Stuart Richardson, Peter Liepkalns, Rod Mauger
Abstract: Operations and maintenance of large dams can be complex and potentially high risk. Even on a relatively new dam like Dartmouth, Goulburn-Murray Water is regularly presented with maintenance tasks which are made very difficult because access for maintenance may not have been considered during the original design and construction of the dam.
Goulburn-Murray Water recently completed a change over of a 200mm cast iron gate valve at Dartmouth, not in itself a complex or high risk maintenance task. What made this task challenging was that the valve was subject to full reservoir head (up to 180m) with no means of isolation.
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Dr AK Hughes
Abstract: This paper describes the way in which the UK is moving in respect of reservoir safety and outlines the legislative changes that are currently being drafted. It also identifies issues which the author thinks are important for the future of dam engineers around the world.
Keywords: safety, legislation, risk assessment
Jerome Argue, Steven Slarke, Douglas Rudd
Abstract: The North Para River Flood Control Dam is an integral part of the works proposed to manage flood risk in the Gawler River, north of Adelaide. Undertaken by the Gawler River Floodplain Management Authority (GRFMA), an authority representing the six local Councils in the area, the flood storage is located on the North Para River, about 10 kms north of Gawler. Roller Compacted Concrete (RCC) was selected for the construction material, based on an assessment of the geotechnical and geological site conditions, together with advantages of reduced cost, time and structure required to pass design flood events. With an overall project cost of $16.1 million, the dam was constructed on time and well within pre-tender budget estimates.
Keywords: flood mitigation, roller compacted concrete, North Para River, construction.
Scott Jones, David Hughes, Orville Werner
Abstract: As part of the 15 m raise of Hinze Dam, the existing 33 m high mass concrete spillway structure will be raised an additional 12.5 m. This will be achieved using conventional mass concrete placed on the top and downstream side of the existing spillway to form a new monolithic structure. Heat generated by the hydration of the cement and fly-ash will raise the peak temperature in the body of the new concrete relative to the stable and relatively uniform temperature within the existing concrete. The early, comparatively rapid volume expansion (and subsequent slow contraction) of the new concrete is externally restained along the interface and there is a potential for tensile stains to develop along the interface that are large enough to cause cracking through the body of the composite dam and potentially compromise the interface bond. The temperatures and thermal gradients induced are a function of the mix design, particularly the amount and thermal properties of cement used, and the sequencing of construction.
Two-dimensional transient coupled thermal-structural finite element (FEM) analyses were used to predict thermal deformations and stresses within the body of the spillway in the weeks and months after placement. Laboratory measured mechanical and thermal properties of the concrete and local boundary climatic data were input to the analyses. The measured adiabatic calorimeter curve showed that the fine grind and chemical composition of the local South East Queensland cement produced a rapid generation of heat which magnified potential thermal expansion issues with the early-age concrete.
Creep, shrinkage, viscous-elastic behaviour, and the increase in modulus of elasticity with age influence the degree to which expansion and contraction of the concrete are converted into stress. These variables, were either accounted for directly in the elastic FEM model, or were taken into account in the interpretation of the results.
This paper presents the assumptions, methods, and criteria used in the FEM analyses; the results of the material testing program; and the results and conclusions drawn from the analyses. A discussion on the concrete mix design trials recently completed on site is also included.
Keywords: Adiabatic Temperature, Creep, Mass Concrete, Placement Temperature, Pre-cool
G. Shams Ghahfarokhi, PHAJM van Gelder, JK Vrijling
Abstract: Risk and reliability analysis is presently being performed in almost all fields of engineering depending upon the specific field and its particular area. Probabilistic risk analysis (PRA), also called quantitative risk analysis (QRA) is a central feature of hydraulic engineering structural design.
Actually, probabilistic methods, which consider resistance and load parameters as random variables, are more suitable than conventional deterministic methods to determine the safety level of a hydraulic structure. In fact, hydraulic variables involved in plunge pools, such as discharge, flow depth, and velocity, are stochastic in nature, which may be represented by relevant probability distributions. Therefore, the optimal design of a plunge pool needs to be modelled by probabilistic methods.
The main topic of this paper is concerned with the reliability-based assessment of the geometry of the plunge pool downstream of a ski jump bucket. Experimental data obtained from a model of a flip bucket spillway has been used to develop a number of equations for the prediction of scour geometry downstream from a flip bucket spillway of a large dam structure. The accuracy of the developed equations was examined both through statistical and experimental procedures with satisfactory results. In addition, reliability computations have been carried out using the Monte Carlo technique.
The main conclusions are that structural reliability analysis can be used as a tool in the dam safety risk management process and that the most important factors for further analysis are erosion, friction coefficient, uplift and self-weight.
Keywords: risk analysis, reliability, plunge pool, Monte Carlo simulation, flip bucket, large dams
Eric Lesleighter, Bronson McPherson, Karen Riddette, Jon Williams
Abstract: The paper describes in part the hydraulics investigations required for the major upgrade works for Lake Manchester Dam; investigations which utilised two modelling procedures. Following a brief outline of the dam rehabilitation program and works, the inadequacy of the former spillway for the revised hydrology is described. The urgency of the construction program led to the use of CFD modelling following preliminary desk studies of the hydraulics, in order to delineate certain features of the new spillway and the plunge pool area and allow the construction program to be fast-tracked. As part of the overall program to refine the spillway design, and due to the evident complexity of the flows over the spillway, physical hydraulic model studies were also carried out.
The investigations provided a very good opportunity to compare the results from two modelling approaches carried out within the same design activity. Specific results of aspects such as flow patterns, velocities, pressures, and wave action will be compared. A prominent purpose of the paper will be to acknowledge the advantages and limitations of both approaches, and seek to provide the guidelines and advice that designers and dam owners should follow and adopt to ensure the hydraulics requirements of projects are soundly engineered.
Keywords: spillways, physical modelling, numerical modelling, CFD.