Ken Ho, Robert Davey and Jim Walker
The Aviemore Dam appurtenant structures were upgraded for seismic performance in 2006. A comprehensive dam safety review programme conducted by Meridian Energy evaluated the performance of the dam and appurtenant works under extreme ground movements and rupture displacements of the Waitangi Fault, which passes through the embankment dam foundation. The spillway and sluice gates are key elements of the dam safety critical plant for the passage of floods to prevent overtopping or emergency dewatering of the reservoir after a major seismic event if there are concerns about damage to the dam. This paper outlines the assessment undertaken for the spillway and sluice gates for seismic performance and the upgrade necessary to safeguard their integrity for operation after the event.
The spillway and sluice gates are large steel radial gates operated by electrically powered wire rope winches and hydraulic actuation, respectively. Combined hydrostatic and the Safety Evaluation Earthquake (SEE) induced hydrodynamic loads would be expected to stress the gate structures beyond their yield capacity. The yield would be downstream only due to the influence of the hydrostatic load under the earthquake response cycle. The resulting deformations were predicted to fracture connecting bolts in the spillway gate arms and cause severe leakages past the top leaf of the sluice gates. The solutions developed for the spillway gates to reduce connection bolt damage and the strengthening of the sluice gates will ensure their post-earthquake operation.
Keywords: Aviemore Dam, spillway, sluice, radial gate, seismic performance, post-earthquake operation.
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Mike 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
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
M.G. Webby, C.J. Roberts and J. Walker
The Waitangi Fault passes under Aviemore Dam and Lake Aviemore in the Waitaki Valley in the South Island of New Zealand. Several studies were undertaken in the period 1999-2004 to understand the geology and faulting in the Waitaki Valley and, in particular, to determine the potential for future movement on the Waitangi Fault (Walker et al. 2004). As part of the Aviemore Dam Seismic Safety Evaluation (ADSSE) Project, a numerical hydrodynamic study was undertaken to analyse the pattern of seiche waves generated by fault displacement and to determine the potential wave run-up on the dam face to overtop the dam.
Ground displacement along the Waitangi Fault gives rise to initial wave trains on the lake surface travelling in opposite orthogonal directions away from the fault line and approximately parallel to the axis of Aviemore Dam. These initial wave trains are refracted by the lakebed as they approach the eastern and western lake shorelines and are then reflected off these shorelines. The reflected wave trains interact to create a very disturbed lake surface before a long-period seiching response is set up due to repeated lakeshore reflection. The seiching response is a bimodal one, with a cross-lake component and an along-lake component. The along-lake seiche waves run up on the relatively steep embankment part of the dam and on the vertical face of the concrete gravity part.
Keywords: Seismotectonic, fault, displacement, lake, dam, numerical, hydrodynamic, model, seiche, wave, solitary wave, wave run-up, dam overtopping.
Stephen McInerney, Donald A. Bruce and John Black
An historical database of North American dam anchoring experience has been recently assembled in the United States. This database clearly shows the historical development of dam anchoring technology, particularly with regard to corrosion protection practices over four decades. The results of this research are significant to dam owners worldwide because of the number of examples in the database.
The paper describes New Zealand experience with dam anchoring against the background of the historical practices in North America and the main conclusions drawn from the United States research.
Keywords: Post-tensioning, anchor, corrosion protection, historic database, dam remediation
Bruce Walpole and Craig Scott
Monitoring and surveillance is crucial to managing the ongoing performance of dam structures.
The true value of appropriate monitoring, surveillance and review processes is only realised when
potential dam safety issues arise. TrustPower’s civil safety monitoring and surveillance program
includes nineteen hydro schemes throughout New Zealand and incorporates structures with
Potential Impact Classifications (PIC) ranging from Low to High.
TrustPower promotes a continual improvement policy on its management of safety issues and
conducts inspections on a regular basis. Routine and periodic independent inspections of the key
components within a scheme are paramount to the viability of the safety management system. The
importance and purpose of these inspections has recently been highlighted by the discovery of two
sinkholes on the face of the earth dam associated with the Cobb hydro electric power scheme.
This paper provides an example of the need for continual monitoring and surveillance, vigilance
of observations, good archiving systems and documentation. It discusses the broader issues
surrounding the subsequent response processes to potential dam safety deficiencies, and the
success (or otherwise) of investigative methods. It also highlights that an adequate dam safety
compliance system has commercial value as there is a measurable reduction in dam performance
uncertainty and hence greater efficiency in the speed at which accurate resolutions can be drawn.
Keywords: Dam safety, embankment, sinkholes, foundations, dam drainage, geophysical