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.
Design floods for most dams and levees typically have an annual exceedance probability (AEP) of 1:100 (1E-2) or less frequent. In the U.S., high hazard dams are designed to pass the Probable Maximum Flood (PMF), which typically has an AEP of 1:10,000 (1E-4) or less frequent. In order to reduce epistemic uncertainties in the estimated AEP for extreme floods, such as the PMF, it is important to incorporate as much hydrologic information into the frequency analysis as reasonably possible. This paper presents a Bayesian analysis framework, originally profiled by Viglione et al. (2013), for combining at-site flood data with temporal information on historic and paleofloods, spatial information on precipitation-frequency, and causal information on the flood processes. This framework is used to evaluate the flood hazard for Lookout Point Dam, which is a high priority dam located in the Willamette River Basin, upstream of Portland, Oregon. Flood frequency results are compared with those from the Expected Moments Algorithm (EMA). Both analysis methods produce similar results for typical censored data, such as historical floods; however, unlike the Bayesian analysis framework, EMA is not capable of incorporating the causal rainfall-runoff information in a formal, probabilistic manner. Consequently, the Bayesian method considered herein provides higher confidence in the fitted flood frequency curves and resulting reservoir stage-frequency curves to be used in dam and levee safety risk assessments.
The development of geological, engineering geological and geotechnical models is essential for all dams. These models provide the basis for understanding the engineering characteristics of foundation materials and geological structures that are critical to the safe design, construction and operation of the dam.
The use of digital three dimensional (3D) engineering geological modelling techniques is becoming more common for civil infrastructure projects. In addition to established design applications, 3D engineering geological models can be utilised by dam owners, operators and stakeholders for ongoing management of the dam.
The recent option studies at North Pine Dam in Brisbane, Australia, provides an example of collaboration between the owner (Seqwater) and the designer (GHD) to maximise the use of existing information and to enable future information to be efficiently integrated and utilised.
The initial North Pine Dam 3D engineering geological model was developed using historical records dating from the design and construction of the dam in the 1950’s and 1960’s. These records had been carefully stored, collated and digitised by the owner, so that they could be easily georeferenced and incorporated into the 3D engineering geological model.
The initial model was interrogated to identify data gaps and to plan targeted and cost-effective investigations that addressed critical geotechnical issues. The 3D engineering geological model was further refined using the newly acquired data, to develop a comprehensive “3D database” that can be used to visualise and interrogate all existing records as high- resolution georeferenced images and embedded data.
This provides an asset for the dam owner to maximise the use of existing information and reduce the cost of future safety reviews or design.
As predicted by Powel (2000) claims for professional negligence are very common and their frequency is increasing due to the increasing demand for professionals’ services, specialisation, higher standards, intolerance of poor performance by societies and the increasing litigious nature of business.
The increasing expectations of the society are reflected in the changing attitude of the authorities and courts towards professionals when things go wrong. The changing attitude is fuelled by the unprecedented media coverage of failures of structures with human and environmental losses. This is particularly relevant to the tailings industry, which is marked by the recent dam failures in Canada, Brazil, Mexico, China, Australia and India.
The far reaching expectations for duty of care of professionals has been strikingly illustrated from the fallouts from recent major and widely publicised TSF failures such as Mt Polley (three consultant engineers accused of unprofessional conduct), the 2015 Samarco failure (22 individuals charged with various criminal offences including homicide) and the recent Brumadinho failure (charges of false representation have also been brought against the consultant engineers).
This paper examines the responsibilities and duties of engineers operating in the tailings industry with respect to the professionals’ duty of care and the consequences of breaching those responsibilities and duties. This paper also discusses the potential conflicting interests of consulting engineers and proposes that engineers are, in the vast majority, ill-prepared for navigating the changing waters of professional negligence.
The authors of this paper believe that a better understanding of the professional duty of care could reduce the number of claims for professional negligence. As a corollary, the reduced rate of professional negligence could result into fewer tailings failures in the future.
Professional industry bodies such as Engineers Australia should act to clarify the legal obligations and duties of engineers, as they are the best placed institutions to do so for the whole industry. In addition, consideration should be given to inclusion of a discussion of the aforementioned obligations and duties into relevant ANCOLD Guidelines.
The paper evaluates the stability of the reinforced rockfill at the downstream side of Waimea Dam, a new CFRD dam that is currently under construction in New Zealand. The reinforced rockfill is part of the overall diversion strategy for the dam during construction and has been designed to allow for safe overtopping to a depth of 2.9m, which corresponds to the 1 in 1,000 AEP flood.
Design of reinforced rockfill for overtopping allows for the safe passage of floods that exceed the capacity of the primary diversion works. This may be required for dam safety during construction, as is the requirement for Waimea Dam. It also serves to protect the works whist the dam is being built.
The focus of the paper is the stability assessment of the reinforced rockfill to prevent seepage induced instability during overtopping. As seepage forces have a considerable effect on the stability of the dam, a finite element seepage analysis was undertaken to estimate the seepage forces throughout the embankment, which was used in the design of the reinforcement system.
Details of the design process, including the seepage and stability analysis for a range of configurations are outlined, and recommendations for the design of similar future projects are provided.
As part of the development of some dams and hydroelectric power schemes, deep infrastructure is often required which requires and understanding of the in situ stresses of the rock mass. Recent works completed in southern Australia and Europe have led to improved methodologies for conducting effective, reliable, and repeatable measurements of in situ strain and/or deformation, as well as the subsequent estimation of in situ stress.
In situ stress testing is generally an item that is specified as part of a geotechnical investigation, however it is not commonly well understood in terms of reliability, repeatability, or, in fact, what the result actually means and its implications to project design. Commonly, a handful of tests are completed, with variable results, which often generates more confusion than answers.
This paper provides a discussion of recent in situ stress testing completed for two deep Australian projects. It summarises the aim of the investigations, test selection process, laboratory testing, data review and model development. This is to illustrate how complex the estimation of in situ stress can be and some of the pitfalls that may be avoided whilst acquiring and assessing the data. It also examines several different testing methods available in the Australian and International industry and some of the analysis techniques available to dam and tunnel projects. Finally, the paper provides an update on topical developments provided at recent workshops in Europe.