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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Sedimentation of reservoirs is acknowledged as a global issue and likely impacts water storage capacity in Australia. This major challenge to our future water supply is a highly complex process with deposition leading to infilling of the reservoir of course sediments in headwaters following major inflows, progressively to finer fractions towards dam walls. Wave action and catchment inflows during drawdown conditions will further transport and redistribute sediments into the main body of the reservoir.
Managing reservoir sedimentation requires an understanding of the sediment types and deposition patterns across the reservoir. Once the location and type of sediment is known, strategies to mitigate the effects on the reservoir can be determined. Methods typically used for determining sedimentation of a reservoir are empirical or modeling techniques that rely on detailed data from inflow events, suspended solids loads and flow rates. In the absence of this data, more direct measurements to quantify the amount of sediment present can be used. Direct measurements are more robust than modelling approaches that utilise rating curves that can result in over estimations of the sediment present. This study combined several measurement techniques to produce high spatial coverage of the reservoir floor. Detailed validation of this approach was undertaken in one representative reservoir prior to adopting this approach across multiple reservoirs.
The purpose of this paper is to document a limited review of the existing concrete chute spillways in the United States Army Corps of Engineers (USACE) portfolio of dams. This internal review was undertaken in response to the partial spillway failure of the Oroville Dam concrete chute spillway in February 2017, the partial spillway failure of the Guajataca Dam concrete chute spillway as a result of Hurricane Maria in September 2017, and to address the request by the United States Congress for USACE, United States Bureau of Reclamation (USBR), and the Federal Energy and Regulatory Commission (FERC) to review their respective portfolios for similar spillway vulnerabilities as Oroville Dam. The intent was to screen for existing concrete chute spillways within the USACE portfolio that may be susceptible to damage/failure during operation.
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.
International emergency agencies such as the Federal Emergency Management Authority (FEMA) in the U.S. highlight a lack of public awareness of hazards relating to dams (FEMA, 2012). This is an issue faced by emergency management agencies around the world, including in Australia and New Zealand. Without hazard awareness, communities who live downstream of large dams are potentially more vulnerable to possible risks, and are likely to be less resilient when hazards arise. One way to address this knowledge gap is risk communication or the meaningful and purposeful exchange of information about risk among relevant parties (Covello, von Winterfeldt, & Slovic, 1984).
This study adopted a mental models approach (see Lazrus et al., 2016) to identify community members’ knowledge of dam failure by comparing their views with those of experts. Data were collected via depth interviews with dam safety experts (n=5) from across Australia, and community members (n=26) living downstream of dams in South East Queensland in Australia. Participants were asked to discuss knowledge about dam failure and to evaluate a dam safety message taken from a U.S. dam authority that was verbally read to them. Interviews were transcribed and analysed to identify the gaps between expert and community member knowledge.
Analysis showed some convergence on general dam operations but, less comprehensive community understanding of the causes of dam failure and dam safety management. Response to the U.S. dam safety message was mixed, with some participants believing it delivered the message appropriately, and others feeling it overstated risk or that its intended use was primarily to protect dam operators. Notably, these varied responses were often related to participants’ level of knowledge of dams. Combined, the findings highlight an opportunity to close the gap in knowledge. These findings will inform the strategies and materials for the South East Queensland bulk water authority Seqwater in engaging with communities downstream of their 26 dams. The research will guide the approach in conveying knowledge with an appropriate tone to support ongoing community engagement activities and increase resilience.
Computational Fluid Dynamics (CFD) is the science of predicting momentum, mass and heat transport, and can aid in design and safety issues for dam resilience in modern settings. Applications of CFD have historically been in the aerospace, automotive and chemical process industries with limited application in the hydraulic engineering field; possibly due to the associated computational intensity that is typically required. However, over the past two decades the cost of computing power has decreased substantially while the processing speed has increased exponentially. These developments have now made the application of CFD in the commercial environment feasible. CFD is particularly valuable in complex flow situations where the outputs required cannot be provided by a traditional hydraulic assessment approach and where there are stakeholder drivers such as service life, insurance cover and safety implications of infrastructure. The need for CFD when these drivers and complex flow situations arise, are demonstrated by means of a case study.
In the case study, CFD was used to investigate the flow patterns and the predicted performance of the outlet pipework from Massingir Dam in Mozambique. Three flow scenarios with appropriate pressure and flow boundary conditions were analysed for the outlet pipework, which included bifurcations for power generation from the main discharge conduits. Specific concerns addressed were, firstly, the possible excessive negative pressure in the region of the offtake for power generation and the potential for cavitation effects and, secondly, unacceptable velocity gradients in the power offtake pipework. Results showed that although some negative pressures were possible in one flow scenario, mitigation measures based on the CFD outputs could be considered and designed before construction.
The implementation of CFD in the above case study displays how risk in design can be reduced to ensure safety issues are addressed effectively.