2018 – Revision of Queensland’s Failure Impact Assessment Guidelines
Chris Nielsen, Gary Hargraves, Ron Guppy, Rob Fowden, Peter Allen
In 2018, DNRME released the latest revision of the Failure Impact Assessment (FIA) Guidelines and the first significant change since 2003. An FIA is the instrument for determining if a dam is referable and therefore regulated for dam safety purposes in Queensland.
The guidelines reflect upon changes in legislation and advances in methods and tools for assessing consequences of dam failure. The revised version tends to be less prescriptive and emphasises the responsibility of the engineer completing the assessment to develop appropriate and defensible methods.
The paper provides an overview of the FIA guidelines, key concepts, the steps to follow when preparing an FIA and a comparison to ANCOLD’s latest consequence assessment guideline.
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2018 Papers
2018 – Dam Safety Management of Junction and Clover Dams: A Risk Based and Observational Approach
Learn moreSteven O’Brien, Christopher Dann, Timo Mantyvirta
Junction and Clover Dams are central spillway slab-and-buttress dams located in Victoria. Previous safety reviews and assessments of the dams concluded that neither dam met modern dam design standards and remedial works were recommended, including infilling the slab-and-buttress dams with mass concrete to sustain seismic loadings. These conclusions were based largely on the assessed seismic hazard at the site, the results of response spectrum analyses and observed conditions of the dams including alkali-aggregate reaction of the concrete. AECOM used current seismic hazard assessment techniques, conducted concrete investigations and testing, assessed long term surveillance monitoring results and used modern finite element techniques to demonstrate that no upgrade works were required at either dam resulting in a significant saving for AGL.
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2018 Papers
2018 – What Happened at Oroville Dam and Why – Findings of The Spillway Incident Forensic Investigation
Learn moreJohn W. France, Irfan A. Alvi, Peter A. Dickson, Henry T. Falvey, Stephen J. Rigbey, John Trojanowski
On February 7, 2017, the gated service spillway (also known as the Flood
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Control Outlet or FCO Spillway) at Oroville Dam was being used to release water
to control the Lake Oroville level according to the prescribed operations plan.
During this operation, the service spillway’s concrete chute slab failed, resulting
in the loss of spillway chute slab sections and deep erosion of underlying
foundation materials. Subsequently, as the damaged service spillway was
operated in an attempt to manage multiple risks, the project’s free overflow
emergency spillway was overtopped for the first time since the project was
completed in 1968. Significant erosion and headcutting occurred downstream of
the emergency spillway’s crest structure, leading authorities to evacuate about
188,000 people from downstream communities. -
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2018 Papers
2018 – Comparison of EZ-FRISK and OpenQuake Seismic Hazard Programs
Learn moreElodie Borleis, Russell Cuthbertson
There are a number of software packages that have been developed to conduct Probabilistic Seismic Hazard Assessments (PSHA’s). Each one has advantages and disadvantages. Two such programs are compared; the licenced subscription-based EZ-FRISK software package developed by Fugro USA Land, Inc. and the open-sourced OpenQuake-engine (OQ) software package by the Global Earthquake Model (GEM) Foundation. Both of these packages use the classical PSHA methodology as described by Cornell (1968) and modified by McGuire (1976). Each of these packages offers different advantages; OQ is freely distributed, code based and provides easy access to a number of tools. EZ-FRISK doesn’t rely on command-line tools and instead provides an easy user interface with quick access to plots to check results. EZ-FRISK is computationally faster than the OQ program.
A simple rectangular source model with four sites was used to investigate the degree of agreement between these two software packages. Results indicate that hazard estimates from the two packages agree to within 4% for the two closest sites. At long return periods for the two furthest sites, the difference is larger.
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2018 Papers
2018 – Advances in the Automation of Population at Risk Quantification for Dam Failure Consequence Assessment
Learn moreMatthew Scorah
Population at Risk (PAR) estimation involves quantification of people who could be exposed to flooding in the event of a dam failure. Conventionally, estimates of PAR involve manual and subjective assessment of individual structures located downstream of dams. To reduce the reliance on subjective judgement and better leverage publicly available population datasets, an automated method of PAR assessment was developed. This approach used the Geoscape dataset of building representations to disaggregate Australian Bureau of Statistics 2016 Census data for a study area around Gawler, South Australia.
Representative day and night spatial distributions of PAR were constructed to characterise the diurnal movement of people between homes and workplaces or other day activities. Flows of people were directly quantified to reduce reliance on high level assumptions regarding exposure. A Random Forest model was used to filter sheds and other unpopulated structures from the Geoscape dataset.
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The largest deficiency in this approach is the lack of high detail data to classify building usage. It is recommended that the potential for automation of PAR assessment be continually revisited as more datasets become available. -
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2018 Papers
2018 – Probability of Surface Faulting from an Earthquake Affecting a Vulnerable Structure
Learn moreRussell Cuthbertson and Leanne Capewell
While structures such as a dam walls, pipelines, gas storage tanks, and nuclear facilities are vulnerable to the shaking from earthquakes, they are even more susceptible to differential movement on faults passing beneath their foundations.
In the past, the probability of surface rupture of a fault was calculated by making some simplistic assumptions about the distribution of earthquake magnitudes. Improved databases of earthquake ground faulting now allow the probability of surface rupture to be estimated in a more realistic fashion. Computing software that uses a Monte Carlo approach has been developed to allow the effect of various scenario choices on rupture probability to be investigated.
Using this software, it is found that the most significant influence on rupture probability is the long-term fault slip-rate. Other assumptions about the faulting style, maximum magnitude and conversion parameters have only a moderate influence on the results.There have been several instances in recent history in Australia of surface faulting due to earthquakes, but there has been only limited damage to infrastructure due to the remoteness of these earthquakes. The software that has been developed will allow a considered assessment and comparison of the hazard and risk due to both ground shaking from earthquakes and from surface rupture.
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