David Reid, Andy Fourie, Riccardo Fanni, Cristina Vulpe, Alexandra Halliday
Recent failures of a number of tailings storage facilities (TSFs) has highlighted the need for better
governance and operational management of these structures. One means to improve their safety is clearly better and more focussed monitoring. Significant efforts are underway in this area, with a number of technologies being deployed. In particular, the monitoring of deformations through a variety of means (direct, satellite inferred) is increasingly being applied. While deformation monitoring to warn against failure has a long history in geotechnical engineering, some aspects of the rapid triggering and resulting flow of some TSFs may not be amenable to deformation monitoring, in the sense that actionable warning of an impending failure is not assured.
To examine this issue, a series of numerical models of an idealised TSF are carried out. This idealised TSF is brought to failure by means of a rising phreatic surface – often referred to as the constant shear drained (CSD) stress path. Deformations of the outer slope and crest of the numerical model – i.e. those that could be monitored for a real TSF – are tracked and analyses for the models carried out. It is seen that under CSD loading distinct deformation patterns indicative of impending failure are not always clear. Rather, minimal deformations and indeed swelling of the crest is seen leading to failure. The importance of recognising the minimal pre-failure deformation patterns that may manifest with a rising phreatic surface is noted.
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Now showing 1-12 of 37 3483:
David Stephens, Phillip Jordan, Peter Hill, Tim Craig, James Woolley and Bill Hakin
As part of the design of a proposed new hydropower dam (the Alimit HPP), on the island of Luzon in the Philippines, design flood estimates have been prepared using a RORB Monte Carlo approach for events up to and including the Probable Maximum Flood. Compared with Australia, the Philippines is a relatively data sparse environment, with limited rainfall gauge records and even fewer streamflow gauging stations. As such, considerable effort was required to derive design rainfall inputs for Monte Carlo simulation, including rainfall depths as well as temporal and spatial patterns.
This project made use of a number of remotely sensed data sets, including 20 years of global half hourly gridded rainfall data from NASA and global gridded estimates of rainfall intensity-frequency-duration. As part of the project, these data sets were benchmarked against local records from Luzon as well as selected Australian data sets.
This paper sets out the process used to determine design flood estimates in the Philippines, as well as summarising the usefulness of these new data sets for potential application in data sparse regions of Australia.
Richard M Robinson, Siraj Perera, Gaye Francis
SFAIRP (so far as is reasonably practicable) is the ‘modern’ definition of ‘safe’. Shrouded in the legal
concept of the ‘safety case’, it is actually the judicial form of the principle of reciprocity – the golden rule – do unto others, incorporated into the common law by the Brisbane born English law lord, Lord Atkin in 1932.
In dam safety terms, it asks the question; “If you lived downstream of a dam, how would you expect the dam to be designed, operated and maintained in order for it to be considered safe?”
The answer is that it now requires a public demonstration that all reasonably practicable precautions are in place in a way that satisfies the will of our parliaments and our sovereign’s courts, otherwise known as a SFAIRP safety case.
Christopher Dann, Chad Martin, Garry Fyfe, Nigel Rutherford
This paper presents a case study on remedial works that were undertaken at Lock and Weir One
along the River Murray, that to our knowledge are the first of their kind in Australia.
The weir structure’s left abutment is comprised of a stepped concrete structure founded on timber
piles, with timber sheet piles extending beneath the structure to cut off seepage through underlying
alluvium. A piping incident occurred at the left abutment in late 2014 and a filter blanket was
installed as an emergency response measure. A detailed review of historic construction documents
showed that there was a “missing” timber sheet pile upstream of the piping boil. Geotechnical
investigations, including piezometer installation confirmed the missing timber sheet pile was the
likely cause of the piping incident. A piping risk assessment showed the residual risk of further piping
was reasonably high.
A range of remedial works was considered as permanent risk reduction works. However, these
solutions required extensive temporary works to expose the missing timber sheet pile including a
cofferdam to access the defect and partial demolition of a recently constructed fishway structure.
An alternate Secant ‘Grout Column’ solution was developed that comprised targeted drilling and
backfill grouting to close the gap where the sheet pile was not installed and to grout an inferred void
under the abutment structure. This solution was successful at reducing seepage through the
abutment structure, as indicated by monitoring piezometers.
Zara Bostock, Helena Sutherland
Ewen Maddock Dam is located approximately 12.0 km west of Caloundra, in the Sunshine Coast area of Southern Queensland. The dam is a homogeneous earthfill embankment dam 10.5 m high and 724 m long. The dam was originally built between 1973 and 1976 and later upgraded in 1982 to raise the ogee spillway crest by 2.44 m to the current Full Supply Level (FSL) of 25.38 m AHD.
Seqwater is undertaking a staged upgrade of Ewen Maddock Dam to address deficiencies identified during the Acceptable Flood Capacity (AFC) Review (GHD, 2010). The consequence category assigned to Ewen Maddock Dam is ‘Extreme’ with a downstream Population at Risk greater than 1000.
Stage 1 construction was completed in 2012 to manage the seepage underneath the dam to reduce the risk of piping and improve embankment stability. Stage 2A involved retrofitting a filter in the existing embankment and raising the dam 1.61 m to 30.11 m AHD using a reinforced concrete parapet wall. Stage 2B involves spillway upgrade works and was split from 2A due to approval constraints.
Stage 2A construction was completed in April 2021, navigating various project and dam safety challenges. This paper presents some practical ways dam safety and risk was managed on the ground from the perspective of both the designer and owner.
Chris Nielsen, Ron Guppy, Gary Hargraves, Robert Fowden
Dam safety upgrade projects of major dams typically involve a large capital investment. It is important that expenditure decisions are based on sound criteria, both technical and non-technical. Independent peer review of technical matters plays a key role in meeting design, construction and safety objectives within practical financial constraints and assuring robust, resilient and reliable project outcomes.
An independent technical review is recommended for all dam projects.
The Queensland dam safety regulator has developed guidelines associated with technical review for dam safety projects that considers scope and limitations, expertise and governance. The guidelines are informed by literature, recent projects, a commission of inquiry, internal and external review and industry feedback. The guidelines are being implemented across major dam safety upgrade business cases through preparation of terms of reference by the Queensland Government’s business planning and implementation entities, who maintain the responsibility of providing assurance to state government projects, as well as the state’s major dam owners.
The terms of reference, supported by the underlying principles in the guidelines, provide a platform for consistent and appropriate application of technical assurance to dam projects in Queensland. Among other matters, governance is highlighted as a critical factor for success as well as clarity of the roles, responsibilities and reporting lines of all parties. The application of both guidelines and terms of reference to recent projects is discussed.