David Piccolo, Gareth Swarbrick, Garry Mostyn, Bruce Hutchison, Rodd Brinkmann
Hillgrove Resources owns and operates Kanmantoo copper mine some 44 km southeast of Adelaide.
An important feature of the mine is its tailings storage facility (TSF) which is fully lined with HDPE, and double lined at the base, fully under drained, has a secondary underdrainage system for leak detection and a multi-staged centralised decant system. This onerous design of the TSF was developed in consultation with DMITRE between 2007 and 2010 amid concerns of groundwater protection and effective water management.
The Authors were approached in 2010, following construction of the initial stage of the TSF, and charged with developing the design to increase storage from 13 to 20 million tonnes, as well as optimising the design and construction of future stages.
This paper presents the more interesting aspects of the design and construction optimisation between 2010 and 2016 including:
The design and construction approaches have been scrutinised and accepted by regulatory authorities, and implemented by the mine operator over a period of 6 years. The paper includes lessons learnt during the implementation process.
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Shane McGrath, Stuart Richardson, Mark Arnold
Melbourne Water Corporation has recently completed a complex safety upgrade of Greenvale, an extreme consequence category dam. An assessment concluded that the residual risks were As Low as Reasonably Practicable (ALARP). However, given the uncertainty associated with the calculations the estimated residual societal risk was not comfortably below the limit of tolerability. Melbourne Water has experience with preparing hazardous industry safety cases for its water treatment chemical storages and decided to trial the methodology for Greenvale Dam. This paper describes the approach taken in hazardous industries to construct safety cases and how his was adapted to demonstrate that dam safety risks are ALARP.
K.A. Crawford-Flett, J.J.M. Haskell
Dam inventories can provide a comprehensive understanding of a region’s dam population; from dam quantity, type, age, height, and purpose; to ownership profiling and broad-based regional risk assessment using GIS applications. Historically, New Zealand has lacked a comprehensive inventory of dam assets, instead relying on local and industry knowledge to characterise the dam infrastructure and its key properties, issues, and risks.
This paper presents a cross-sectional characterisation of dams in New Zealand, based on the recent compilation and analysis of a New Zealand Inventory of Dams (NZID). The NZID is the first inventory of its kind for NZ dams, comprising almost 1200 unique structures over 3 m in height. Inventory data was sourced from existing publications, NZSOLD, and regional authorities. The analysis of anonymised inventory data provides an understanding of the number and distribution of assets, along with characteristic physical properties (construction material, height, age, purpose).
Statistical comparisons are drawn in relation to published international dam inventories. Similarities and differences in the international dam populations are noted, particularly with regard to construction era and type. The NZ portfolio is unique in that dams are typically shorter in height, and a significant proportion of structures serve the hydroelectric and energy sectors.
Analysis of the new NZID confirms the need for research that is focused on the long-term performance of aging earth dams, particularly those exceeding 40 years of age. In addition to informing research needs and foci, the new NZID provides statistics on the dam population with far-reaching industry and management applications
This paper will present the use of Root Cause Analysis (RCA) as a means of evaluating the causes for failure modes and is based on work completed for an upstream tailings storage facility (TSF) raise where significant transverse and longitudinal cracking was observed.
The design of the TSF was based on the use of a starter wall with perimeter discharge from spigots spaced at about 25 m centres along the upstream crest. The TSF was raised using an upstream design and during routine inspections two years after completion of the raise, transverse cracks of up to 30 mm were noted on the crest and longitudinal cracks up to 40 mm width were noted on the downstream slope of the raised embankments. Concerns were raised over the extent and depth of the transverse cracking and the risks they pose to piping, seepage and containment.
Field investigations including test pitting and material testing were completed to evaluate the depth and extent of the cracking. The findings from field investigations, together with a review of the historical aerial photographs and superposition of the cracks and the locations of the spigots were then used in a Root Cause Analysis workshop.
Discussions on all causes for the cracking, asking the question “why did the problem occur?”, and then continuing to ask “why that happened?” until the fundamental process element that failed was reached”.
During the workshop, the most significant contributors for the transverse and longitudinal cracking and the likely location, extent and size of the cracks were evaluated. This identified the potential for traditional structural hog and sag bending moments causing the transverse crest cracking with the potential for transverse cracking at the interface of the raise and the original tailings. This was not previously identified as a potential piping location. The longitudinal cracking was considered to be mainly owing to settlement of the upstream tailings.
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.
Mohammad Okhovat, Viculp Lal, Neil Sutherland
The precast, prestressed concrete penstocks at Meridian Energy’s Benmore power station in New Zealand have attracted attention since construction about 50 years ago because of their unusual design. They are listed as the world’s first prestressed penstocks. However, their seismic capacity has been determined to be insufficient when measured against Meridian’s current asset management objectives aimed at avoiding significant damage to generating assets in a 1:2,500 year AEP earthquake. The deficiency is mainly due to the relatively narrow base width of the penstocks.
In this study, a series of linear analyses was performed to obtain an improved understanding of seismic behaviour of the penstocks. Various strengthening solutions are under consideration for the penstocks to meet the acceptance criteria. Additionally, nonlinear analysis of the penstocks was carried out to investigate the use of seismic damping devices fitted to the penstocks, similar to damping applications in seismic response control of buildings and bridges.