I A Howley, G S Smith and D J A Stewart
Over the past decade the role of dam ownership in Victoria, and indeed Australia, has changed from one of owners, constructors and operators of large civil assets, to managers of structures on behalf of owners of the entitlements to water. This is part of the key business focus to dams management in Victoria.
This position has been heavily influenced by regional water reform policies, such as the Murray Darling Cap, and its effects in Northern Victoria, and COAG Agreements.
Dam owners now run service driven businesses, with a clear separation of roles and responsibilities from the traditional, engineering focused organisations which were established in an environment of resource development. The environment is now one of maintenance, service delivery, structure maintenance and long term business viability for ultimate community benefit.
By using Goulburn-Murray Water as an example, the current model of dams management in Victoria is outlined, together with possible future directions for the rural water industry in Victoria.
Brian A Forbes and Jon T Williams
The 43 metre high Cadiangullong Dam was constructed during 1997-1998 to supply untreated water for the Newcrest Cadia gold mine near Orange in NSW. The placement of the 110,000 m3 of RCC was performed without expensive thermal control techniques in an area of extreme climate conditions. Thermal finite element studies were undertaken during design to assess the effect of the climate extremes on construction and assist in the design of contraction joints. An RCC mix with sand proportions in excess of 50% of the fully crushed aggregate by weight was used to eliminate segregation. This also had the effect of requiring a low compaction effort to achieve density but exhibited a sheared surface texture if placed over wet. Following full scale trials the conventional concrete facing was superseded during the early stages of construction with an in situ modified RCC facing. The modified RCC consisted of a grout enriched internally vibrated RCC (GE-RCC) to provide a durable, impervious upstream face. This paper discusses the details of these three aspects and provides design, construction and performance data to date.
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.
Andrew Pattle and Bram Knoop
This paper provides an outline of a process that can be used to optimise regular dam surveillance and monitoring activities. The process is applicable for a wide range of dam types that an owner/operator may be responsible for. Basic assessments are made of inherent reliability and potential consequences of failure using key factors such as construction features, foundation conditions and observed performance. The key factors are combined to give a relative risk ranking for each dam. These rankings are used to determine specific dam monitoring schedules. The process focuses the monitoring effort on those dams that are perceived to constitute the greatest portion of the overall risk. The methodology is simple and provides a cost-effective framework for setting appropriate resourcing levels for dam monitoring.
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:
D. B. Edwards, B.H. Jackson & R. H. Wright
Ground anchorages are installed to support structures such as dams, slopes and tunnels. Failure of anchorages could be serious.
The condition of these critical supports is currently assessed by monitoring the load in the anchorages by either load cells or lift-off testing (jacking). Both methods are expensive and testing may damage the corrosion protection beneath the anchorage head.
A non-destructive testing method for ground anchorages needed developing and the UK Universities of Aberdeen and Bradford developed a testing system called GRANIT with patent applications on the system filed world-wide.
Full scale measurements were conducted during the construction of Penmaenbach and Pen y Clip Tunnels on the UK’s A55, where rock support was provided by prestressed rock anchorages. In all 9000 records of anchorage response were analysed.
A major finding from the research was that the response of the anchorages to the dynamic impulse motion produced by the blast loading depended on how the anchorage had been constructed and on the nature of the surrounding rock mass. If the prestress load in the anchorage was changed, or the free length increased, a noticeable change was observed in the response ‘signature’ as monitored by an accelerometer located at the anchorage head.
Applying a known impulse load to the anchorage head immediately after construction and measuring the response, provides a datum response signature for the intact anchorage. If the anchorage was to deteriorate in any way, eg loss of prestress, this should be noticeable on subsequent response signatures. This approach is the basis of the GRANIT system.
A short programme of anchor calibration testing for bolts was conducted in Hawkesbury sandstone in Sydney during March 1998 and developments in Australia and UK are proceeding.