A concrete-rockfill composite dam consists of two zones: a slender concrete gravity section and a rockfill embankment section. Each zone behaves according to its stiffness and geometry during earthquake shaking. At the abrupt interface a structure behavioural discrepancy results. To mitigate such this discrepancy, a transition interface is introduced by gradually tapering the concrete section down and burying into the central part of rockfill embankment. However the behaviour of the interface is complex due to the two intermeshing of the different materials. Previously, the interface was not designed with any serious theoretical approach, but with the intuitive belief that the transition structure can play the role of mitigating behavioural difference between concrete and rockfill sections. This study seeks to characterize the dynamic behaviour of each section and to understand the performance of the interface using centrifuge model test and numerical analyses. The centrifuge model, which was reproduced by scaling down D dam in Korea, were loaded with adjusted seismic forces based upon seismic coefficient of 0.098g and 0.154g required in the dam design criteria. The legitimacy of the model test was verified by the comparison of the test results with those of numerical analyses, and the most appropriate input values for the interface elements were proposed through a systematic parametric analysis. The key findings of the paper are as follows: Numerical parameters study of the interface-element was carried out, the friction angle depends on rockfill zone material and normal and shear stiffness coefficient of the two materials (concrete and rockfill), the average values were found to be the most appropriate. The findings of this study can be used to design new composite dams, rehabilitate current dams, or design additional spillways to current rockfill dams.
Keywords: Composite dam, Centrifuge, Interface-element
The Bureau of Meteorology (the Bureau) is revising the current Intensity-Frequency-Duration (IFD) design rainfall estimates which are an essential component in the design of infrastructure. The current IFDs were developed by over 20 years ago using data from the Bureau’s network of rain gauges and adopting techniques for the statistical analysis of the data that were considered appropriate at the time.
The IFD Revision Project, which will provide revised IFD estimates in November 2012, uses a greatly expanded rainfall database in addition to adopting more statistically rigorous methods that are most appropriate to Australian rainfall data. The revised IFD estimates will be provided for durations from 1 minute to 7 days and Annual Exceedance Probabilities (AEPs) from 50% to 1%. The revised IFD information will be blended with the CRCFORGE estimates developed by each state to enable a smooth rainfall frequency curve to be derived from 50% AEP to 0.05% AEP.
Keywords: Design rainfall, Intensity-Frequency-Duration, IFD .
Mike Phillips, Kelly Maslin
A spillway upgrade conceptual design and selection process was undertaken to identify options for upgrading the Dartmouth Dam to pass the Probable Maximum Flood (PMF). A number of upgrade options were investigated, including variations of dam raise heights and spillway modifications. One of the options, the piano key weir, was initially developed from the limited available publications on the weir design, and further developed with the use of a 1:60 scale model. The piano key weir, a variation of the labyrinth weir, is a passive spillway that utilises a total weir length several times that of the effective spillway width. For the Dartmouth Dam study, the piano key weir design that was developed consisted of a 7-cycle, 9 m high structure, with a total weir length of nearly 600 m, or more than 6 times the existing effective spillway width of 91 m. The spillway was designed to pass the routed PMF outflow of approximately11,500 m3/s with a head of approximately 11 m.
The piano key weir design was developed using the following analyses:
Initial 1:60 scale physical model of the piano key weir based on published papers on piano key weirs and design manuals for labyrinth weirs;
Structural analysis and weir member sizing using initial physical model results;
Computational Fluid Dynamics (CFD) modelling to improve the hydraulic efficiency of the weir for the range of flows;
Revised 1:60 scale physical model of the piano key weir; and
Confirmation of conceptual structure design.
This paper describes the process of developing the piano key weir option for the Dartmouth Dam spillway and lessons learned.
Keywords: Piano key weir, CFD, spillway, physical model
The Enlarged Cotter Dam project was selected as a key component in securing the future water supply for Canberra and the ACT region. The RCC gravity dam, when completed, will stand 84m high and will be the largest of its kind in Australia.
