2007 – Design inputs for stability assessment of dams on New Zealand greywackes
Stuart Read and Laurie Richards
Many dams in New Zealand are founded on greywacke, a typically hard, closely-jointed rock mass. This paper describes the characteristics of greywacke rocks based on field mapping, laboratory testing and rock mass classification, and gives examples of design inputs for dams, in particular concrete structures. Unweathered, intact rock materials have unconfined compressive strengths generally above 100 MPa and moderate to high modulus ratios. The rock masses, which comprise sandstones and mudstones, are commonly tectonically disturbed and have an unusual combination of very high intact strength and joints with low persistence. The effect of these properties on rock mass deformability and strength is illustrated by estimation of dam foundation deformability from tiltmeter measurements and assessment of critical foundation failure mechanisms from estimates of defect and global rock mass strengths.
Keywords: foundations, dam design, rock mass strength, rock mass deformability, greywacke
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2007 Papers
2007 – Planning to secure South East Queensland’s future water infrastructure
Learn moreRussell Paton and David Murray
The South-East Queensland Regional Water Supply Strategy is securing future water supplies, which includes a regional water grid and new water storages. The Queensland Government’s contribution to future water supplies includes Traveston Crossing Dam on the Mary River, Wyaralong Dam on the Teviot Brook, and Bromelton Offstream Storage and Cedar Grove Weir on the Logan River.
Queensland Water Infrastructure (QWI) was established by the Queensland Government in June 2006 to progress feasibility studies, design and construction of this new water infrastructure. QWI commissioned SunWater to investigate much of this infrastructure to preliminary design level for the impact assessment process and as supporting information for potential alliance partners for the delivery of the projects. The work undertaken included extensive geotechnical investigations, hydraulic modelling, hydrologic modelling and design activities. This paper outlines the investigations associated with the preliminary design of this infrastructure and process of risk and opportunity identification to establish the program and budgets for these projects.
Stage 1 of Traveston Crossing Dam is to be constructed by the end of 2011, with a storage capacity of 153,000 ML providing a yield of 70,000 ML each year. The design adopted for the dam consists of a roller compacted concrete structure across the valley floor with an earth embankment section on the left abutment. In order to limit inundation upstream and mitigate flooding in Gympie, a gated spillway on the right abutment has been adopted. The Traveston Crossing Dam has an estimated project cost of $1,700 million.
The design developed for the Wyaralong damsite provides a reservoir with storage capacity of 103,000 ML and a yield of 21,000 ML each year when operated in conjunction with Cedar Grove Weir. Preliminary designs have been prepared for three types of dam, which are all considered technically feasible for the site. They are a roller compacted concrete dam, an earth and rockfill dam and a concrete faced rockfill dam. The Wyaralong Dam has an estimated project cost of $500 million.
The Bromelton Offstream Storage, of earthfill construction, provides a storage capacity of 8,000 ML and Cedar Grove Weir, a sheet pile structure, provides a storage capacity of 1,000 ML and both are to be constructed by the end of 2007.
Keywords: Planning, Traveston Crossing Dam, Wyaralong Dam, Bromelton Offstream Storage, Cedar Grove Weir, Queensland, risk.
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2007 Papers
2007 – Safety assessment of mining subsidence impact on Upper Cordeaux Number 2 Dam
Learn moreDavid Ho, Chee Wei Tan and Glen Dominish
Upper Cordeaux Number 2 Dam is founded on an igneous intrusion rock mass which overlays sedimentary rock layers above the Wongawilli Coal seam. The coal mining company, BHP Billiton Illawarra Coal, planned to extract coal close to the dam. Although the dam is classified as a low hazard dam, its importance, both as part of the Sydney Catchment Authority’s water supply system and for its significant heritage value, mean that the proposed mining should not have undesirable impact on the structure. This paper describes how the mining impact on the dam was assessed using a nonlinear 3D finite element model. The model considered the pre-existing cracks in the dam wall, uplift water pressure along the dam/foundation interface and the hydrostatic pressure at full supply level. Mining-induced movement such as valley opening, closure and upsidence were applied to the model. Stability and strength assessments were made against a set of acceptance criteria developed for mining impact. The development of different stabilising mechanisms was examined. From the numerical investigation, WorleyParsons was able to provide technical advice to the mining company, the dam owner and the NSW Dam Safety Committee to facilitate the mining application and to satisfy dam safety requirements.
