Meizhiwen Zheng, Nimal Gamage
This study used MIKE 21 to replicate the Cooma tank failure by varying modelling input parameters. This study explores the mechanism by which flood water can damage buildings and investigated different damage category assessment method to predict building damages.
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Now showing 1-12 of 37 3483:
Dr Mark Leonard
The quantification of the 85% and 95% hazard fractiles, as required by the ANCOLD 2019 Guidelines for design of dams, is investigated. It is found that there are four independent sources of uncertainty in the PSHA input models that have a significant effect on the hazard. So all four need to be quantified, particularly for Extreme and High A consequent dams. It is also found that the uncertainty of many of the other parameters, which are routinely included in probabilistic seismic hazard assessments, have minimal effect on either the mean or the higher fractiles so do not necessarily need to be routinely included. The complexity of the input models required to satisfy the new standards are substantially higher than those routinely used in prior decades.
Ryan Singh, Jiri Herza, James Thorp, Michael Ashley
Performance-based risk-informed decision making is an underlying principle of the Global Industry
Standard on Tailings Management (GISTM). While owners make significant efforts to align with this
principle, commonly used risk assessment and management practices in the mining industry have largely been based on the HSE principles, which consider more frequent, lower consequence incidents.
As a result, the existing risk assessment frameworks do not provide the owners with a comprehensive understanding of the risk profiles of their tailings storage facilities (TSFs). Without the understanding of a facility’s risk profile, the owners cannot appreciate how changes to their facility, processes and operational activities may impact the risk profile. A large step-change in thinking is therefore required in risk assessment practices for the owner to align their TSF management with GISTM requirements.
Beyond risk assessments, the mining industry has other valuable concepts to manage the safety of their tailings management practices, such as Critical Controls, however, commonly used risk assessment and management practices do not incorporate these concepts.
This paper explores commonly used risk assessment practices and the concepts of Critical Controls. It proposes how these concepts can be linked, with Critical Controls being embedded in the risk assessment process. The outcomes of linking these concepts result in an estimation of the effectiveness of the Critical Controls and how they can be improved to demonstrably reduce the risk presented by a TSF. A case study has been included to demonstrate the benefits of linking risk assessment with Critical Controls and how owners can readily identify deficiencies and efficiently manage the risk profiles of their facilities.
Jonathon Reid, Brendan Trebilco
The dam reviewed was designed and constructed in two stages, with the embankment completed in 1965. The dam comprises a 37 m high earth and rockfill maximum section on the creek alignment and zoned earthfill embankments of varying arrangements on the abutment flanks with a total crest length over 2km.
A Dam Safety Review was undertaken as part of the owners on-going commitment to maintain its portfolio of dams in a safe and functional state. The dam has suffered from high seepage rates that were first observed in 1971 after the reservoir rose to a historic high level, which was then exacerbated in 2011 after the reservoir rose a further 10m to reach the Full Supply Level for the first time. Reviews of the embankment stability at this time resulted in operating restrictions being placed on the reservoir level.
Detailed instrumentation data collected over a range of filling events showed the rock foundations to be highly responsive in the areas of observed seepage. This resulted in rapid pore pressure responses in foundation soils and the lower portion of the embankment after a rise in reservoir level, but a much slower pore pressure response in the upper parts of the embankment.
Seepage and stability analyses were undertaken based on the high quality instrumentation data to review the stability of the sections for various operating levels and with projected pore pressure increases for rapid flood loading scenarios. The paper explores the sensitivity of the analyses completed and how different construction standards applied to varying sections on the same embankment resulting in acceptable and undesirable outcomes.
Chris Nielsen, Ron Guppy, Donna Dunn, David Murray
Following several years of investigations and analysis a serious safety issue with the stability of the primary spillway during major flood events was identified at Paradise Dam that required urgent risk reduction works. The response to this safety issue was significant.
The Inspector General Emergency Management conducted a review into the effectiveness of emergency response if a dam safety event were to occur, taking into consideration process and communications to manage around 40,000 population at risk, comprised mostly of residents within the city of Bundaberg.
An essential works program to reduce the risk was urgently prepared then executed effectively within a calendar year. This short timeframe required significant and novel amendments to Queensland’s laws to bypass normal legislated process for such a major project.
The Paradise Dam Commission of Inquiry was established to identify the root cause of the issues, the facts and circumstances that contributed to them and recommendations to consider for future dam projects. All recommendations from the commission were accepted by the Queensland government and, following an extensive stakeholder engagement exercise, have been implemented through changes in policy and methodology and described in published guideline revisions.
For future dam projects the lessons learnt highlighted the need for early and ongoing engagement of
independent technical review, project governance that is cognisant of risk and the ownership and capacity to bear of that risk, the need to consider testing to confirm critical design parameters and the need for an effective regulator. The essential works program has established a precedent for the timely and appropriate application of risk reduction measures.
Jonathon Reid, Mark Sinclair
Large concrete piers supporting gates on spillways can be impacted by earthquake loading and often found deficient in cross-valley loading. However, piers can also be susceptible to damage from upstream-downstream seismic loading and from additional pressures from increased flood loading requirements. This can have detrimental impacts on the connection of the pier with the main dam body. In recent years, a number of projects have required spillway piers to be upgraded by post-tensioning into the dam body with large multistrand anchors, up to 65 strands, to prevent failure mechanisms (bending, shearing, rocking) from forming and causing serious damage. These, often very short anchors, present special design and construction challenges that are explained in this paper. This situation also often requires the anchors to be very closely spaced with bond zones overlapping. Case examples demonstrating potential limitations in the design of spillway pier anchors and the different requirements to the more usual vertical post-tensioning of a dam body are presented.