The dam was designed, and is currently being constructed, under the Alliance contract model. The collaboration this model brings between the owner and the design and construction teams facilitated a drive in innovation from the design through to the construction stages of the project. The focus of this paper is on some of the key innovative aspects of the project, for consideration on future RCC and dam projects.
Investigation was made into the placement of RCC in 400mm layers, compared to the industry adopted standard of placement in 300mm thick layers. Whilst full scale trials demonstrated that placement in 400mm thick layers was not detrimental to the quality of the RCC, the benefits in terms of increased production were never fully realised due to adverse weather and the geometry of the dam placement area. Some issues were also encountered with regards to the compaction of the GERCC on the dam faces. The results do however suggest that the method warrants consideration on future RCC projects.
The construction of the dam’s secondary spillway included a waterstop installation in a constrained RCC placement zone. By developing an arrangement that could hold the waterstop in place and induce the movement joint in the correct location, this arrangement simplified what could have been a complicated procedure in an already time consuming placement area.
The start of RCC placement was at risk of further delay on account of the extensive mass concrete pours required to level the dam foundation. A conventionally vibrated concrete mix, made from the existing site won RCC materials, was designed so that it could be produced from the RCC batch plant. This method of concrete production, combined with an efficient means of delivering the concrete to the pour area, accelerated the placement process and reduced the cost of construction.
Keywords: RCC, dam, construction.
Steven Hare, Daniel Masters, Phil Farnik
State Water Corporation, New South Wales’ bulk water delivery business, is enhancing its maintenance planning and execution through a maintenance improvement project. This project incorporates a Reliability Centred Maintenance (RCM) analysis of water infrastructure assets including dams, weirs and pipelines and refining current maintenance procedures.
The project aims to address inconsistencies in maintenance frequencies and applications that have resulted from historically managing assets at a regional level. This project, coupled with State Water’s new “functional based” organisational structure, is expected to yield an effective and consistent preventive maintenance program across the organisation. The project is also expected to increase the reliability of critical dam infrastructure and aid in maintaining safe operation of the organisation’s assets.
This paper briefly describes the history of maintenance, principles of RCM, project implementation aspects and early outcomes. These outcomes include the reduction of maintenance frequencies on non safety critical assets with low failure rates, elimination of ineffective tasks and standardisation of maintenance frequencies on equipment common to all dam sites.
Keywords: Reliability centred maintenance, dams, weirs
David Hilyard, William Ziegler, Heather Middleton
New South Wales has a significant number of dams, including major water supply dams, located over or near mines. Mining near dams imposes dam safety risks including: mine subsidence, mine blast vibration, presence of mine personnel downstream, rapid changes in consequence during mining, and loss of stored waters. The NSW Dams Safety Committee(DSC) regulates mining near dams, using risk assessment to review applications to mine near dams. A structured approach allows rational, evidence-based decision making by stepping through a procedure involving: initial consultations, screening risk assessment, evaluation of technical arguments, risk assessment, and development of risk management strategies. The risk assessment for dam walls develops acceptance criteria, reviews 19 possible risks to dam walls, and site-specific hazards. For potential for loss of stored waters, four possible groups of flow paths from storage to underground mine are reviewed; flows are evaluated with Monte Carlo simulation in terms of tolerable loss. Risks are assessed from a dam engineering viewpoint, which may be more conservative than the perception of risk in the mining industry, considering both tolerable risks and operational time frames. Case studies include: a tailings dam 100 m upstream of an active open cut and underground portal was undermined by longwall mining, with about 1.5 m subsidence of parts of the embankment as each of four longwall panels was extracted; longwall mining beneath a major Sydney water reservoir, with no observed impact on the stored waters; and open cut mining immediately downstream of a mine water dam. Risk-based methodology has provided the DSC with increased confidence in reviewing applications to mine near dams.
Keywords: Mining, dams, risk assessment, New South Wales, Dam Safety Committee