Simon Lang, Chriselyn Meneses, Peter Hill, Kristen Sih
In Australia to date, the empirical method developed by Graham (1999) is the most widely applied approach for estimating loss of life from dambreak flooding. However, as the move to risk-based approaches of dam safety management has gathered momentum internationally, increasingly sophisticated techniques for estimating loss of life have emerged. One of these models is the United States Army Corps of Engineers (USACE) HEC-FIA model. HEC-FIA models the influence of flooding, structure characteristics, and warning and evacuation assumptions on loss of life in a spatially distributed manner. In contrast to Graham (1999), HEC-FIA also allows the user to model the loss of life for both dambreak and natural flooding.
This paper presents the results from the first Australian application of HEC-FIA to two dams in southeast Australia. The application of empirical methods developed by Graham (2004) and Reiter (2001) is also discussed.
T. Mortimer, J. McNicol, P. Keefer, W. Ludlow
CS Energy’s Kogan Creek Coal Mine located in the Surat Basin in Queensland, services the 750MW coal fired, Kogan Creek Power Station. Strip mining generates large volumes of mine waste which is typically used to construct waste dumps. Recent work at the mine has focused on using mine waste to construct an ash storage facility to store ash that is piped over 5 km from the power station as a dense phase slurry. The use of mine waste to construct the ash storage facility provides significant cost and time savings, however a range of design, construction and operation issues needed to be addressed to operate a facility of this type.
This paper describes some of the key design, construction and operation considerations for the ash storage facility. Design considerations include pipeline transport through environmentally sensitive areas, addressing the stability of the embankment and the use of a partial LLDPE geomembrane lining system to reduce the risk of seepage from the storage. Construction considerations include post construction (pre ash deposition) floor treatment to reduce potential settlement. Operational considerations include ash slurry deposition, water management of the decant pond and progressive rehabilitation of the final landform.
2011 – Design, Construction and Operation of a Partially Lined, Ash Storage Facility Constructed from Mine Waste
Bob Wark, Alex Gower, Paul Hurstand Sofia Vargas-Pedroza
ANCOLD has been working towards setting up guidelines for outlet works and has a standing committee that is addressing this issue. Recent papers have addressed the issues of current technical practice. However the authors believe that there is a sufficient body of experience available from recent incidents to provide a valuable tool that the guidelines can use to address the issues that are important. The authors have identified almost 40 incidents with outlet works that have occurred over the last 40 years, many of them within the last 20 years and have tabulated them as part of this paper. These range from the interesting to those that can and have threatened worker safety and life. The paper outlines the most significant of these and summarises the causes and corrective action necessary.
Horror Stories with Outlet Works
R.J. Nathan, P.I. Hill, and P.E. Weinmann
The current definition of the Probable Maximum Flood (PMF) is open to subjective interpretation, and this lack of objectivity can lead to inconsistencies in the application of risk-based and standards-based criteria. This paper summarises the different approaches used to estimate the PMF, and highlights how these reflect differences in the availability of design information and local tradition and experience. A number of approaches are available that can aid the objective definition of the PMF. These approaches attempt to define the “reasonableness” of the manner in which the various flood producing factors are combined by reference to the relative shift in the annual exceedance probability of the event. The implications of the different approaches to deriving the PMF are summarised for a number of dams from across Australia. Guidance on deriving the PMF is provided in the paper with a view to seeking feedback from industry and consideration for inclusion in relevant guidelines.
Paul Somerville, Hong Kie Thio
There is a large degree of uncertainty as to the true state of nature (i.e. epistemic uncertainty) regarding many aspects of seismic hazard analysis. Such differences are often highlighted by differences between alternative models put forth by different model proponents. This epistemic uncertainty is treated by giving weight to all viable alternative models through the use of logic trees in probabilistic seismic hazard analysis, rather than just using a preferred model. This paper reviews epistemic uncertainties that arise from alternative distributed earthquake source models; alternative models for the recurrence of earthquakes on those sources; alternative approaches to including active faults; alternative models for the recurrence of earthquakes on active faults; alternative ground motion prediction models for Australia; and alternative methods for incorporating site response. It also reviews alternative representations of the design response spectrum for the development of ground motion time histories.
2011 – Recent Developments in Seismic Hazard Analysis
Craig Johnson, Mark Arnold
Toorourrong Reservoir is a small storage reservoir which was constructed in 1885 and forms an important part of Melbourne’s water supply network. As part of Melbourne Water’s dam safety upgrade program, remedial works at Toorourrong Reservoir were identified to address deficiencies in flood capacity, embankment stability and to provide protection against piping. These works included an engineered filter system, downstream stabilising berm and raising of the dam crest level by 2.3m through a combination of earthfill and a concrete parapet wall. The existing spillway also required substantial enlargement and the existing scour and outlet structures were to be reconfigured. These works were designed and undertaken by the Water Resources Alliance (WRA).
Preliminary geotechnical investigations indicated the dam was founded on soft alluvial deposits, with the potential for foundation liquefaction under earthquake loading. During the course of subsequent investigations, the full complexity of the dam foundation was realised using numerous techniques including geophysics, CPT
u probes and seismic dilatometer testing. The results of these investigations were used to develop a detailed geotechnical model and embankment design sections. A range of analytical methods were utilised to characterise the liquefaction potential of the foundation, with these making reference to recent developments in this area of practice. Through an extensive assessment and review process, the design soil properties for the foundation were established and the liquefaction potential determined.
Based on these assessments, it was found that the potential for liquefaction existed across the majority of the dam foundation, with discrete soil layers liquefying depending on the intensity of the design seismic event. Strain-weakening (sensitive) soils were also identified in the foundation. A quasi risk-based stability assessment was undertaken for a range of post-liquefaction strength parameters and FoS to determine the sensitivity of the foundation response. Stability analyses were performed which indicated that additional stabilising berms were required at several locations. However, even with these berms, the extremely low post-liquefaction strengths meant that further ground improvement was required. This was assessed further and Grouted Stone Columns (GSC) were ultimately selected as the preferred foundation improvement method for the critical design sections with GSC to be installed both upstream and downstream to reinforce the dam foundation. This is the first time GSC have been used in Australia and some key “lessons learned” will be discussed.
2011 – Toorourrong Reservoir – Small Dam, Big Problems