The SRC operated seismic network is one of the largest privately owned and operated seismic networks in the world. Importantly it bridges the situation awareness gap between the information often provided by national seismic networks, of earthquake magnitude and location, and the emergency response managers questions of “What effects will this event have on my assets?” together with “What should we now be doing to mitigate the event?”
Software development of the Quick Quake app and improved automation of PDF report generation means that detailed, bespoke client specific earthquake response reports that incorporate asset earthquake resistance and failure consequence aspects can be produced by duty seismologists within reduced timeframes.
Preliminary earthquake locations computed by the SRC operated network for the two ML 4.7 Korumburra events in March 2009 and the ML 5.6 Moe earthquake of June 2012 were significantly closer to the final computed locations than those published by any other authority. The network additionally provides bonus outcomes of highly accurate detailed seismic activity maps that reduce uncertainties for Probabilistic Seismic Hazard Assessments (PSHAs) and attenuation data that will be used to develop regional specific ground motion models.
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Thomas Fritz and Peter Lilley
A challenge with managing any diverse portfolio of structures is ensuring that expenditure is targeted at achieving the greatest overall improvement while also safeguarding against individual deficiencies. It is also important to ensure that expenditure is predominantly targeted at achieving outcomes rather than lost in over-exhaustive analysis.
Trustpower is a New Zealand based power generation and multi-retail company. Its dam portfolio contains 47 large dams which spans the whole range from low PIC to high PIC structures with a large variety of different dam types.
In 2014 Trustpower collected all available dam safety information on its large dams in a comparative database. All dam safety relevant structures were split into a number of categories for example stability under EQ loadings. Each category was divided into three sub-categories with a resultant total of 2,739 individual sub-categories which were individually rated based on a rating table with 7 ratings ranging from “desirable” to “deficient”.
All new information as it becomes available is being fed into the database and subsequently individual ratings updated as appropriate.
Annually identified tasks get ranked based on a maturity matrix and the tasks that achieve the highest portfolio wide risk reduction costed and put forward for the following’s year budget for execution.
Jamie Cowan, Chris Kelly and Gavan Hunter
Dam safety upgrade works were undertaken at Tullaroop Dam in 2015/16 to reduce the risk of piping through the main embankment. Unexpected cracking and elevated pore water pressures were observed within this earthfill embankment over a period of 10 to 15 years. In 2005/06 a filter and rockfill buttress local to the embankment was constructed on the left abutment after a 60 mm wide diagonal crack opened up on the downstream shoulder from crest to toe.
Similar to the 2005/06 upgrade works, the 2015/16 embankment works were direct managed by Goulburn-Murray Water. Filter and rockfill materials were sourced from commercial quarries previously used for dam upgrade projects and for which significant testing of materials had been undertaken, especially on the fine filter.
Mid project it became clear that the fine filter was breaking down under handling and compaction such that several in-bank gradings fell outside the specified fine limit. Further testing of quarry surge piles, site stockpiles and in-bank placed filters was undertaken to understand the extent of the breakdown. It was assessed that the breakdown was occurring on the 0.5 to 2.0 mm fraction, generating finer sizes in the 0.1 to 0.6 mm fraction. The increase in fines content (minus 75 micron) was less than 1% and met specification. The in-bank material was accepted as placed and the specified filter envelope adjusted to allow for the observed breakdown.
Difficulties were experienced with compaction of the fine filter in the inclined chimney filter to achieve the target density in the range 65% to 80% Density Index when the layer width reduced to 0.75 m for a 0.5 m compacted lift thickness. No difficulties were experienced when the layer width was 1.5 m or in trenches. Further trials were undertaken on the embankment to better understand the compaction issues and used different roller types. It was assessed that an important factor was the arching effect of the adjacent coarse filter. Going forward thinner lifts were used and smaller width rollers to achieve the specified minimum density.
The paper provides details on the embankment construction works, focusing on the fine filter breakdown and compaction issues. Details of the testing undertaken, the actions to resolve the issues and interactions with the supply quarry and construction team are provided.
Peter Buchanan, Malcolm Barker, Paul Maisano, Marius Jonker
Kangaroo Creek Dam located on the Torrens River, approximately 22 km north east of Adelaide, is currently undergoing a major upgrade to address a number of deficiencies, including increasing flood capacity and reducing its vulnerability to major seismic loading.
Originally constructed in the 1960s and raised in 1983, recent reviews have indicated that the dam does not meet modern standards for an extreme consequence category dam.
The original dam was generally constructed from the rock won from the spillway excavation. This rock was quite variable in quality and strength and contained significant portions of low strength schist, which broke down when compacted by the rollers. The nature of this material in places is very fine with characteristics more akin to soil than rock. Review of this material suggests that large seepage flows (say following a major seismic event and rupture of the upstream face slab) could lead to extensive migration of the finer material and possible failure of the embankment. However, it is also envisaged that the zones of coarser material could behave as a rockfill and therefore transmit large seepage flows, which may result in unravelling of the downstream face leading to instability.
This paper addresses the design of the embankment raising and stabilising providing suitable protection against both these possible failure scenarios, which tend to lead to competing solutions. The final solution required the embankment to be considered both as a CFRD and a zoned earth and rockfill embankment.
Amanda Ament, Thomas Ewing, Frank Nitzsche
The automatic operating buoyancy type spillway gates at Lenthall Dam did not operate properly since installation. This paper discusses the problems encountered, the investigation conducted using computational fluid dynamics to quantify the problems and develop solutions. It describes the design of the modifications to the gate and flow regime and results after construction.
Robert Shelton, Jako Abrie, Matt Wansbone
The Mahinerangi dam – arguably the most valuable in Trustpower’s portfolio of 47 large dams – is over 80 years old and needs a plan of work to confirm it meets current design standards.
The dam was completed in 1931, subsequently raised in 1944-1946, and strengthened with steel tendon anchors in 1961.
A comprehensive safety review (CSR) in 2007 noted a potential deficiency in the fully grouted anchors and a program of work commenced to re-evaluate the overall stability of the dam.
A potential failure mode assessment revealed that the dam may need upgrading to meet the criteria for maximum design earthquake (MDE). Areas of uncertainty were identified and a significant programme of survey, geological mapping, concrete testing and site specific seismic assessments have been carried out to reduce risk and uncertainty in design.
The paper discusses the dam’s history, current condition, and describes the ongoing programme of work planned to extend the life of the dam for another 80+ years.