There are many international guidelines, state regulations and technical standards relating to tailings disposal. In addition, the larger mining companies have their own in-house standards and design rules with competent personnel in charge of their operations. Sound embankment design methods can be used by most designers familiar with earth dam design.
The paper gives a listing of many of the current sources of information and guidance available, with some comments by the author on their perceived relevance to the Australian mining industry. Despite the availability of a number of other guidelines at the time, the need for Australian Guidelines was recognised in the mid 1990s and the reasons for the development of the 1999 ANCOLD Tailings Guideline are explained.
Perhaps the best recognition of the need for the original ANCOLD guideline is the degree to which it has been adopted since publishing the 1999 edition. It is in almost universal use in the Australian mining industry and is recognised as providing appropriate and acceptable standards by all state governments. Its use is recognised and sometimes even specified by a number of neighbouring countries and it is also recognised internationally when used by Australian companies with overseas operations.
The reasons for this wide acceptance are described. However, there are some areas where more recent developments have led to the Guidelines becoming dated and improved international guidelines have been published since 1999. The need for a revised ANCOLD guideline and its elevance is then described.
Keywords: Tailings, dams, mining, guidelines
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Gavan Hunter and James Toose
Hinze Dam, an extreme hazard storage, is under the authority of Seqwater (Southeast Queensland) and is the principal potable water storage supplying the Gold Coast. The Stage 3 raise, presently under construction, involves raising the embankment almost 15m to a maximum height of 80m.
The central core earth and rockfill embankment is founded on competent greywacke rock within the valley floor and left abutment. On the right abutment it is founded on extremely weathered greywacke and rockfill stability berms were constructed upstream and downstream on this weak foundation.
Key issues for the design of Stage 3 embankment raise on the right abutment were: 1/ removal of the existing downstream stability berm and deep excavation at the toe of the Stage 2 embankment to connect into the blanket filters under the downstream shoulder; 2/ the soil strength properties of the weathered greywacke foundation and the presence of pre-sheared defects with strength properties significantly below the strength of the soil mass; and 3/ undertaking the works while the reservoir remained in operation and close to full supply level.
It was not possible to undertake large scale excavation at the downstream toe of the right abutment as the factor of safety for the excavation condition was below the design criterion for slip surfaces extending back to the upstream shoulder. The innovative design solution was for a staged excavation and back fill operation up the right abutment. In this ay the stability requirements were achieved by a 3-dimensional buttressing support and reduced the time that critical excavation sections were exposed.
The construction risk is being managed under a dam safety management plan. Key elements of this plan include instrumentation monitoring and increased surveillance for early detection of a potential incident, a series of trigger levels and responses to these levels, a clear hierarchy of contacts and adequate preparation for a dam safety emergency (including materials, personnel and equipment).
The embankment construction is presently in progress. The most critical sections have been successfully completed without incident and displacements are within the predicted range. Communication and planning within the Alliance between the designers and constructors has been a key element in the successful construction works to date.
Keywords: construction risk, embankment design, embankment construction, dam safety management
M. Amghar, A. Watt, C. Thorstensen
The future effects of climate change on water resources in the 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. In Southeast Queensland, concern for climate change has increased in recent years with research on global climate change applied to part of Southeast Queensland and it has become apparent that the region’s climate has changed in recent times. Studies have shown that Southeast Queensland’s climate has been variable over history and in the present, is experiencing continuing sea level rise, and may experience
significant climate warming. The potential effects of climate change on coastal erosion, water availability, flood control, and general water management issues have been raised and widely discussed from a variety of perspectives.
This paper presents results of an integrated economic-engineering resource assessment optimisation model of Seqwater’s water supply system illustrating the value of optimisation modelling for providing an integrated approach needed to manage a complex multipurpose water system. Overall, the approach has its own limitations, but provides useful insights on the potential for operating the current or proposed infrastructure for different future conditions.
Keywords: Brisbane Water supply, Moreton, water resource plan, optimisation, environmental flows.
Australia’s prosperity is closely linked to the development of mining. Tailings production has always been associated with mining and acceptable management strategies of tailings have progressively developed to meet ever changing community expectations. In the late 1800’s, tailings were typically dumped into streams or onto land as mullock heaps, resulting in severe pollution. Practices gradually changed so that by the 1920’s tailings were often held in dams or ponds. However failures were common with slugs of slimes and contaminants moving down watercourses. For the purpose of protecting life and property, States started regulation of the management of tailings under various dam safety umbrellas in the late 1980’s. In 1995, Queensland, in consultation with stakeholders, produced tailings management guidelines, which enunciated good tailings management principles. Later guidelines have incorporated many of these principles. In 2002, the regulation of tailings disposal in Queensland moved into the Environment and Resource Management framework, where the emphasis is on obtaining a sustainable environment. Emerging practices are seeking better ways of incorporating mine tailings into the environment with minimal impact. Backfilling of mine workings, integration of mine waste facilities and beneficial use are some of the methods now used for tailings disposal. This paper looks at the historical management of tailings, the evolving regulatory framework, and the emerging practices for protecting the environment while allowing for development that improves the total quality of life, both now and in the future, in a way that maintains the ecological processes on which life depends.
Keywords: Dams, Tailings, TSF, Community, River Pollution, Cleanup, Risk, Mining
Peter Cordi, Paul Fuller
Tallowa Dam was completed in 1977 at the junction of the Shoalhaven and Kangaroo Rivers in the southern highlands of NSW to provide a pumping pool for water supply transfers to Sydney. These transfers were made only during drought periods, at which time limited and fixed environmental flow releases from a low level outlet were made to the downstream Shoalhaven River. After extensive consultation with the local community the Government decided in 2006 to commence transfers earlier in the drought cycle, and release variable amounts of surface water to improve river health during transfer periods. In addition, Tallowa Dam was identified as having a significant impact on fish passage, as many species migrate to the estuary during their life cycle, and approximately 75% of the viable fish habitat was upstream of the dam. This project involved the design and construction of works to be retrofitted to the dam to address both issues. A surface water release slide gate in the spillway, a low friction coating on the spillway, and a downstream weir were constructed to release environmental flows and allow safe downstream fish passage. A new fish attraction flow outlet was drilled through the dam wall, and a fish attraction chamber and a travelling bucket fish lift was installed for upstream fish passage.
Keywords: environmental flows, fish passage, Shoalhaven River, construction.
Alice Lecocq, David Brett, Mike Rankin
Tailings Dams class amongst the world’s largest man made structures. They are interactive structures that evolve over time, with tailings discharge, water management, embankment raising and finally closure and abandonment. Understanding of the design, the impact of operations and regular, committed surveillance is essential to ensure the safety and performance of a tailings dam. Dam Safety Management Plans should be developed to optimise these parameters. These plans should include Operation, Maintenance and Surveillance (OMS) manuals, emergency response plans and monitoring databases. They should be managed by the mine management and implemented by the operations personnel.
The tailings dam operators are the key to a successful dam safety management program. It is imperative that the tailings dam management and operators appreciate the risks inherent with the facility, their role and their responsibilities. They also need to have an appropriate understanding of the tailings dam design features, failure modes and safety triggers. With training it is expected that personnel will be better able to recognise and act on safety issues arising.
The paper presents case histories of tailings dam failures due to poor operation and management and outlines the operational requirements and risks inherent with tailings dams. The paper discusses the training approach and criteria to be adopted, and describes a training course developed by the authors for mine management and operators. The paper examines the feedback collected from the courses held at several mines. A model to successfully implement a surveillance program with the involvement and leadership of the operators is proposed.
Keywords: TSF failures, surveillance program, OMS manuals, training of personnel.