Bob Wark, Paul Hurst, Andy Peek
Current practice has been to use API Spec 10 Class G oilwell cement for the bond zone of post-tensioned ground anchors for dams. Historically, the concern had been that the use of AS 3972 Type GP cement and AS 1478 Type HWR water reducers (“superplasticisers”) would have adverse effects on the corrosion resistance of bare strand in the bond zone, due to additives present in some types of superplasticiser.
The superior fluidity of grouts using Type GP cement, together with the cement availability and potential economy, lead the authors to run accelerated corrosion tests based on the ASTM B117 Neutral Salt Spray Test, using sections of tendon embedded in a grout of Type GP cement and a modern superplasticiser alongside similar samples using Class G cement.
This paper describes the results from the testing, which indicate identical corrosion protection performance from both types of grout over a total of 5,000 hours exposure.
Keywords: Post-tensioned anchors, oilwell cement, superplasticisers, Type GP cement, corrosion protection
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Rob Ayre, Simone Gillespie, Peter Richardson, Mark Harvey
In November 2007, NQWater (now Townsville City Council) completed the upgrade of Ross River Dam near Townsville. This upgrade included the installation of a Program Logic Control (PLC) operated radial gate structure in the existing spillway. The purpose of the upgrade was threefold; to meet current design standards regarding dam safety and flood capacity; increase the town water supply to Townsville and Thuringowa; and to maintain the flood mitigation benefit of the dam during flood events in the Ross River catchment.
The designers of the dam upgrade completed a risk assessment at the commencement of the design phase and concluded that a PLC operated gated dam posed less risk than an approach that relied purely on dam operators. This is seen as the “new way forward” in gate operated dams by many designers. The regulator of dam safety in Queensland has indicated a preference for an operator to remain on site full time whilst the PLC system is ‘proved’. As a consequence a flood operations team was engaged to monitor the dam during times of flood through the commissioning period of the upgrade.
This paper discusses the lessons learnt from the experiences of the Ross River Dam during its first few flood events and issues associated with the adopted design approach.
Keywords: Dam Safety, Gated Spillway, Flood Operations, Ross River Dam, NQWater, Townsville City Council, SunWater, Queensland.
Russell Paton, Peter MacTaggart, Lee Benson
The Nathan Dam project has been identified by the State Government of Queensland as a potential water supply option to facilitate future growth in central Queensland. The proposed storage is located approximately 69 km downstream of the township of Taroom and would have a storage capacity of 1,080,000 ML which would make it Queensland’s fourth largest storage.
The proposed dam arrangement includes a central concrete gated spillway section across the river in order to maximise the storage volume and limit the flood rise upstream such that flood levels at Taroom are not increased during major flood events. A high level fixed crest spillway, to assist in the passage of rare flood events, forms the right abutment portion of the dam wall. It is proposed that the bulk of the concrete sections of the dam be constructed using roller compacted concrete (RCC).
The investigations to progress Nathan Dam are complicated by the existence of the Boggomoss Snail (Adclarkia dawsonensis) within the proposed inundation area. The snail is listed as a critically endangered species under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act), and a proportion of the snail’s known population is located on a Boggomoss (the colloquial name for an artesian spring) that will be inundated should the project proceed.
SunWater has engaged Australia’s foremost expert on land snails to design a translocation process aimed at relocating the species to alternative habitat outside the inundation area. The process will seek to not only protect the snail from the dam development, but to increase both its numbers and distribution thereby reducing risks to the currently isolated population from threats such as fire and predation. It is the first time in Australia that such a trial has been attempted, and SunWater is working closely with the Federal Department of Environment, Water, Heritage and the Arts (DEWHA) to ensure that the process is consistent with their policies and guidelines.
The paper will discuss the engineering and environmental challenges of the dam and how the Environmental Impact Study process can influence the delivery of a project.
Keywords: Nathan Dam, Environment, Engineering
Martina Reichstetter and Dr Mohand Amghar
The future effects of climate change on water resources in southeast Queensland and other parts of Australia will depend on trends in both climatic and non-climatic factors. Evaluating these impacts is challenging because water availability, quality and streamflow are sensitive to changes in temperature and precipitation. Other important factors include increased demand for water caused by population growth, changes in the economy, development of new technologies, changes in catchment characteristics and water management decisions.
This paper provides an overview of how climate change may affect water yields and water availability in the Tinana Creek catchment. The Tinana Creek water supply is located in the south-eastern costal area of Queensland and covers an area of 783 km2. The catchment experiences a sub-tropical climate with warm to hot summers and mild dry winters. Climate variation and change are expected to impact the upper Tinana Creek water supplies and the planning of potential future water supply options. The Maryborough City’s water supply is currently supplied solely by Teddington Weir to domestic and industrial users. In this paper, climate change impacts on the water yields were investigated by assigning climate change, derived from SimCLIM, onto the input data used in the Sacramento rainfall-runoff model and Integrated Quantity and Quality Model (IQQM). Eighteen different climate change scenarios were undertaken, using three different Global Climate Models (GCM) (CSIRO MK2, HadCM3 and CGCM2), three different emission scenarios (A1FI, B2 and A1B) at two different time steps (2030 and 2050). This paper presents results with current and future climate scenarios of water availability in the study area.
Keywords: Teddington Water supply, IQQM, water resource plan, climate change, SimCLIM, Maryborough.
David Brett, Bruce Brown, Imran Gillani, David Williams
This paper reports the direction of a current review of the 1999 ANCOLD Guidelines on Design, Construction and Operation of Tailings Dams. A sub-committee has been formed and has determined that the majority of the current guidelines need only minor editing but that additional attention is required to the concepts of risk and design for closure.
Major mining companies recognise that effective operation and closure of their tailings facilities are fundamental to their continued business from financial and political aspects. Risk needs to be managed throughout the life cycle of a TSF through planning, design, operation, closure and post-closure. Various methods are used to assess the “consequence category” of a TSF. This then determines design and operational criteria. Risks are identified and controls developed to limit these to acceptable levels.
The involvement in the sub-committee of representatives of the mining industry gives an industry perspective to this issue. This includes determination of acceptable risk levels and how to manage operations to achieve them.
The current ANCOLD Guidelines are very limited in terms of guidance for closure and possible abandonment of TSFs. However this area is perhaps the most critical from an economic and environmental perspective. The issues to be faced at closure and post-closure should be considered at the planning and design phases. The paper outlines some of the post closure cases that might need to be considered in design.
Keywords: guidelines, tailings dams, ANCOLD
Many earthen dams and embankments throughout the world are in need of remediation to address seepage or other issues and ensure structural integrity. Borehole drilling plays a vital role in facilitating implementation of remedial designs, both in the initial information gathering stage and the actual construction of a chosen remedy.
Within the past six to eight years Sonic drilling has become recognized within the geotechnical community as a viable method to meet overall project objectives and address site specific issues for a variety of projects. Key aspects of Sonics include: the ability to efficiently penetrate difficult subsurface conditions, provide a continuous core sample of unmatched quality, and minimize or eliminate risk to the structure from the drilling process. This paper focuses on the application of Sonic in support of a remedial effort at Wolf Creek Dam, including information on the background and overall objectives of the project, a brief explanation of the Sonic method, the scope of services required at the site, and the specific reasons for utilizing Sonic in this case.
Keywords: sonic drilling, grout curtain, Wolf Creek Dam, dam remediation