2007 – Current international state of practice for the seismic design and analysis of appurtenant structures at dams
Steve O’Brien
Appurtenant structures associated with a dam play and important part to the dam’s operation. For these structures it may be important that their functional and structural integrity is retained in the event of a notable earthquake, particularly when they are required to release water from the reservoir in a controlled manner to lower the storage following an earthquake. Research has been conducted into the current state of practice for the seismic design and analysis of these structures, including review of the main issues for seismic effects, documentation of case histories and review of current research, international guidelines and standards. The general assessment philosophy was found to be relatively consistent internationally, however, the adopted assessment procedures were found to vary. The status of the current ANCOLD earthquake guidelines has been provided in relation to the current international state of practice for various types of appurtenant structures.
Keywords: Appurtenant structures, performance criteria, seismic performance, seismic analysis.
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2007 Papers
2007 – Design inputs for stability assessment of dams on New Zealand greywackes
Learn moreStuart 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 – The geotectonics and geotechnics of the Traveston Crossing Dam foundation
Learn moreMike Marley, Greg Dryden, Geoff Eades, Edwin Brown, and Gary Huftile
Traveston Crossing Dam is proposed for construction at AMTD 207.6 km on the Mary River, about 25 km upstream of Gympie in South East Queensland. The Mary Valley at the dam site is located in a zone of complex geology resulting from formation in a tectonic accretionary wedge setting. This has been responsible for its complex geological structure, which has required a range of geological and geotechnical investigation and interpretation techniques to develop a model on which to base the dam’s preliminary design. This paper describes the tectonic history and the innovative techniques used in developing the geological model for the dam foundation.
The investigation involved aerial photograph interpretation, geological mapping; geotechnical drilling, including water pressure testing; seismic refraction profiling; downhole geophysical logging; excavation and geological mapping of large excavations; and hydrogeological investigation involving investigative drilling and pumping tests.
A Vulcan 3-D computerised geological model was constructed using borehole data, seismic refraction interpretation and downhole geophysics interpretation. The geological model has been used in the development of the preliminary design and confirms that the foundations are suitable for the proposed structure.
Keywords: Dam Foundation; Geophysics; Investigation Tectonics; Geological Strength Index Kinetic Analysis
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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 – Seismic hazard assessment of the Lake Edgar Fault
Learn moreA. Swindon, M. Gillon, D. Clark, P Somerville, R. Van Dissen and D. Rhoades
The 45 km long Lake Edgar Fault in south-west Tasmania passes through the right abutment of the Edgar Dam and into Lake Pedder, and within 30 km of three other large dams. In 2004 an independent seismotectonic study concluded that the fault had moved three times in the past 48–61,000 years, with the last movement around 18,000 years ago.
In order to better constrain the risk assessment for the nearby dams, the likelihood of a rupture recurrence along the fault was required. Two independent methods were investigated. The first was a comprehensive review of active faulting and deformation of stable continental region faults within Australia, and a comparison with similar faults worldwide with the well studied behaviour of the Lake Edgar Fault. The study results demonstrated the episodic nature of stable continental region fault activity, separated by much longer periods of quiescence, with a decreasing likelihood of rupture following each event within an active period. The time window of applicability of this paleoseismological study is thousands to tens of thousands of years.
The second study looked for evidence of precursory seismic activity in the vicinity of the fault which could indicate an increasing risk of rupture over the next decade or so. This method does not predict specific earthquakes, but does forecast whether the level of future earthquake activity in the short to intermediate term is relatively low, high or at an average level. Using a catalogue of seismic activity for south-eastern Australia, the study concluded that there is no evidence for precursory seismic activity in the area of the Lake Edgar Fault that would give rise to an elevated forecast rate of occurrence of moderate magnitude earthquakes either in the short to intermediate term. This precursory method has a window of applicability of a decade to perhaps several decades.
The combination of these two studies has advanced the understanding of the Lake Edgar Fault activity by both setting it in the long-term stable continental region fault context and investigating the presence of short-term behavioural activity. This has allowed the seismic hazard to be re-assessed as nearer to ambient levels than earlier postulated. This work has applicability for other fault scarps in Australia, both with regards to better defining the long-term hazard (103-105 years) posed by a fault, and potentially also giving advance (short-term 101 years) notification of increasing risk of fault rupture. Better long- and short-term hazard information allows more complete and thorough engineering decisions to be made.
Keywords: Earthquake, seismic, fault rupture, dam safety, risk assessment, Hydro Tasmania, Lake Edgar Fault.
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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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