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.
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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 Following full scale trials the conventional concrete facing was superseded during the early stages of construction with an in situ modified RCC facing.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.
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.
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.
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.
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.