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Papers

Papers are made available through the website 12 months after they are presented at the annual conference. Please add to your shopping cart to purchase and you will receive a link to download.

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A CD can be purchased containing ANCOLD Bulletins from 1961 to 2001 on the OTHER PUBLICATIONS page.

If there is a paper you require prior to 2007 that has not been uploaded please contact the secretariat [email protected]

Use the search below using keywords, year or author.

$15.00

1998 Papers

1998 – Safety of Meadowbank Dam Against Sliding Parameter Uncertainty
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Richard I Herweynen

For concrete gravity dams, when the foundation’s value of cohesion is low, it is very difficult to meet the sliding criteria proposed by ANCOLD. Low cohesion is generally associated with serious foundation defects. This was the case for Meadowbank Dam, with a foundation having persistent horizontal seams containing material of a clayey silt size classification. By adopting the ANCOLD strength reduction factors, it was found that a large number of ground anchors would be required to meet the ANCOLD sliding criteria. During original design, extensive laboratory and insitu testing was performed on the seam material. This paper proposes a methodology for arriving at less severe strength reduction factors based upon a statistical analysis of the strength parameters measured in the Meadowbank Dam foundation.

Additionally, a probabilistic approach using a Monte Carlo simulation is used to give further weight to this argument. This paper concludes that the probability of Meadowbank Dam failing due to sliding is very low and within acceptable limits.
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1998 Papers

1998 – “PREP” – A Lower Risk Approach to Dam Safety Prioritisation
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D.N.D. Hartford and R.A. Stewart

It seems perfectly logical, obviously desirable and apparently sensible to prioritise dam safety reviews, deficiency investigations and capitalised remediation projects in terms of risk. However, our experience in attempting to apply the various deterministic and risk- based approaches in prioritising dam safety activities has revealed that, while it may appear to be quite logical and desirable to prioritise in terms of risk, it is rather less feasible than it appears.

This paper explores why different prioritisation processes can lead to different priority rankings across the same portfolio of dams. B.C. Hydro’s Preliminary Risk Exposure Profile process, which utilises the best and most robust attributes of risk analysis process at the preliminary level but avoids the pitfalls associated with estimating risks which will often have little or even no basis is presented. The paper explains how this process provides a “fail-safe” backup which will identify non-conservative and erroneous facility risk estimates; thereby allowing for correction in a timely fashion. The paper also raises some awkward philosophical issues which the profession will have to address in order to permit confident dam safety decision-making on the basis of risk analyses. Not the least of these is the following issue – “If preliminary estimates of risk are reasonably good, then there should be little need for more detailed risk analysis for confident and defensible decisions concerning making or not making dam safety improvements”.
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1998 Papers

1998 – Estimating the Probability of Failure of Concrete and Masonry Gravity Dams
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Kurt Douglas, Matt Spannagle and Robin Fell

This paper describes a method for estimating the probability of failure of concrete and masonry gravity dams through the dam or the foundation. The method is based on the research and analysis of historic failures and accidents performed at The University of New South Wales over the last two years. The method accounts for dam type; age; foundation; height/width ratio; dam performance observations; and monitoring and surveillance.
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1998 Papers

1998 – Risk Assessment – Estimating the Probability of Failure Embankment Dams by Piping
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Mark Foster, Robin Fell and Matt Spannagle

This paper describes a method for estimating the probability of failure of embankment dams by piping. The so called “UNSW method” is based on the results of an analysis of historic failures and accidents of embankment dams. An estimate of the probability of failure of a dam by piping is made by adjusting the historical rates of failure by piping by applying weighting factors which take into account the dam zoning; filters; age of the dam; core soil types; compaction; foundation geology; dam performance; and monitoring and surveillance. The method is intended for preliminary assessments only and is ideally suited as a risk ranking method for portfolio type risk assessments to identify which dams to prioritise for more detailed studies and as a check on event tree methods.
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1998 Papers

1998 – Portfolio Risk Assessment of SA Water’s Large Dams
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David S. Bowles, Andrew M. Parsons, Loren R. Anderson and Terry F. Glover

