Paul Somerville, Andreas Skarlatoudis, Jeff Bayless, Polly Guan
The 2019 ANCOLD seismic guidelines state that “A hazard assessment should be conducted for earthquake magnitudes Mw 5 and above. However, under certain circumstances, smaller magnitude earthquakes may form the lower limit. With masonry dams, slab and buttress dams, older concrete dams, and structural concrete components of dams, Mw 4 earthquake magnitudes should form the lower limit.” However, when using probabilistic Uniform Hazard Spectra (UHS) with Mmin less than 5.0 per the 2019 ANCOLD Guidelines, the hazard will be overestimated unless Conditional Mean Spectra (CMS) are used to represent the ground motions. As described by Somerville et al. (2015), use of the UHS can significantly overestimate the seismic hazard levels presented by individual earthquake scenarios because the UHS envelopes the ground motions from multiple earthquake scenarios in one spectrum. This overestimation is especially true of the ground motions from small magnitude earthquake scenarios. The probabilistic UHS may have large short period ground motions with contributions from a range of scenario earthquakes, but if the UHS is used as the design spectrum, these ground motions will often be represented by earthquake scenarios having inappropriately large magnitudes, long durations, and high long period ground motion levels. As a result, these design ground motions have the potential to overestimate the response of the structure under consideration. By using CMS spectra and time histories, the large probabilistic peak accelerations, predominantly from small earthquakes, are better represented by earthquakes having appropriately small magnitudes, short durations, and lower long period ground motion levels, yielding more realistic estimates of the response of the structure.
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Gideon Steyl, Ralph Holding, Lis Boczek
A Monte Carlo method for assessing liner systems is applied with outcomes demonstrating the range of discharge that could occur over the liner interface. The Monte Carlo approach allows for variation of fill material over the liner system and includes the assessment of a second compacted zone either above or below the liner zone. In this paper clay liners were evaluated due to regulatory guidelines and it could be demonstrated that similar performance to a 1 m clay liner could be attained using compacted material to reduce discharge over the liner interface. The approach applied in this paper allows for at least a worst-case quantification of seepage risk which could be included in liner selection criteria or presenting liner options to regulators.
Shane McGrath, Mark Arnold, Josh Rankin, Gavan Hunter
Greenvale Dam is a critical storage for the supply of potable water to Melbourne. The dam had been upgraded through current risk management techniques, and an ALARP assessment completed at that time. However, it was decided that a more comprehensive demonstration of ALARP was warranted to satisfy the dam owner’s duty of care. Since there is no comprehensive guidance in the dams industry for owners and their advisors to reference, the safety case approach used extensively in other hazardous industries was adopted. Considering the approaches used by Victoria’s Worksafe, the Institution of Engineers Australia and the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA), the key components of the safety case for Greenvale dam were identified then developed to provide a logical, structured and comprehensive argument for the safety of Greenvale Dam. This paper provides an overview of components of the safety case developed for Greenvale Dam, the use of safety cases for dams and where process improvements could be made.
Neeta Arora, Prashant Agrawal, Yogendra Deva, Ravi Kumar
The tectono-lithologic complexities and the accompanying extreme mass wasting processes make the Himalaya a difficult terrain for river valley development projects envisaging dams and other diversion structures. Besides exceptionally thick riverbed deposits leading to management of deep foundations, abutting the dams often poses challenges in view of difficult ground conditions. The paper looks at three scenarios where the presence of highly decomposed strata, slumped mass and unconsolidated riverbed material led to serious problems in abutting the dams and invariably delayed the project completion. The design approach to special abutment issues is discussed in the light of investigations, explorations, laboratory and field tests, etc. In conclusion, while dependable engineering geological mapping and assessment is considered the backbone, innovative investigations and engineering play crucial role in successful implementation of projects.
Richard M Robinson, Siraj Perera, Gaye Francis
Due diligence has become endemic in Australian legislation and in case law, to the point that it has become, in the philosopher Immanuel Kant’s terms, a categorical imperative. That is, our lawmakers seem to have decided that due diligence is universal in its application and creates a moral justification for action. This also means the converse, that failure to act demands sanction against the failed decision maker.
This applies to dam safety management which represents the archetypical high consequence – low likelihood event. It is now essential to have positively demonstrated safety due diligence in a way that can withstand post-event judicial scrutiny. Presently the only way this can be done is by using the notion of criticality and precaution, not hazard and risk. The test is not that of risk acceptability (as low as reasonably practicable or ALARP), rather it is that no further reasonably practicable precautions (so far as is reasonably practicable or SFAIRP) are available, and that what results is not prohibitively dangerous.
This paper will document the difference between the two approaches and how to positively demonstrate safety due diligence. It also discusses the definition of ALARP as stated in ANCOLD’s Guidelines on Risk Assessment 2003 and the relevance of the safety case principle for dam safety management.
Ryan Singh, Jiri Herza, James Thorp
Recent and continual failures of tailings storage facilities (TSFs), often resulting in catastrophic consequences, has led to calls for action from the industry, stakeholders and the public at large. Several standards and guidelines are being prepared at the time of writing, most notably a Global Industry Standard on Tailings Management (GISTM), with the overall objective to reduce the rate of TSF failures globally. While better guidelines are certainly necessary, there are requirements that must be carefully followed in developing a document that has the ambition to become a standard. If such requirements are not fulfilled, the document can become ineffective or potentially have the opposite result to that which was intended. This paper discusses whether or not the GISTM meets the requirements of the standards and analyses the potentially negative impacts of its implementation on the industry and wider society. Based on this analysis, this paper provides several recommendations for improvements that should be considered by the GISTM panel and other working groups preparing standards and guidelines.