2008 – Design and construction of a flood mitigation dam on the North Para River, using high-paste RCC
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.
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Papers 2008
2008 – Inelastic seismic analysis of Dartmouth Intake Tower
Learn moreFrancisco Lopez, John Bosler
Abstract: A study has been undertaken to determine the structural adequacy of the Intake Tower for the Dartmouth Dam Low Level Outlet Works under the Maximum Design Earthquake (MDE). The tower is a reinforced concrete frame structure. The study included the definition of appropriate seismic inputs and nonlinear time-history analyses for different levels of ground shaking.
The behaviour of the tower was assessed in terms of material strains. The seismic acceleration-time history was applied to the model and the nonlinear analysis identified the locations in the structure which reached the following performance thresholds: cracking of core concrete, yielding of reinforcing steel, fracture of reinforcing steel and crushing of core concrete.
The results of the study showed that the tower was able to resist, without collapse, the loadings imposed by three different MDE acceleration time-histories. The predicted level of damage consisted of generalised yielding of reinforcement, formation of numerous plastic hinges at different locations in the tower and generalised spalling of cover concrete.
Overall, the structural response of the tower under the MDE events was considered satisfactory and met the performance requirement that structural collapse should not occur.
Keywords: intake tower, nonlinear, inelastic, time-history, seismic analysis.
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Papers 2008
2008 – Modelling procedures used for the spillway upgrade for Lake Manchester Dam
Learn moreEric 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.
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Papers 2008
2008 – Thermal modelling of the mass concrete in the Hinze Dam spillway raise
Learn moreScott 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
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Papers 2008
2008 – Best practices in dam safety risk analysis at the Bureau of Reclamation
Learn moreGregg A Scott
Abstract: The Bureau of Reclamation has been performing quantitative risk analysis as the primary dam safety decision making tool for well over a decade. This paper summarizes some of the key concepts and basic methodology currently used in the dam safety risk analysis process at Reclamation.
Keywords: dam safety, risk analysis, reliability analysis, event trees, subjective probability.
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Papers 2008
2008 – Geotechnical risk assessment and management for hydropower development sites in the Indian Himalaya
Learn moreRobert Goldsmith
Abstract: Selection of suitable dam and associated structure sites for run-of-river hydropower projects in the Himalayan region requires a thorough assessment of the hazards and the consequences of their occurrence. Typical projects in this environment of deep ridge and ravine terrain comprise concrete gravity dams with steel flood or sluice gates. The steep abutment slopes generally require spillways to be over the dam crest and not as separate structures.
Hazards to be considered for such structures are linked mainly to geological and hydrological factors and include landslides both at the dam and in the reservoir, outwash floods from a variety of initiating causes (landslide dams or glacial melt), floods from storm events, weak or unstable foundations, seepage and pore pressures and earthquakes. Each hazard is related to a risk scenario and a matrix of events is evaluated for potential cause, consequence and impact. A measure of consequence to the project at various stages of design, construction and operation is obtained and provides a basis for preparing risk mitigation measures. Risk management plans can then be prepared using a forum process with stakeholders to achieve a satisfactory outcome.
Examples are provided from specific studies carried out for hydropower projects in the Indian Himalaya. They include a risk assessment of a floodwave overtopping a dam from debris torrent after breaching of a landslide formed dam, terrain studies and geomorphological assessment to locate landslides in dam abutments and design and construction issues relating to a project site astride a major tectonic thrust zone.
Keywords: geotechnical risk, hazard and risk matrix, risk management plan, landslides, landslide dams, hydropower dams and tunnel, Himalayas
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