Steven Rosin and Chen Han Shan
Tailings dam rehabilitation is a major challenge for the mining industry in China requiring a multi-disciplinary approach. A team of Chinese and Australian professionals have recently completed a 4-year project to develop guidelines for rehabilitation procedures for tailings dams in China.
This paper focuses on the geotechnical stability issues that were required to be addressed as part of dam rehabilitation assessment. It also discusses Chinese practices in tailings dam design and operation considered for the assessment. Three case studies are presented from sites in various parts of China.
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David Dole and Brian Haisman
The Murray-Darling Basin Commission recently created River Murray Water, an internal business unit, as a step towards the micro-economic goals of the COAG Water Reforms.
The assets which regulate the River Murray, have a replacement value around $1.4 billion. They range from the 4000 gigalitre Dartmouth Dam in the headwaters, to the 7.5 kilometres of barrages near the Murray mouth and are presently held in trust for the Contracting Governments of the Basin Initiative by one or other of the three riparian states. River Murray Water is bringing the assets together into a single, integrated business with the aim of securing long-run sustainability, funded through pricing for services provided. Broad institutional and pricing principles are described along with the special challenges of an inter-government environment.
These challenges are being met by adopting clarity and simplicity as driving principles, supported by best practice asset information. The paper describes the upfront development of explicit guiding principles and policies, including risk management and dam safety; coordination of activities; generation of life cycle information; and introduction of contestable service provision for the business.
A safety review of the Corin dam has identified several deficiencies including an inadequate spillway capacity. A hydraulic model test, included in the review indicated that the construction of a 1.3m wave wall along the top of the dam was required to prevent overtopping during the flood of 10,000 years.
The original post tensioning anchors installed along the spillway crest were also identified as unreliable due to inadequate corrosion protection measures.
This paper presents safety assessment and aspects of the construction of the remedial works for Corin Dam. As part of the safety review, the condition of the dam was reviewed against the risks of piping, slope instability, flood and seismic forces. The paper also discusses the long term effects of the acidic leakage on the grout curtain and on the integrity of the core.
The risk associated with the flooding during anchor installation and the discovery of a gap formation between the clay core and the concrete spillway wall are also considered.
R J Westmore and P J Cummins
Wartook Reservoir is owned and operated by the Wimmera Mallee Rural Water Authority in western Victoria. The reservoir was constructed in the period 1887 to 1890 on the Mackenzie River within the Grampians National Park. It has a capacity of 29400 ML, is the sole supply of water to the City of Horsham, and also supplies stock, domestic and irrigation water to the Wimmera and Mallee Regions of Victoria.
The embankment is 1100 m long, 12 m high and is constructed of loose to medium density silty fine sands which are susceptible to liquefaction during a seismic event due to the combination of high pore water pressures and low density. Active seepage from the embankment and foundations render the embankment susceptible to failure by piping.
The outlet works were constructed of sandstone masonry and comprise a tower and cut-and- cover conduit buried within the embankment. Inflow of fine sands from the embankment into the masonry tunnel render the embankment susceptible to failure by piping through the joints in the masonry tunnel.
Design concepts for the rehabilitation of the embankment, outlet and spillways have been developed jointly between Wimmera Mallee Water and SMEC Victoria adopting a risk based approach. The design involves partial rehabilitation of the works, providing acceptable levels of risk to the Authority and community, at an economically justifiable cost.
David Watson and John Adem
For several years risk management has been promoted by the Victorian Department of Natural Resources and Environment – Water Agencies as the key mechanism for the effective and efficient business management of dams. As part of an extensive water reform program, the Victorian Government announced in October 1997, a financial assistance package for the water industry which included funding for dam improvements covering a majority of large dam owners in the State. One of the conditions for receipt of these improvement funds was the need for each water authority to undertake a Business Risk Assessment of all significant and high hazard dams under its responsibility.
This paper discusses the Business Risk Assessment document based on a framework developed by Water Agencies after consultation with the industry and expands on the following reasons why the document was produced:
Raymond A. Stewart
On I7 June 1996 while investigating a small pothole on the crest 183 m high Bennett Dam an unexpected crest collapse occurred resulting in a large sinkhole. Following this incident the safety status of the dam was uncertain. The reservoir was lowered by 2 m over a six week period by spilling up to 5,000 m 3 over the spillway and through the turbines.
An unprecedented dam investigation commenced immediately and was completed December 1996. During drilling a second sinkhole was discovered at another location on the dam.
A sophisticated compaction grouting technique was developed to remediate the sinkholes to the depth of 5 m and the work was successfully completed by 1997. -The reservoir was returned to service in time to collect the freshet in spring 1997. This event was the most dam safety concern in the history of BC Hydro operations.
This paper describes how B.C. Hydro managed the crisis, and the subsequent safety assessment.