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2017 Papers
2017 – Haldon Dam Remediation: A Case Study of Earthquake Damage and Restoration
Learn moreJohn Harris, James Robinson, Ron Fleming
Haldon Dam Remediation: A Case Study of Earthquake Damage and RestorationJohn Harris, James Robinson, Ron FlemingAECOM New Zealand LimitedAECOM New Zealand Limited, Fleming Project Services Limited Haldon Dam is a 15m high zoned earth-fill embankment irrigation dam, located approximately 10 km south-west of Seddon, in the Awatere Valley, New Zealand. The crest and upstream shoulder of the embankment suffered serious damage during the 2013 Cook Strait earthquakes, and the Regulator enforced emergency lowering of the reservoir by 5.5m to reduce the risk of flooding to Seddon Township from a potential dam failure. AECOM was engaged by the owner to carry out a forensic analysis of the damaged dam and subsequently the design of the 2-Stage remedial works. The remedial works addressed the existing dam deficiencies and earthquake damage in order to restore the dam to full operational capacity and gain code compliance certification. Key features oft he approach included holding a design workshop with the owner prior to undertaking detailed design, careful rationalisation of the upstream shoulder to optimise the competing interests of strength and permeability, contractor and regulator involvement in the design and construction process, and balancing risk and constructability with the chimney filter retrofit. This paper presents a description of, and approach to, remedial works solution undertaken to remediate a substandard and earthquake-damaged dam to fully operational status in an area of high seismicity. Applying this approach, the objective of achieving a robust, safe, economical design that was acceptable to the regulators and the owner was achieved.
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2018 Papers
2018 – Potential Geologic Sources of Seismic Hazard in Australia’s South-Eastern Highlands: What Do We Know?
Learn moreDan Clark, Andrew McPherson, Brad Pillans, Duanne White, Don MacFarlane
Many mapped faults in the south-eastern highlands of New South Wales and Victoria are associated with apparently youthful topography, suggesting that faulting may have played a role in shaping the modern landscape. This has been demonstrated to be the case for the Lake George Fault, and may reasonably be inferred for the poorly characterised Murrumbidgee, Khancoban, Tantangara, Berridale Wrench and Tawonga faults. More than a dozen nearby major faults with similarly youthful topography are uncharacterised. In general, fault locations and extents are inconsistent across different scales of geologic mapping, and rupture lengths, slip rates and other fault behaviours remain largely unquantified. A more comprehensive understanding of these faults is required to support safety assessments for communities and large infrastructure in the region.
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2019 Papers
2019 – A Novel Solution for Ensuring Post-Earthquake Operability of Outlet Towers
Learn moreCameron Purss, Francisco Lopez, Steve Gray
Earthquake design of a dam and associated appurtenant structures is a key aspect of dam design in the modern era. This paper outlines the design process undertaken to address potential earthquake loading for the 32m high outlet tower to be constructed as part of the new Eurobodalla Southern Storage project on the NSW South Coast. The driver for the project is to provide increased water supply security to communities on the South Coast, an area that is currently serviced by a single reservoir and is subject to frequent water restrictions. Construction is planned to commence for the project in early 2021.
This paper presents the design methodology undertaken to meet the requirements for earthquake design and presents a novel defensive design solution to improve the reliability of the outlet works for post-earthquake operation. The Authors contend that utilising this approach in design of future outlet towers will provide a greater level of confidence in the ability to undertake intervening measures following a severe earthquake. Moreover, the technology has the potential to serve as a relatively inexpensive interim upgrade measure for existing outlet towers expected to sustain an unacceptable degree of damage under earthquake loading.
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2019 Papers
2019 – Nonlinear FE Analysis and Remedial Design of Cracked Dam Monoliths Subject to Large Post-tensioning, Flood and Earthquake Forces
Learn moreFrancisco Lopez , Michael McKay , Jonathon Reid , Nathaniel Selladurai
The Keepit Dam Safety Upgrade Project is being implemented to bring the 54m high concrete gravity dam in line with current guidelines for flood and earthquake loading. Stage 2A of the project involves the installation of two vertical 91 strand post-tensioned anchors on each monolith of the spillway section.
