferences (this paper; Aoki, 2016) and two Victor de Mello Lectures (Mitchell, 2014;Morgenstern, 2018).…”

The benefits of integrating long-term tailings and mine plans

“…Recently, and more than ever, the mining industry is being increasingly challenged to improve tailings management. The recurrence of tailings storage facility (TSF) failures in recent years has created a crisis in terms of a loss of confidence and trust associated with the design, construction, operation and closure of such facilities (Morgenstern 2018).…”

Guidelines and recommendations on minimum factors of safety for slope stability of tailings dams

“…al., 2019. Morgenstern (2018) stated in the written version of his Victor de Mello Lecture: "At this time, there is a crisis associated with concern over the safety of tailings dams and lack of trust in their design and performance" as well as emphasized during the lecture itself that engineers have to consider that a tailings dam will liquefy if the material deposited is in a contractive condition: "if it can it will [liquefy]". Few countries, like Brazil, took a radical step and legislated to banish upstream method tailings dams, postulating a time framework for all existing upstream dams to be decharacterized, with decharacterization having to follow stricter requirements than decommissioning.…”