This paper summarises the Portfolio Risk Assessment (PRA) process that was implemented for SA Water’s 17 large dams, the information obtained from the PRA, and its use by SA Water. The PRA was designed to provide a baseline assessment of the existing dams and an initial prioritisation of future investigations and possible risk reduction measures. The PRA comprised a reconnaissance-level engineering assessment and risk assessment. These assessments were performed for floods, earthquakes, and static loading. Various structural and non-structural risk reduction measures were developed and evaluated. Information from the PRA can be used to provide inputs to capital budgeting, due diligence and liability evaluations, contingency planning and business criticality assessment, evaluation of loss financing and insurance programs, and a firm basis for monitoring and surveillance, operations and maintenance, and emergency preparedness planning.
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1998 Papers

1998 – Risk Assessment for Hume Dam – Lessons from Estimating the Chance of Failure
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Leonard A McDonald and Chi Fai Wan

A risk assessment has been undertaken as part of a comprehensive review of the safety of Hume Dam. Use of risk assessment techniques, to assist in evaluating the safety of existing dams, is a relatively recent trend. Hume Dam was a particularly challenging subject for the application of risk assessment techniques at their present stage of development. The challenge lay in the number and diversity of dam elements to be analysed, in the number and complexity of the potential failure modes and in the fact that there were significant safety issues under normal operating conditions.

This paper outlines some of the key lessons learned from that phase of the risk assessment that was concerned with estimating the chance of dam failure. Some of the issues discussed have not previously been addressed in the literature and some demonstrate a clear need for improved analysis procedures.
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1998 Papers

1998 – Risk Based Approach to Wartook Reservoir Rehabilitation
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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.
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1998 Papers

1998 – WAC Bennett Dam – The Sinkhole Crisis
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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.
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1998 Papers

1998 – Geotechnical Assessment and Rehabilitation Challenges for Tailings Dams in China
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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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1998 Papers

1998 – Matahima Dam Strengthening Project Management Design, Consents and Construction
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Steve Everitt, Ron Fleming, Lelio Mejia

The Electricity Corporation of New Zealand Ltd (ECNZ) is strengthening its Matahina Dam which is an 80 m high, 400 m long rockfill dam impounding a 60 million cubic metre reservoir. The strengthening is to ensure the dam will withstand potential fault displacement within the dam foundation.

ECNZ’s management of the project is described from the design and consents phase through to construction. Key issues are discussed which have contributed to the success of the project such as management structure, the International Review Board, the design process and risk management.
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1998 Papers

1998 – Repair of Two Dams Suffering Leakage – Two Case Studies
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Nikifor Petrovic

One of the most important issues during design and construction of an earthfill dam is how to secure a dam against unwanted events which may occur as a result of water flow (uncontrolled seepage, leakage & piping) through the dam.

Although earthfill dams are the largest by volume compared with other types of dams and they are designed to cope with seepage, their integrity is most sensitive to the effects which may be caused by it. The reason being that the earthfill materials are generally extremely heterogeneous and only one “unwanted” pocket is enough to create problems.

Another critical area is the foundation. In many situations it is not possible to avoid the complex geology which includes faults and joints as part of the foundation. An additional complication may be the presence of dispersive clay in the foundation.

In the area of tailings dams, the problems with seepage are slightly reduced as in most cases, tailings provide a degree of sealing. Tailings dams are very often designed as leaky dams. However, there is a hidden danger in approaching the design this way as at any stage of their lives they can retain water.

This paper presents two case histories of repairs carried out to tailings dams suffering leakage. One case describes leakage through the embankment wall while the other describes seepage through the foundation which contains dispersive soil.
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1998 Papers

1998 – Heritage Planning for Dams
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Tony Moulds

A dam owner is often surprised to learn that his dam has been listed on a heritage register. This is often the first indication that the dam has heritage significance.

This paper discusses the different types of heritage listing and what the implications are for an owner. It suggests that a prudent owner will find out whether he needs a heritage conservation plan, particularly where redevelopment or remedial work at the dam is contemplated. The paper describes the content of a typical conservation plan for a large dam and how it is implemented.
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