Keywords: Mining subsidence, Arch/gravity dam, Nonlinear numerical analysis, Safety assessment
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2007 Papers
2007 – Safety evaluation of a slab and buttress dam
Learn moreMarius Jonker, Francisco Lopez and John Bosler
This paper describes the safety evaluation and development of remediation options for Clover Dam, a 28 m high slab and buttress structure situated in the alpine region in northeast Victoria, Australia. The review was particularly challenging considering the complexity, age and cracked condition of the dam structure, which required the development of an analysis method for this type of dam.
Completed in 1953, Clover Dam is one of five dams in the Kiewa hydroelectric scheme. The 76 m long dam comprises a 45.7 m long covered slab and buttress section, supported on each abutment by concrete gravity sections. The review was undertaken as a result of severe cracking occurring since the early 1970s and because a detailed design review had not been undertaken since its construction.
Current guidelines for the safety review of existing dams provide little detailed information on slab and buttress dams. Consequently, a methodology was developed to analyse Clover Dam. This methodology could also be applied in the review of this type of dam in general, and is currently being used for safety assessments of three other slab and buttress dams.
This paper focuses mainly on the dam structural assessments undertaken during the safety review. The structural analyses involved 3-D finite element analyses for thermal, static and earthquake loading.
The outcome of the review was that both the gravity and buttress portions of the dam do not meet current design standards. The development of practicable remediation options was complicated by the operational constraints and the restricted access to those areas within the dam where remedial works were required.
Keywords: Slab and buttress dam, 3D finite element analysis, seismic assessment.
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2007 Papers
2007 – Calculating spillway crest pressures for high-head operation
Learn morePaul Hurst, Tom Ewing, Steven Fox and Bob Wark
For an ogee-shaped spillway crest, it is well recognised that sub-atmospheric pressures will develop on the lower-nappe profile for operating heads greater than design head. This effect is useful in providing an increase in efficiency of the spillway discharge for small increases in operating head. However, there is limited data on the formation of sub-atmospheric crest pressures for high-head operation above 1.3 times greater than the design head
This paper reports on modelling work done by GHD and the Water Corporation for the Wellington Dam Remedial Works Project in Western Australia where the current design flood has increased to more than twice the original design head. Two-dimensional physical scale modelling and 3-D Computational Fluid Dynamics (CFD) modelling of the existing Wellington Dam spillway profile was carried out to determine the discharge coefficient and uplift force generated by the formation of sub-atmospheric crest pressures under high-head operation.
The paper compares the results of the physical scale model and the CFD model and earlier published data by Cassidy (1970) and concludes that there exists a good correlation between the three data sets.
Keywords: Ogee, sub-atmospheric, crest pressures, Wellington Dam
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2007 Papers
2007 – Improving safety and hydraulic efficiency of dams with physical model studies
Learn moreSteven L. Barfuss and Blake P. Tullis
An important aspect of improving the safety of dams is selecting designs that are both hydraulically efficient and cost-effective. A powerful tool that can be used as part of the hydraulic structure design process is a physical model study. To obtain maximum benefit from the model, it should be implemented as a part of the design process rather than as a post-design verification phase. A model study included early in the conceptual design phase can also provide increased flexibility to the designers.
Hydraulic model studies can often provide cost-effective answers to difficult problems. Some of the issues that can be efficiently resolved using model studies include optimizing spillway head-discharge relationships to increase reservoir storage while minimizing upstream flooding potential, controlling downstream scour, quantifying hydraulic uplift forces and/or overturning moments of dam structures, evaluating alternatives for structure retrofit or repair, and optimizing control gate sequencing during floods. Model studies also allow the engineer to simulate prototype performance (e.g., three-dimensional flow patterns, velocities, pressures, scour potential) over the full range of expected discharges. Quick and easy changes to the model can be made at minimal cost when evaluating the performance, safety and economic impact of various design alternatives.This hands-on model study approach to dam safety represents a tool that in some cases is underutilized.
Brief discussions of several physical model studies conducted at the Utah Water Research Laboratory, Utah State University in Logan, Utah, USA, are presented to illustrate key points of the paper. The primary objective of each of these model studies was to provide and/or improve the safety of the dam and the spillway while minimizing construction costs. This paper discusses the cost-effectiveness and hydraulic improvements that can be achieved through physical model studies.
Keywords: Physical models studies, design, hydraulic efficiency, dam safety, construction costs
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