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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Many numerical simulations have tried to model the failure-induced displacements of earth structures due to liquefaction. In this paper, the challenges in modelling such as the large displacement and non-immediate failure of earth structures due to liquefaction are discussed. An advanced bounding surface plasticity model is used to simulate the dynamic behaviour of saturated porous media. A series of benchmark welldocumented seismic events are analysed, and the results are compared to the reported laboratory and field observations. These analyses consist of one centrifuge test on liquefiable sand (Model #12 of the VELACS project) and one earthfill dam (Lower San Fernando Dam in California) subjected to seismic loading that leads to liquefaction. The capability of the model to capture the flow failure due to liquefaction is demonstrated and results are compared with other attempts in the literature to capture similar responses.
Identification of people impacted by a hypothetical dam-break flood is required to understand the potential hazard a dam poses to downstream communities. The New Zealand Dam Safety Guidelines and the Australian Consequence Categories for Dams define these people collectively as the “Population at Risk” (PAR) and recommend that evaluation of PAR should include both permanent and temporary populations. However, there is limited guidance on specific methods to determine these populations. This paper provides an outline of an evidence-based, repeatable method to determine the PAR (both permanent and temporary) within a dam-break flood inundation zone. The method is intended to provide guidance for people tasked with estimating PAR in accordance with the New Zealand Dam Safety Guidelines. The methodology provides a current practice framework for users to apply and estimate the PAR in a clear and defendable manner.
Recent tailings dam failures have led to worldwide alarm that we are still getting an average of two
significant tailings dam incidents a year. This is despite the efforts of various industry organisations aroundthe world to raise the standards of tailings dam management. Clearly, a significant number of mining dams are not re silient enough to ensure the required level of safety for sustainable mining operations in a modern world in which there is increasing concern for the environment. This paper updates ANCOLD with international developments in attempting to address shortcomings in the mining industry that is allowing these failures to continue to occur.
In Australia, ANCOLD have released an addendum to the 2012 ANCOLD Guidelines on Tailings Dams, Planning, Design, Construction, Operation and Closure, to coincide with the new ANCOLD Guidelines for Design of Dams and Appurtenant Structures for Earthquake. This addendum also addresses issues of governance of tailings dams and provides additional guidance on the serious issue of static-liquefaction, a critical factor in recent failures.
On the international scene, ICOLD is progressing a Tailings Dam Safety Bulletin that is hoped will set
minimum standards for Tailings Dams for all member countries. In addition, the International Council of Mining and Metallurgy (ICMM) similarly wants to establish an international standard. It is likely that these international bodies will cooperate to ensure a consistent set of guidelines and that countries will accept and implement these.
This paper updates the ANCOLD position regarding guidelines and describes the state of various
international guidelines following the June ICOLD meeting in Ottawa.
Following the failure of Paloona Dam’s intake trashrack during the 2016 floods in northern Tasmania, a replacement trashrack and support structure was designed, manufactured and installed (by diver) within five months. This was a remarkable feat and hailed as a success at the time.
The euphoria, however, was short lived. A routine dive inspection in January 2018 revealed cracked
trashrack bars on one of the panels and this was after less than twelve months’ operation. This prompted a rigorous investigation where it was determined that the bars suffered fatigue due to flow induced vibration. Indeed it is possible that the bars cracked within a few weeks of returning to service.
The science of flow induced vibration is relatively mature, having been extensively researched over several decades. Its application to trashracks is well documented. However, this experience has shown that the common design approach overly simplifies the fluid-structure interaction. For Paloona, the result was a trashrack design which has proven to be inadequate, not having the resilience required for a dam outlet works component.
This paper revisits flow induced vibration theory as it pertains to trashracks, outlines the findings of vibration testing at Paloona, and suggests a design approach which will avoid similar issues. It is hoped that similar failures can be prevented and the design life expected of trashracks achieved.
There are currently around four new flood detention reservoirs (retarding basins) built each year in UK, which although only being modest structures with median height of 4m and reservoir capacity of 300,000m3 pose a significant risk to the community as they are located immediately upstream of the community they are protecting. These communities range from around five to several thousand households.
The cost and therefore viability of these structures can vary depending on the number of defensive features built into the design, which raises interesting conflicting issues of public safety contrasted to vulnerability to property inundation in operational (say, 1 in 100 chance) floods.
The authors have designed and supervised over 30 flood detention reservoirs in the UK in the last 20 years. This paper describes the engineering decisions which need to be made regarding defensive measures and the resilience of these structures to withstand flood loading on demand. Examples of measures to include resilience are described, with discussion of when selection of the options to increase resilience against a particular failure mode should be mandatory, and when it may be more appropriate to consider it on a case by case risk-based approach. The paper will also discuss more strategic issues of how to balance making flood detention reservoirs affordable, while at the same time maintaining high standards of public safety and compares Australian and UK approaches.