During coring of the anchor head blocks for the vertical anchors, deep cracks were observed across some monoliths, dipping diagonally in an upstream direction. In two of the monoliths the cracks were found to be continuous enough to possibly daylight at the upstream face and form freestanding blocks. If the freestanding blocks postulate is correct, the block stability could be currently relying on the friction of the cracked surface and on the engagement with shear keys of adjacent monoliths, which are provided in the vertical contraction joints.
This paper will explain the complex 3-D nonlinear Finite Element Analysis (FEA) conducted to replicate the conditions of the cracked spillway monoliths during the post-tensioned anchor installation. The nonlinearity captured the expected opening, closing and sliding of the crack, as well as its potential pressurisation, and the residual shear strength retention due to asperities of the crack surface. For the shear keys of the vertical contraction joints, the nonlinearity captured the force-deformation relationship of the plain concrete, up to a brittle failure condition if the shear strength threshold was reached.
The 3-D nonlinear FEA was also used to design the optimum number of Macalloy post-tensioned bars required to stitch the freestanding block to the monolith, so that the vertical anchors can be safely installed. In addition, the remedial design accounted for future extreme design flood and extreme earthquake loading conditions, the latter modelled with a time-history analysis.
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Guidelines
Guidelines for Design of Dams and Appurtenant Structures for Earthquake (July 2019)
Learn moreANCOLD published its first Guidelines for Design of Dams for Earthquake in 1998. The Guidelines were prepared to bring together knowledge about earthquakes in Australia following the devastating
Newcastle (1989 magnitude Mw 5.4) and the Tennant Creek (1988 magnitude Mw 6.6) earthquakes, and improved analytical methods to predict the behaviour of dams subject to earthquake.When the 1998 Guidelines were issued, it was recognised that over time there would be improved data and tools to help the designer. This has indeed been the case and ANCOLD decided that it would be timely to update its Guidelines to incorporate the significant advances made in the understanding of earthquakes, seismic hazard assessments, analysis and design.
The Working Group convened to produce these updated Guidelines, replacing the 1998 Guidelines, was composed of representatives from dam owners, State dam safety regulatory agencies and private consulting practices. The draft Guidelines were made available for comment by ANCOLD members and international review of the Guidelines was undertaken by eminent practitioners in the subject matter from the United States, New Zealand and Switzerland.
Because of the seismic hazard uncertainty and the associated structural response, these Guidelines
encourage the use of risk-based methods for assessing existing dams and for the design of new dams. However, the deterministic approach is also covered for those owners who prefer to use it.This guideline is the culmination of a great deal of voluntary work by convenor, Mr Steve O’Brien and his working group. It is a significant development for dam engineering in Australia and will be a valuable resource.
As with all ANCOLD Guidelines, this guideline is not a design code or standard and has been produced for the guidance of experienced practitioners who are required to apply their own professional skill and judgement in its application. Users must keep abreast of developments in the design of dams and appurtenant structures for earthquake and take those developments into account when using these Guidelines.
The Guidelines will again be reviewed when knowledge and practice have developed to a point when an update is required. Accordingly, ANCOLD welcomes comments from users and other interested parties.
Shane McGrath
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Chairman of ANCOLD Inc.
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2006 Papers
2006 – Specialist Dam Safety Instrumentation for Identifying and Monitoring Earthquake Damage at Aviemore Dam, New Zealand
Learn moreP Amos, N Logan and J Walker
There are a number of geological faults in close proximity to Aviemore Power Station in the South Island of New Zealand, including a fault in the foundation of the 48m high earth dam component of the power station. Possible movement of the Waitangi Fault in the earth dam foundation is of particular concern for dam safety, and the effects on the dam of a fault rupture has been the subject of detailed investigation by the dam’s owner Meridian Energy Ltd. These investigations have concluded that the dam will withstand the anticipated fault displacement related to the Safety Evaluation Earthquake without catastrophic release of the reservoir.
