Kyle Smith, David Reid, Riccardo Fanni
The estimation of in situ state parameter, Ψ, is a critical part of the characterisation of tailings storage
facilities (TSFs) for the purpose of liquefaction screening and stability assessments. The cone penetration test with pore pressure measurement (CPTu) supplemented by laboratory testing form the current state of practice tools to assess in situ Ψ. Recently, cavity expansion-based CPTu inversion methods, in particular the NorSand Widget, have achieved routine adoption for many engineering applications including TSFs. However, application of cavity expansion-based methods is not without limitations; most notably, cavity expansion-based methods rely upon extensive material specific calibrations, therefore, the results of such methods are limited to the specific soil stratum to which they are calibrated. Additionally, partially drained conditions developed during CPTu are not explicitly considered in currently available methods.
In order to overcome these limitations, this paper presents a generalised method to interpret Ψ from either drained or undrained CPTu, based upon material-specific CPTu calibrations obtained from the NorSand Widget. Guidance on interpretation of drainage conditions developed during CPTu is provided to assist in application of the method. As the method is based upon the NorSand Widget, the influence of elastic soil rigidity is explicitly considered; therefore, the method does not suffer from stress level bias common in screening level methods for estimation of Ψ.
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Ryan Cantrill, Petros Armenis & Angus Cannon
Large Australian dams span a range of ages and were designed and constructed to the prevailing
standards and practices of the day. Since that time, there has been a veritable explosion in monitoring and surveillance technologies available to dam owners to assist with risk management of their portfolio. Coupled with this has been the formalization and ongoing development of regulatory frameworks across the industry.
This paper endeavours to share Sunwater’s recent experience on this topic. Specifically, the following question is considered – how best to apply modern monitoring and surveillance technologies to manage dam safety risks associated with decades old structures, all while still meeting regulatory requirements? In answering this question, the authors necessarily had to consider several inputs including – physical condition of the existing assets; analysis of existing controls and mitigation measures; risk assessment and risk profile of the assets; and operational constraints. As always, outputs invariably required the prioritization of recommendations.
While dam owners must strive to comply with a standard and accepted way of managing their portfolio, it is vital they recognize and address the unique risks that each structure presents. It therefore follows that owners must be prepared to allow the time and provide the necessary resources when formulating a monitoring and surveillance program commensurate with the dam safety risk that their respective portfolio presents
Hench Wang, Edward Funnell, Albert Shen, Matt Scorah, Peter Hill
The use of simulation models to assess dam failure consequences has progressively advanced in Australia over the past few years. For example, it is now common for HEC-LifeSim to be used to estimate potential loss of life from the failure of large dams with large populations at risk downstream. Since its introduction to Australia, numerous presentations and papers have been provided by USACE and industry professionals that highlight the benefits of using HEC-LifeSim Version 1.0.1 for a range of different case studies.
This paper identifies some of the new features in the latest version of HEC-LifeSim that can improve the robustness and defensibility of the potential loss of life estimates for dambreak consequence assessments. The techniques that have been used to overcome these challenges are also discussed using some case studies.
The first case study demonstrates the sensitivity of the model performance and potential loss of life to changes in version and number of iterations used to simulate the life loss. This is done by comparing the differences in simulation run time and life loss between the previous and new versions of HEC-LifeSim for an example model. The second case study presents an example application of both versions of HEC-LifeSim to compare the results between one version and the other for a different dam and the final case study illustrates an improved method for interrogating the available outputs from HEC-LifeSim to provide the user with more information that otherwise could not be obtained from the default outputs.
Zara Bostock, Helena Sutherland
Ewen Maddock Dam is located approximately 12.0 km west of Caloundra, in the Sunshine Coast area of Southern Queensland. The dam is a homogeneous earthfill embankment dam 10.5 m high and 724 m long. The dam was originally built between 1973 and 1976 and later upgraded in 1982 to raise the ogee spillway crest by 2.44 m to the current Full Supply Level (FSL) of 25.38 m AHD.
Seqwater is undertaking a staged upgrade of Ewen Maddock Dam to address deficiencies identified during the Acceptable Flood Capacity (AFC) Review (GHD, 2010). The consequence category assigned to Ewen Maddock Dam is ‘Extreme’ with a downstream Population at Risk greater than 1000.
Stage 1 construction was completed in 2012 to manage the seepage underneath the dam to reduce the risk of piping and improve embankment stability. Stage 2A involved retrofitting a filter in the existing embankment and raising the dam 1.61 m to 30.11 m AHD using a reinforced concrete parapet wall. Stage 2B involves spillway upgrade works and was split from 2A due to approval constraints.
Stage 2A construction was completed in April 2021, navigating various project and dam safety challenges. This paper presents some practical ways dam safety and risk was managed on the ground from the perspective of both the designer and owner.
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.
Dan Clark, Joanne Stephenson, Trevor Allen
We present earthquake ground motions based upon a paleoseismically-validated characteristic earthquake scenario for the ~ 48 km-long Avonmore scarp, which overlies the Meadow Valley Fault, east of Bendigo, Victoria. The results from the moment magnitude MW 7.1 scenario earthquake indicate that ground motions are sufficient to be of concern to nearby mining and water infrastructure. Specifically, the estimated median peak ground acceleration (PGA) exceeds 0.5 g to more than ~ 10 km from the source fault, and a 0.09 g PGA liquefaction threshold is exceeded out to approximately 50-70 kilometres. Liquefaction of susceptible materials, such as mine tailings, may occur to much greater distances. Our study underscores the importance of identifying and characterising potentially active faults in proximity to high failure-consequence dams, including mine tailings dams, particularly in light of the requirement to manage tailing dams for a prolonged period after mine closure.