Shao Kwan Ng
Asset management aims to ensure that assets, such as dams, are sustainable. In order to achieve this, management decisions need to be defensible and the long-term impacts of short-term decisions need to be clearly demonstrated, such that an asset operates and is maintained in an appropriate fashion and in a satisfactory condition. Expert rule systems are becoming widely recognised as powerful and elegant tools suitable for engineering and management decision-making. They are powerful, transparent and flexible tools that mimic how people make decisions, and hence provide a natural way of thinking for decision-making. This paper reviews the current usage of expert systems in asset management, and illustrates the potential of these tools, in conjunction with the available (ANCOLD) guidelines, to assist dam owners in decision-making, such as in condition evaluation and dam hazard assessment applications.
Keywords: Decision-making, expert rule systems.
Now showing 1-12 of 41 2974:
Rick Friedel, Len Murray, Gerrad Suter, James Penman, James Watt, Hendra Jitno
The Hidden Valley tailings storage facility (TSF) has set a new precedent in environmental management of tailings in Papua New Guinea (PNG). Modern mining in PNG arguably began with the development of Bougainville Copper in the late 1960s, and continued through to Ok Tedi, Porgera, Lihir, Misima (and others). These mines have proceeded with deep sea or riverine tailings deposition, rather than construction of a tailings dam to retain the mine waste within an impoundment; as is the practice throughout the majority of the mining industry.
The Hidden Valley TSF is comprised of two large earth and rock fill dams, raised by the downstream method. Starter dam construction was completed in 2009. At final height the Main Dam will be one of the highest tailings dams in the world. The dams are constructed of pit waste and therefore have the dual function of storing tailings and waste rock.
Construction of the starter dams and subsequent raises is complicated by conditions at the site. Water management was, and remains, the dominant issue. High rainfall, weak erosive soils, material availability, dense vegetation and remoteness of the site provide constant challenges to construction. The Observational Approach to construction was recommended by the designers and adopted by the mine operator. This involves a knowledgeable pre-assessment of what is likely to change and having contingency plans to deal with possible major issues. This approach allows changes to the design during construction so the “as-built” product is suited for the site, fit for purpose, and remains consistent with the overall intent of the design.
The TSF has been in operation since August 2009 and monitoring data of the structures has been collected during construction and operation. This data is reviewed to confirm design assumptions and assess dam performance.
Personnel involved with this project combined their experiences working in the PNG environment and dam building from other locations. This process led to close interaction between the mine operators, designers and construction teams. Team work and diligent construction practices were and will continue to be necessary to construct and operate the pioneering TSF in PNG.
Hamish Smith, Graeme Maher
In order to achieve environmental sustainability it has become standard engineering practice to include a fishway on all new or refurbished large dams in Australia.
As regulators expand their understanding of fishways, project approval conditions associated with these complex engineering structures are changing. Regulators now increasingly wish to participate in the development and selection of the final fishway to be adopted.
This paper describes the process developed and implemented at Queensland’s most recent dam under construction, the Wyaralong Dam, to ensure that the views and opinions of regulators and stakeholders were sought and considered during the fishway selection and design process.
With no written guidelines available on “how to select and design a suitable fishway”, all associated parties entered into the process without a full knowledge of how it would unfold and what the final outcome would be.
This paper demonstrates that in an increasingly regulated environment it is possible to have regulators, proponents and stakeholders work cooperatively together to achieve a result that provides for sustainable development and is acceptable to all parties.
This paper will provide a model that could be adopted for the development of new fishways or the refurbishment of existing fishways on large dams in Australasia.
Changing Regulatory Environment – Large Dams and Fishways
Jiri Herza, Nihal Vitharana, Alex Gower
The Western Australia Water Corporation plans to increase the storage capacity of Millstream Dam, which is located near Bridgetown in the south west region of WA. The existing dam is an 18 m high zoned earthfill embankment constructed in 1962. The dam suffered a block heave of the foundation at the downstream toe during the first filling, probably attributable to high foundation pore water pressures. The dam upgrade will be challenging due to complex and unfavourable foundation soils coupled with these artesian pressures.
The dam is founded on lateritic soil, which is a common weathering profile throughout the region. These soils formed in a tropical environment of fluctuating water tables, severe leaching and translocation of iron oxides over many millions of years. As a consequence some of the lateritic horizons at Millstream Dam have been modified such that they exhibit behaviours that are not consistent with conventional constitutive models and correlations. These are attributed to a complex structure of the soil microfabric, which comprises clay particles bonded together into larger aggregates. The clayey aggregates are also bonded to each other, forming a porous matrix of silty or sandy appearance characterized by low dry density and high void ratio, which may nevertheless disintegrate on working.
Comprehensive geotechnical investigations and extensive laboratory testing have revealed that the foundation materials display characteristics of clayey and granular soils. Under shearing, these soils demonstrate high initial strength, which gradually reduces as the inter-aggregate bonds are broken and the relative position of the aggregates changes. Several soil samples also exhibited significant contractive behaviour on shearing generating high pore pressures under undrained conditions.
This paper presents the investigation and design methods used in the foundation design of the Millstream Dam upgrade with emphasis on unusual behaviour of the foundation media.
Challenges in dam design on lateritic soils
Keirnan Fowler, Peter Hill, Phillip Jordan, Rory Nathan, Kristen Sih
Although there are considerable uncertainties in the science of climate change, there is a growing recognition of the importance of the issue. Incorporation of climate change impacts is now required in policy guidance from several government authorities and it is prudent risk management to consider the effects of climate change in planning for water resource infrastructure, including assessment and design of dam upgrades. This paper describes the potential impact of climate change on extreme flood estimates and provides a case study for Dartmouth Dam in south-eastern Australia. Three inputs to flood estimation were considered according to the projected impact of climate change; namely design rainfalls, modelled losses and initial reservoir level. The relative influence of each of these factors is explored. Rainfall and losses had a similar (and opposite) influence on results and for this dam the reservoir level prior to the flood event had the largest influence on results. This case study demonstrates that the insights of climate modellers and hydrologists need to be integrated in order to provide defensible estimates of the impact of climate change in flood hydrology studies. Credible projections of changes in design rainfall intensities are required for the full range of exceedance probabilities across Australia.
Application of Available Climate Science to Assess the Impact of Climate Change on Spillway Adequacy
Peter A Ballantine, Christopher V Seddon
Massingir Dam, constructed in the late 1970’s on the Olifants River in Mozambique, is a 48 m high zoned earthfill dam. Due to various safety concerns, the dam was operated at a reduced full supply level of 110 masl, compared to the design full supply level of 125 masl. Between 2004 and 2006 remedial works were undertaken, including the construction of a berm on the downstream face of the dam, grouting and drainage of the foundations and installation of the spillway crest gates. From December 2005 the storage level of the dam was allowed to increase.
On 22 May 2008, with the reservoir storage level at 122.43 masl and the gates on the outlet conduits closed, the reinforced concrete conduits failed at the downstream end, releasing an estimated 1,000 m3 /s of water into the Olifants River.
A 2-D finite element analysis was undertaken in order to establish the safe load bearing capacity of the as-constructed conduits. On the basis of the analysis, it was concluded that the original design did not take proper account of the pressure that would develop within the thick concrete sections of the conduit. In view of assumptions regarding the load paths, the reinforcement was not placed in the most appropriate positions.
This paper describes the events leading up to the failure of the conduit, presents the findings of the investigation into the failure and makes recommendations on the basis of the findings.