The identification of damage to the dam following an earthquake and monitoring of the dam to identify the development of potential failure mechanisms are important for determining the post-earthquake safety of the power station. The first stage of the post-earthquake response plan is the quick identification of any foundation fault rupture and damage to the dam to enable immediate post-earthquake mitigation measures
to be initiated, such as reservoir drawdown. Following initial response, the next stage of the postearthquake monitoring programme for the embankment dam is longer term monitoring to identify a changing seepage condition due to damage to the dam that might lead to a piping incident. Such an incident may not occur immediately after an earthquake, and it can be some time before the piping process becomes evident.This paper presents some key instrumentation installed at Aviemore Dam and included in the emergency response plan for the post-earthquake monitoring of the embankment dam.
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2007 Papers
2007 – Seismic hazard assessment of the Lake Edgar Fault
Learn moreA. Swindon, M. Gillon, D. Clark, P Somerville, R. Van Dissen and D. Rhoades
The 45 km long Lake Edgar Fault in south-west Tasmania passes through the right abutment of the Edgar Dam and into Lake Pedder, and within 30 km of three other large dams. In 2004 an independent seismotectonic study concluded that the fault had moved three times in the past 48–61,000 years, with the last movement around 18,000 years ago.
In order to better constrain the risk assessment for the nearby dams, the likelihood of a rupture recurrence along the fault was required. Two independent methods were investigated. The first was a comprehensive review of active faulting and deformation of stable continental region faults within Australia, and a comparison with similar faults worldwide with the well studied behaviour of the Lake Edgar Fault. The study results demonstrated the episodic nature of stable continental region fault activity, separated by much longer periods of quiescence, with a decreasing likelihood of rupture following each event within an active period. The time window of applicability of this paleoseismological study is thousands to tens of thousands of years.
The second study looked for evidence of precursory seismic activity in the vicinity of the fault which could indicate an increasing risk of rupture over the next decade or so. This method does not predict specific earthquakes, but does forecast whether the level of future earthquake activity in the short to intermediate term is relatively low, high or at an average level. Using a catalogue of seismic activity for south-eastern Australia, the study concluded that there is no evidence for precursory seismic activity in the area of the Lake Edgar Fault that would give rise to an elevated forecast rate of occurrence of moderate magnitude earthquakes either in the short to intermediate term. This precursory method has a window of applicability of a decade to perhaps several decades.
The combination of these two studies has advanced the understanding of the Lake Edgar Fault activity by both setting it in the long-term stable continental region fault context and investigating the presence of short-term behavioural activity. This has allowed the seismic hazard to be re-assessed as nearer to ambient levels than earlier postulated. This work has applicability for other fault scarps in Australia, both with regards to better defining the long-term hazard (103-105 years) posed by a fault, and potentially also giving advance (short-term 101 years) notification of increasing risk of fault rupture. Better long- and short-term hazard information allows more complete and thorough engineering decisions to be made.
Keywords: Earthquake, seismic, fault rupture, dam safety, risk assessment, Hydro Tasmania, Lake Edgar Fault.
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2011 Papers
2011 – Numerical Modelling of Seismic Liquefaction for Bobadil Tailings Dam
Learn moreB. Ghahreman Nejad, H. Taiebat, M. Dillon and K. Seddon
One of the causes of tailings dam failure has been seismically induced liquefaction during earthquakes. Liquefaction, if mobilised, significantly reduces the stiffness and strength of affected soils in the embankment dam or its foundation and may lead to large deformations and dam failure. This paper reports the results of seismic liquefaction assessment and deformation analyses of Bobadil tailings dam located in Tasmania. The tailings dam consists of a perimeter rockfill starter dam which has been raised in stages using the “upstream” construction method. The embankment raises (formed by clay or coarse tailings) are constructed over a foundation of previously deposited tailings in the impoundment which is potentially susceptible to liquefaction. Extensive field and laboratory tests were carried out to assess the tailings liquefaction potential and also to determine the material properties required for seismic stability and deformation analyses. Numerical modelling of seismic liquefaction and deformation analyses were carried out to predict the magnitude and pattern of deformations that may lead to uncontrolled release of tailings. The results of these analyses are presented and compared with literature report of those observed during past earthquakes.
2011 – Numerical Modelling of Seismic Liquefaction for Bobadil Tailings Dam
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